Clinical Neurologic Evaluation

The neurologic sciences are the most intellectually challenging, unequivocally fascinating, and tremendously stimulating of the various clinical disciplines. Initially, the vast intricacies of basic neuroanatomy and neurophysiology often seem overwhelming to both medical student and neuroscience resident alike. However, eventually the various portions of this immense knowledge base come together in a discernible pattern, not unlike a Seurat canvas. Often one is expanding or revisiting our neurologic base as we are challenged by variations on the theme of our previous experiences. It is the keen observation and coding of these clinical experiences that lead the astute neurologic physician to solve new patient challenges.

One must first and foremost be an astute historian initially listening very carefully to the patient. Most often the intricacies, as well as the subtleties, of the neurologic history provide the essential foundation leading to a rational and structured neurologic examination allowing the neurologist to answer two basic questions: WHERE is the lesion and WHAT is the likely etiology. This will guide the clinician in ordering the appropriate diagnostic testing.

Although it is easy to define the requisite methodology to examine the neurologic patient, it is much more challenging to similarly address the history acquisition other than making a few generalities. One of the most important elements of neurologic training is the opportunity for the student and the resident to observe senior neurologists evaluate a patient. As a resident, this was absolutely one of our most important learning experiences. Too often the student does not appreciate the elegance illustrated by a carefully derived neurologic clinical history. A major attribute of a skillful and successful neurologist is being an astute listener. This requires the neurologist to bring together various seemingly disparate and subtle data from the patient's various concerns and then focus on this information with specific questions to decide on its relevance to the issues at hand. Understanding the temporal profile of the patient's symptoms is crucial; was the symptoms’ onset acute and stable, or has it followed an ingravescent course? Very often, this information provides a most important perspective that is one of the very important keys to diagnosis.

Clinical Vignette

A 42-year-old woman with juvenile autoimmune diabetes mellitus came for further investigation of her extremely painful neuropathy initially presumed secondary to diabetes, or possibly to recent chemotherapy for breast cancer. However, her temporal profile was the final clue to her diagnosis. On careful review of the onset of her symptoms, it was found that she had never had the slightest hint of intolerable paresthesia until awakening from her mastectomy. Her pain had begun precipitously in the recovery room. It was steady from its inception and totally incapacitating in this previously vigorous woman whose favorite pastime was backpacking in mountainous national forests. This temporal profile was in total contradistinction to any symmetric diabetic or antineoplastic chemotherapy-related polyneuropathy. These disorders always have a clinical course of subtle onset and gradual evolution.

With this information, we investigated what transpired at the time of her breast surgery when she awakened with this extremely limiting painful neuropathy. In fact, she had had a general anesthetic with nitrous oxide (N ₂ O) induction. This N ₂ O uncovered a second autoimmune disorder, namely vitamin B ₁₂ deficiency. The anesthetic had precipitously led to symptoms in this previously clinically silent process. Fortunately, vitamin B ₁₂ replacement led to total resolution of her symptoms.

Comment: In this instance, her initial physicians had let themselves be trapped by what was familiar to them because diabetes is the most common cause for a painful neuropathy. However, only rarely does it lead to a precipitous onset of symptoms. The fine-tuning of this patient's temporal profile, especially the abrupt onset of symptoms, led us to seek a more detailed history as to whether some toxic process was operative. Review of the operative records per se led to the diagnosis when the suspicion of N ₂ O intoxication was confirmed.

Most neurologic disorders follow a well-defined clinical paradigm. However, it is their very broad clinical perspective that continually challenges the astute neurologic clinician to maintain a vigilant intellectual posture. When these specific clinical subtleties are appreciated, the clinician is rewarded with the knowledge of having done the very best for his or her patient, as well as having the intellectual reward for being on the cutting edge of the clinical neurosciences. The skillful clinician, taking a very careful history, is the one most able to recognize the attributes of something quite uncommon presenting in a fashion more easily confused with more mundane afflictions.

For example, numbness or tingling in a patient's hand most commonly represents entrapment of the median nerve at the wrist, reflecting the presence of a very common disorder known as the carpal tunnel syndrome. However, symptoms of this type may occasionally represent early signs of a pathologic lesion at the level of the brachial plexus, nerve root, spinal cord, or brain per se. It is imperative for the clinician to always consider a broad anatomic perspective in each patient evaluation. When this approach is not carefully followed, less common and potentially treatable disorders may not be diagnosed in a timely fashion. It is absolutely imperative that no compromise be made in obtaining a thorough and accurate history when first meeting the patient. This is the most important interchange the physician will have. It needs to be taken in a relaxed, hopefully uninterrupted setting allowing for privacy. In addition, it is very important to invite the spouse, parent, or significant other into the room. Rarely will a patient object to this; having another close observer of a patient's difficulties available can provide insights that may be essential to diagnosis. A thorough initial evaluation engenders a patient-family sense of trust in the physician as a detailed history, with a careful examination demonstrates a major commitment. Once developed, this clinical setting encourages patients to communicate openly with their physician as they outline their diagnostic plans and eventually a treatment formulation. This chapter provides a foundation that will serve as an anchor for both the student and resident as they learn the art and science of the performance of detailed neurologic evaluations.

Neurologic History and Examination

An accurate history requires paying attention to detail, often observing the patient's demeanor while reading the patient's body language, having the opportunity to witness the patient's difficulties, and interviewing family members. History taking is a special art and science in its own right. It is a skill that requires ongoing additions to one's own interviewing techniques. Listening to the patient is a most important part of this exercise; it is something that can be more time consuming than current clinical practice “time allowed guidelines” provide for within various patient settings. This approach provides the diagnostic keystone that often distinguishes an astute clinician's ability to find a diagnosis where others have failed.

A complete neurologic examination also requires carefully honed clinical skills. For example, the ability to decide whether the patient is truly weak and not giving way, or similarly does or does not have a Babinski sign present, is key to arriving at a correct diagnosis. The ability to define a sensory loss at a spinal cord level is another very crucial exercise.

One challenging clinical scenario occurs with patients who have seen other clinical neurologists and no diagnosis was made. The patient is frustrated, as often is the prior neurologist. To be fair to the patient, as well as oneself, when evaluating such an individual seeking a second neurologic opinion, it is important to gain one's own initial and totally unbiased history and examination. Furthermore, to prevent unwelcome bias, the new neurologist should avoid reading other colleagues’ notes or looking at previous neurologic images prior to gaining his or her own history and performing the examinations.

Although time consuming, the history is the most important factor leading to accurate diagnoses. One of the essential attributes of a skillful neurologist is the ability to be a good listener so as not to miss crucial historic points. It is important to begin the initial meeting by asking patients why they have come; this offers them the opportunity to express concerns in their own words. If at all possible, the neurologist should not interrupt, thus providing the patient the opportunity to provide their primary concerns to the neurologist, emphasizing the symptoms of greatest importance. Rarely, anxious or compulsive patients may speak of their concerns at great length; with experience, physicians learn to make discreet interjections to maintain control of the evaluation and draw the patient back from extraneous tangents.

When the patient's primary concerns are established, specific issues can be explored. In addition, making careful observations during the review of history allows better focus for subsequent questions. An accurate baseline assessment of mental status and language can be obtained from listening to the patient and observing responses to questions. It is through listening that the clinician gains insight into the patient's real concerns. For example, it is not unusual to see a patient referred to a neurologist for evaluation of headaches, which only became exacerbated with the recent discovery of a brain tumor in someone known to the patient.

Unfortunately, the economics of modern health care has forced primary care physicians and specialists to shorten visit times with patients and their families. One must be fastidious not to use diagnostic tools, such as magnetic resonance imaging (MRI), as substitutes for careful clinical history and examination. The current detailed medical information available on the internet, in conjunction with sophisticated basic health education, has indeed enhanced patients’ knowledge, although not always in a balanced format. Patient expectations may affect the diagnostic approach of physicians. In this environment, it is not surprising that imaging techniques such as MRI and computed tomography (CT) have replaced or supplemented a significant portion of clinical judgment. However, even the most dramatic test findings may prove irrelevant without appropriate clinical correlation. To have patients unnecessarily undergo surgery because of MRI findings that have no relation to their complaints may lead to a tragic outcome. Therein lies the importance of gaining a complete understanding of the clinical issues.

Although neurology may seem in danger of being subsumed by overreliance on highly sophisticated diagnostic studies, this needs to be kept in perspective because many of these innovations have greatly improved our diagnostic skills and therapeutic capacities. For example, much knowledge regarding the early recognition, progression, and response to treatment of multiple sclerosis (MS) depends on careful MRI imaging.

It is essential to make patients feel comfortable in the office, particularly by fostering a positive interpersonal relationship. Taking time to gather information about patients’ lives, education, and social habits often provides useful clues. A careful set of questions providing a general review of systems may lead to the key diagnostic clue that focuses the evaluation. When the patient develops a sense of confidence and rapport with an empathetic physician, he or she is more willing to return for follow-up, even if a diagnosis is not made at the initial evaluation. Sometimes a careful second or third examination reveals a crucial historic or examination difference that leads to a specific diagnosis. Follow-up visits also allow the patient and physician to have another conversation regarding the symptoms and concerns. Some patients may come to their first office visit with an exhaustive list of concerns and symptoms, whereas others provide minimal information. Subsequent visits are intended not only to discuss the results of tests but also to clarify the symptoms and/or response to treatment. If patients feel rushed on their first visit, they may not return for follow-up, thus denying the neurologist a chance at crucial diagnostic observations. The physician-patient relationship must always be carefully nurtured and highly respected.

Approach to the Neurologic Evaluation

Throughout training, examination skills are continually being amplified as the resident is exposed to an ever-evolving clinical experience. One important learning opportunity is the observation of the varied skill sets demonstrated by academic neurologists as they approach different types of patients. One of the essentials of the neurologic evaluation is learning how to elicit important, sometimes subtle, clues to diagnosis; in addition, an appreciation of what is “normal” at different ages is also important. A hasty history and examination can be misleading. For example, briskly preserved ankle reflexes in an elderly patient is not normal, whereas moderately diminished vibration sense at the ankles is normal. A diagnosis of early MS may be missed by not asking about such things as previous problems with visual function, shooting electric paresthesia when bending the neck (Lhermitte sign), or sphincter problems manifested by increasing urgency to urinate.

Even though carpal tunnel syndrome is the most common cause of a numb hand, one must always be fastidious not to overlook other pathoanatomic sites that could result in the same symptoms, such as the more proximal median nerve, brachial plexus, or cervical nerve root. In another instance, the failure to perform a thorough neuromuscular examination (including asking the patient to change into a gown and inspecting muscle bulk and tone) may preclude the examining physician from recognizing the presence of an unexpected subtle spasticity, reflex asymmetry, and/or a Babinski response indicative of a central nervous system (CNS) lesion. Similarly, identifying a sensory level is indicative of a myelopathy as the pathophysiologic explanation for the patient's numb hand. Lastly the finding that the sensory loss in the fingers primarily involves position sense and stereognosis becomes the entrée to examine the cerebral cortex as the site for these complaints.

Another important outcome from performing a complete neurologic examination at the initial evaluation in almost every patient is that this not only establishes the patient's current status but will also provide a baseline for future comparison. There are certain “normal” asymmetries in many individuals, often not previously appreciated by the patient or relatives. These may include a patient's slightly asymmetric smile, somewhat irregular pupils, or hint of ptosis. However, at times such findings do take on significant meaning. As an example, a middle-aged woman was thought to have benign tension headaches. This was based on a “normal” neurologic exam elsewhere. However, she had an asymmetric smile that previously had not been appreciated. Imaging studies identified a frontal lobe tumor contralateral to her facial weakness. Thus the careful observation of seemingly subtle clinical findings may prove to have significant bearing on the issue at hand. Even when these findings are proven to be “normal variants,” clear documentation may often be very helpful during the course of the patient's illness or later on when new concerns occur. In that setting, the prior definition of what proves to be a normal asymmetry will prevent erroneous conclusions from being developed.

Formulation

One of the most intellectually challenging aspects of neurology relates to the neurologist's ability to amalgamate the historical and physical findings into a unitary hypothesis. One needs to first consider the multiple neuroanatomic sites that can potentially explain the patient's clinical presentation (Where is the lesion?). Subsequently, this is placed in the perspective of the patient's past medical and family history, as well as the clinical temporal profile of the symptom's occurrence (What is the etiology?). Did all of the patient's symptoms begin abruptly, as is usually seen with a stroke? Or was there an evolution of degree of clinical loss or did new features gradually get added to the patient's findings as is characteristic of certain neoplastic lesions and sometimes more diffuse vasculitides? Formulation can be hindered by the patient's inability to provide an accurate history or participate in the neurologic examination. One of the more subtle and difficult conditions to recognize is anosognosia to one's illness, as may occur in patients with right parietal brain injury. Under these circumstances, the patient may not have sensory, visual, or motor neglect, but unawareness of cognitive, emotional, and other functional limitations. Family interview is most important in this setting.

Overview and Basic Tenets

The neurologic examination begins the moment the patients get out of their seat to be greeted, the character of their smile or lack thereof, and subsequently as they walk to enter the neurologist's office. An excellent opportunity to judge the patient's language function and cognitive abilities occurs during the acquisition of the patient's history. Concurrently, the neurologist is always attuned to carefully making observations to identify various clinical signs. Some are overt movements (tremors, restlessness, dystonia, or dyskinesia); others are subtler, for example, vitiligo, implying a potential for a neurologic autoimmune disorder. Equally important may be the lack of normal movements, as seen in patients with Parkinson disease. By the time the neurologist completes the examination, she or he must be able to categorize and organize these historical and examination findings into a carefully structured diagnostic formulation.

The subsequent definition of the formal examination may be subdivided into a few major sections. Speech and language are assessed during the history taking. The cognitive part of the examination is often clearly defined with the initial history and often does not require formal mental status testing. However, there are a number of clinical neurologic settings where this evaluation is very time consuming and complicated; Chapter 25 is dedicated to this aspect of the patient evaluation.

Here the multisystem neurologic examination provides a careful basis for most essential clinical evaluations. Neurologists in training and their colleagues in practice cannot expect to test all possible cognitive elements in each patient they evaluate. Certain basic elements are required; most of these are readily observable or elicited during initial clinical evaluation. These include documentation of language function, affect, concentration, orientation, and memory. When concerned about the patient's cognitive abilities, the neurologist must elicit evidence of an apraxia or agnosia and test organizational skills. Once language and cognitive functions are assessed, the neurologist dedicates the remaining portion of the exam to the examination of many functions. These include cranial nerves (CNs) ( Fig. 1.1 ), muscle strength, muscle stretch reflexes (MSRs), plantar stimulation, coordination, gait, and equilibrium, as well as sensory modalities. These should routinely be examined in an organized fashion in order not to overlook an important part of the examination. The patient's general health, nutritional status, and cardiac function, including the presence or absence of significant arrhythmia, heart murmur, hypertension, or signs of congestive failure, should be noted. If the patient is encephalopathic, it is important to search for subtle signs of infectious, hepatic, renal, or pulmonary disease.

Fig. 1.1, Cranial Nerves: Distribution of Motor and Sensory Fibers.

Cranial Nerves: An Introduction

The 12 CNs subserve multiple types of neurologic function (see Fig. 1.1 ). The CNs are formed by afferent sensory fibers, motor efferent fibers, or mixed fibers traveling to and from brainstem nuclei ( Fig. 1.2 ).

Fig. 1.2, Cranial Nerves: Nerves and Nuclei.

The special senses are represented by all or part of the function of five different CNs, namely, olfaction, the olfactory (I); vision, the optic (II); taste, the facial (VII) and the glossopharyngeal (IX); and hearing and vestibular function, the cochlear and vestibular (VIII) nerves. Another three CNs are directly responsible for the coordinated, synchronous, and complex movements of both eyes; these include CNs III (oculomotor), IV (trochlear), and VI (abducens). CN VII is the primary CN responsible for facial expression, which is important for setting the outward signs of the patient's psyche's representation to his or her family and close associates, or signs of paralysis from a brain or CN lesion. Facial sensation is subserved primarily by the trigeminal nerve (V); however, it is a mixed nerve also providing primary motor contributions to mastication. The ability to eat and drink depends on CNs IX (glossopharyngeal), X (vagus), and XII (hypoglossal). The hypoglossal and recurrent laryngeal nerves are also important to the mechanical function of speech. Last, CN XI, the accessory, contains both cranial and spinal nerve roots that provide motor innervation to the large muscles of the neck and shoulder.

Disorders of the CNs can be confined to a single nerve such as the olfactory (from a closed-head injury, early Parkinson disease, or meningioma), trigeminal (tic douloureux), facial (Bell palsy), acoustic (schwannoma), and hypoglossal (carotid dissection). There is a subset of systemic disorders with the potential to infiltrate or seed the base of the brain and the brainstem at the points of exit of the various CNs from their intraaxial origins. These processes include leptomeningeal seeding of metastatic malignancies originating in the lung, breast, and stomach, as well as various lymphomas, or granulomatous processes such as sarcoidosis or tuberculosis, each leading to a clinical picture of multiple, sometimes disparate cranial neuropathies. Many times, a stuttering onset occurs. The various symptoms are related to individual CNs. These typically develop within just weeks or no more than a few months.

CN dysfunctions will commonly bring patients to medical attention for a number of clinical limitations. These include ophthalmic difficulties, such as diminished visual acuity or visual field deficits (optic nerve and pericavernous chiasm) and double vision, either horizontal, vertical, or skewed (oculomotor, trochlear, and abducens nerves). Other CN presentations include facial pain (trigeminal nerve), evolving facial weakness (facial nerve), difficulty swallowing (glossopharyngeal and vagus nerves), and slurred speech (hypoglossal nerves).

Cranial Nerve Testing

I: Olfactory Nerve

The sense of smell is a very important primordial function that is much more finely tuned in other animal species. Here, other mammals are able to seek out food, find their mates, and identify friend and foe alike because of their finely tuned olfactory brain. In the human, the loss of this function can still occasionally have very significant consequences primarily bearing on personal safety. If the human being cannot smell fires or burning food, their survival can be put at serious risk. The loss of smell also affects the pleasure of being able to taste, even though, as later noted, taste per se is primarily a function of CNs VII and IX.

Olfactory nerve function testing is relevant despite its only occasional clinical involvement. This may be impaired after relatively uncomplicated head trauma and in individuals with various causes of frontal lobe dysfunction, especially an olfactory groove meningioma. Loss of olfaction is sometimes an early sign of Parkinson disease. Clinical evaluation of olfactory functions is straightforward. The examiner has the patient sniff and attempt to identify familiar substances having specific odors (coffee beans, leaves of peppermint, lemon). Inability or reduced capacity to detect an odor is known as anosmia or hyposmia, respectively; inability to identify an odor correctly or smell distortion is described as parosmia or dysosmia. Bilateral olfactory nerve disturbance with total loss of smell, typically from head trauma, chronic upper airway infections, or medication, is usually a less ominous sign than unilateral loss, which raises the concern for a focal infiltrative or compressive lesion such as a frontal grove meningioma.

II: Optic Nerve

Of all the human sensations, the ability to see one's family and friends, read, and appreciate the beauties of nature is supreme; therefore it is difficult to imagine life without vision. Obviously, many individuals, such as Helen Keller, have vigorously and successfully conquered the challenge of being blind; however, given the choice, vision is one of the most precious of all animal sensations. “Blurred” vision is a common but relatively nonspecific symptom that may relate to dysfunction anywhere along the visual pathway ( Fig. 1.3 ). When examining optic nerve function, it is important to identify any concomitant ocular abnormalities such as proptosis, ptosis, scleral injection (congestion), tenderness, bruits, and pupillary changes.

Fig. 1.3, Visual Pathways: Retina to Occipital Cortex.

Visual acuity is screened using a standard Snellen vision chart that is held 14 inches from the eye. Screening must be performed in proper light, as well as to the patient's refractive advantage, using corrective lenses or a pinhole when indicated. A careful visual field evaluation is the other important means to assess visual function. These tests are complementary, one testing central resolution at the retinal level and the other to evaluate peripheral visual field defects secondary to lesions at the levels of the optic chiasm, optic tracts, and occipital cortex. Visual fields are evaluated by having the patient sit comfortably facing the examiner at a similar eye level. First, each eye is tested independently. The patient is asked to look straight at the examiner's nose. The examiner extends an arm laterally, equidistant from himself or herself and the patient, and asks the patient to differentiate between one and two fingers. The patient's attention must always be directed back to the examiner because most patients will reflexively look laterally at the fingers. This will require repeated testing. Each quadrant of vision is evaluated separately. After individual testing, both eyes are tested simultaneously for visual neglect, as may occur with right hemispheric lesions. Progressively complex perimetric devices have the advantage of providing valuable data on the health of the visual system.

In kinetic perimetry, a stimulus is moved from a nonseeing area (far periphery or physiologic blind spot) to a seeing area, with patients indicating at what point the stimulus is first noticed. Testing is repeated from different directions until a curve can be drawn connecting the points at which a given stimulus is seen from all directions. This curve is the isopter for that stimulus for that eye. The isopter plot has been likened to a contour map, showing “the island of vision in a sea of darkness.” The Goldmann perimeter, a half-sphere onto which spot stimuli are projected, is the premiere device for this mapping. The normal visual field extends approximately 90 degrees temporally, 45 degrees superiorly, 55 degrees nasally, and 65 degrees inferiorly. Practically, this geographic shape mimics the oblique teardrop shape of aviator-style sunglass lenses.

In static perimetry, the test point is not moved but turned on in a specific location. Typically automated, computer testing preselects locations within the central 30 degrees of field. Stimuli are dimmed until they are detected only intermittently on repetitive presentation—this intensity level is called the threshold. The computer then generates a map of numeric values of the illumination level required at every test spot, or the inverse of this level, often called a sensitivity value. Values may also be displayed as a grayscale map, and statistical calculations can be performed—by comparing to adjacent spots or precalculated normal values or noting sudden changes in sensitivity—to detect abnormal areas.

Most visual field changes have localizing value: specific location of the loss, its shape, or border sharpness (i.e., how quickly across the field the values change from abnormal to normal). Its concordance with the visual field of the other eye tends to implicate specific areas of the visual system. Localization is possible because details of anatomic organization at different levels predispose to particular types of loss (see Chapter 5 ).

When one examines the pupils, their shape and size need to be recorded. A side-to-side difference of no more than 1 mm in otherwise round pupils is acceptable as a normal variant. Pupillary responses are tested with a bright flashlight and are primarily mediated by the autonomic innervation of the eye ( Fig. 1.4 ). A normal pupil reacts to light stimulus by constricting with the contralateral constriction of the unstimulated pupil as well. These responses are called the direct and consensual reactions, respectively, and are mediated through parasympathetic innervation to the pupillary sphincter from the Edinger-Westphal nucleus along the oculomotor nerve. The pupils also constrict when shifting focus from a far to a near object (accommodation) and during convergence of the eyes, as when patients are asked to look at their nose.

The sympathetic innervation of the pupillary dilator muscle involves a multisynaptic pathway with fibers ultimately reaching intracranially along the course of the internal carotid artery. Branches innervate the eye after traveling through the long and short ciliary nerves. The ciliospinal reflex is potentially useful when evaluating comatose patients. In this setting, if the examiner pinches the patient's neck, the ipsilateral pupil should transiently dilate. This provides a means to test the integrity of ipsilateral pathways to midbrain structures.

The short ciliary nerve, supplying parasympathetic inputs to the pupil, may be damaged by various forms of trauma. This results in a unilateral dilated pupil with preservation of other third nerve function. Significant unilateral pupillary abnormalities are usually related to innervation changes in pupillary muscles.

A number of pathophysiologic mechanisms lead to mydriasis (pupillary dilatation) ( Table 1.1 ). Atropine-like eye drops, often used for their ability to produce pupillary dilation, inadvertent ocular application of certain nebulized bronchodilators, and placement of a scopolamine antimotion patch with inadvertent leak into the conjunctiva are occasionally overlooked as potential causes for an otherwise asymptomatic, dilated, poorly reactive pupil. Other medications may also lead to certain atypical light reactions. The presence of bilateral dilated pupils, in an otherwise neurologically intact patient, is unlikely to reflect significant neuropathology. In contrast, the presence of prominent pupillary constriction most likely reflects the use of narcotic analogs or parasympathomimetic drugs, such as those typically used to treat glaucoma.

TABLE 1.1

Pupillary Abnormalities

	Argyll Robertson	Horner	Holmes Adie
Response to light	None	Yes	None
Other responses	Brisk reaction to near stimulus Converge	Normal	Tonic reaction to near stimulus Accommodation
Margins	Irregular	Regular	Regular
Associated changes	Iris depigmentation	Ptosis	Loss of muscle stretch reflex
Causes	Tabes dorsalis	Carotid dissection Carotid aneurysm Pancoast tumor Syringomyelia	Ciliary ganglion
Anatomy	Unknown (tectum of midbrain likely)	Loss of sympathetic	Loss of parasympathetic

Horner Syndrome

The classic findings include miosis (pupillary constriction), subtle ptosis, and an ipsilateral loss of facial sweating. Here the constricted pupil develops secondary to interference with the sympathetic nerves at one of many different levels along its long intramedullary (brain and spinal cord) and complicated extracranial course.

Sympathetic efferent fibers originate within the hypothalamus and traverse the brainstem and cervical spinal cord, then exit the upper thoracic levels and course rostrally to reach the superior cervical ganglia (see Fig. 1.4 ). Subsequently, these sympathetic fibers track with the carotid artery within the neck to reenter the cranium and subsequently reach their destination innervating the eye's pupillodilator musculature. Typically, patients with Horner syndrome ( Fig. 1.5 ) have an ipsilateral loss of sweating in the face (anhidrosis), a constricted pupil (miosis), and an upper lid droop from loss of innervation to Müller muscle, a small smooth muscle lid elevator (ptosis). The levator palpebra superioris, a striated muscle innervated by the oculomotor nerve CN III, is not affected.

Optic Fundus

The ability to peer into the patient's eye is a very unique and fascinating experience because it provides an opportunity to directly examine not only the initial portion of the optic nerve but also tiny arterioles and veins. This is the only portion of human anatomy that provides the physician with such an opportunity. Here one may find signs of increased intracranial pressure or evidences of the effects of poorly controlled hypertension or diabetes mellitus. Currently all of these various lesions are much less commonly observed because of much better treatment of systemic illnesses that affect the smaller blood vessels. Similarly, the development of MRI and CT scanning makes it easier to identify intracerebral mass lesions at a much earlier stage of illness. Currently, as brain tumors no longer reach a critical size, obstructing cerebrospinal fluid flow, creating the increased intracranial pressure that leads to papilledema, this is now a relatively rare finding but one that still demands recognition.

A careful optic funduscopic examination is essential in the evaluation of very many neurologic disorders. This evaluation is best performed in a relatively dark environment that leads to both a reflex increase in pupillary size and improvement in contrast of the posterior chamber structures. Findings that should be documented include optic nerve margins, venous pulsations, and the presence of hemorrhages, exudates, or any obvious obstruction to flow by embolic material (such as cholesterol plaque in patients complaining of transient visual obscuration), and pallor of retinal fields that may reflect ischemia.

Papilledema is characterized by elevation and blurring of the optic disk, absence of venous pulsations, and hemorrhages adjacent to and on the disk ( Fig. 1.6 ). The finding of papilledema indicates increased intracranial pressure of any cause, including brain tumors, subarachnoid hemorrhage, metabolic processes, pseudotumor cerebri, and venous sinus thrombosis.

Fig. 1.6, Effects of Increased Intracranial Pressure on Optic Disk and Visual Fields.

III, IV, VI: Oculomotor, Trochlear, and Abducens Nerves

Our ability to acutely focus our eyes on an object of interest depends on being able to move the eyes together in a conjugate fashion; this requires three related CNs that take their origin from various juxta midline midbrain and pontine nuclei. These provide us with the ability to astutely focus on an object of interest without concomitantly moving our head. Whether it is a detective watching a suspect or a teenager taking a furtive glance at a new classmate, these CNs provide us with a broad sweep of very finely tuned motor function. There is no other group of muscles that is so finely innervated as these. Their innervation ratio is approximately 20:1, in contrast to those of large muscles of the extremities with ratios between 400:1 and 2000:1. Certainly, this accounts for the fact that one of the earliest clinical manifestations of myasthenia gravis relates to the extraocular muscles (EOMs), where the interruption of just a few neuromuscular junctions affects the finely harmonized EOM function, leading to a skewed operation and thus double vision.

To identify isolated EOM dysfunction, it is most accurate to test each eye individually, describing the observed specific loss of EOM function. For example, when the eye cannot be turned laterally, the condition is labeled as an abduction paresis, as opposed to CN VI palsy. This is because the responsible lesion can be at any one of three sites, namely, CN, neuromuscular junction, or muscle per se. A more detailed assessment of these CNs is available in Section II, Chapter 6 .

The medial longitudinal fasciculus (MLF) is responsible for controlling EOM function because it provides a means to modify central horizontal conjugate gaze circuits. The MLF connects CN III on one side and CN VI on the opposite side. Understanding the circuit of horizontal conjugate gaze helps clinicians to appreciate the relation between the frontal eye fields and the influence it exerts on horizontal conjugate gaze, as well the reflex relation between the ocular and vestibular systems ( Fig. 1.7 ).

The connection of the vestibular system to the MLF can be tested by two different means. One is the doll's-eye maneuver. Here the patient's head is rotated side to side while the examiner watches for rotation of the eyes. Passive movement of the head to the left normally moves the eyes in the opposite direction, with the left eye adducting and the right eye abducting. The opposite occurs when the head is rotated to the right.

Ice-water caloric stimulation provides another option to study vestibular ocular MLF pathways. This is primarily used for the examination of comatose patients; on very rare occasions, it is extremely helpful for rousing a patient presenting with a suspected nonorganic coma. Patients’ heads are placed at an elevation of approximately 45 degrees. Next, the tympanic membranes are checked for intactness, and then 25–50 mL of ice water is gradually infused into each ear. A normal response in the awake patient, after left ear stimulation, is to observe slow deviation of the eyes to the left followed by rapid movement (nystagmus) to the right (see Fig. 1.8 ). In contrast, the comatose patient with an intact brainstem has a persistent ipsilateral deviation of the eyes to the site of stimulation with loss of the rapid eye movement component to the opposite side.

Fig. 1.8, Vestibular Eighth Nerve Input to Horizontal Eye Movements and Nystagmus.

The center for vertical conjugate gaze and convergence is also located within the midbrain, although the underlying circuit is not well delineated. The vertical conjugate gaze centers can be tested by flexion of the neck while holding the eyelids open and watching the eye movements. When CNS processes affect conjugate gaze, such as with MS, a prominent nystagmus is often defined. The nystagmus is thought to result from an attempt to maintain conjugate function of the eyes and minimize double images.

V: Trigeminal Nerve

Our ability to perceive various stimuli applied to the face depends almost entirely on this nerve; whether as a warning to protect oneself from subzero cold, something potentially threatening to our eyesight, or the pleasurable sensation from the kiss of a beloved one, all forms of sensations applied to the face are tracked to our brain through the trigeminal nerve ( Fig. 1.9 ). The primary sensory portion of this nerve has three divisions, ophthalmic, maxillary, and mandibular; they respectively supply approximately one-third of the face from top to bottom, as well as the anterior aspects of the scalp. The angle of the jaw is spared within the trigeminal mandibular division lesions. This provides an important landmark to potentially differentiate patients with conversion disorders, because they are not anatomically sophisticated and may report they have lost sensation in this region.

The clinical testing of trigeminal nerve function includes both appreciation of a wisp of cotton and a sharp object on the facial skin, as well as the corneal reflex. To evaluate the broad spectrum of facial sensation (i.e., touch, pain, and temperature), the examiner uses a cotton wisp; the tip of a new, previously unused safety pin; and the cold handle of a tuning fork. In a symmetric fashion, the physician asks whether the patient can perceive each stimulus in the three major divisions of the trigeminal nerve supplying the face.

The corneal reflex depends on afferents from the first division of the trigeminal nerve combined with facial nerve efferents. This is also best tested using a wisp of cotton approaching the patient from the side while she or he looks away. Normally, both eyelids close when the cornea on one side is stimulated; this is because this reflex involves multisynaptic brainstem pathways.

Lastly, there is a primary motor portion that is part of the trigeminal nerve. It primarily supplies the muscles of mastication. It is best assessed by having the patient bite down and by trying to open the mouth against resistance.

VII: Facial Nerve

Facial expression is one of our very important innate human attributes, allowing one to demonstrate a very broad spectrum of human emotions, especially happiness and sorrow; these are primarily dependent on the facial nerve ( Fig. 1.10 ). The motor functions of CN VII are tested by asking patients to wrinkle their forehead, close their eyes, and smile. Whistling and puffing up the cheeks are other techniques to test for subtle weakness. When unilateral peripheral weakness affects the facial nerve after it leaves the brainstem, the face may look “ironed out,” and when the patient smiles, the contralateral healthy facial muscle pulls up the opposite half of the mouth while the affected side remains motionless. Patients often cannot keep water in their mouths, and saliva may constantly drip from the paralyzed side. With peripheral CN VII palsies, patients are also unable to close their ipsilateral eye or wrinkle their foreheads on the affected side. However, although the lid cannot close, the eyeball rolls up into the head, removing the pupil from observation. This is known as the Bell phenomena.

Fig. 1.10, Facial Nerve With Its Muscle Innervation.

In addition, there is another motor branch of the facial nerve; this innervates the stapedius muscle. It helps to modulate the vibration of the tympanic membrane and dampens sounds. When this part of the facial nerve is affected, the patient notes hyperacusis; this is an increased, often unpleasant perception of sound when listening to a phone with the ipsilateral ear.

Lastly, the facial nerve has a few other functions. These include prominent autonomic function, sending parasympathetic fibers to both the lacrimal and the salivary glands. It also subserves the important function of taste, another function providing both safety from rancid food and pleasure from a delightful wine. There is also a tiny degree of routine skin sensation represented for portions of the ear.

VIII: Cochlear and Vestibular Nerves (Auditory Nerve)

Many mornings some of us are blessed by a virtual ornithologic symphony in our backyards. This always makes one pause and give thanks once again for this marvelous primary sensation. Here, yet another CN, the cochlear, provides for the emotional highs that auditory sensations bring to the human brain. Whether it is the first cry of a newborn, the reassuring words of a loved one, or Beethoven's seventh symphony, this unique sensation of higher animal life is tracked through this one CN.

Beyond the simple test of being able to hear, more sophisticated clinical evaluation of CN VIII is often challenging for the neurologist. Fortunately, our otolaryngologist colleagues are able to precisely measure the appreciation of specific auditory frequencies in a very sophisticated manner. Barring the availability of these formal audiometric evaluations, simple office-based hearing tests sometimes help to demonstrate diagnostically useful asymmetries. Using a standard tuning fork, it is possible to differentiate between nerve (perceptive) deafness caused by cochlear nerve damage and that caused by middle ear (conduction) deafness, with two different applications of the standard tuning fork. We are able to test both air and bone conduction.

Initially a vibrating tuning fork is placed on the vertex of the skull, Weber test, allowing bone conduction to be assessed. Here the patient is asked to decide whether one ear perceives the sound created by the vibration better than the other ( Fig. 1.11 ). If the patient has nerve deafness, the vibrations are appreciated more in the normal ear. In contrast, with conduction deafness, the vibrations are better appreciated in the abnormal ear.

Fig. 1.11, Auditory Nerve Testing: Weber and Rinne Testing.

The Rinne test is carried out by placing this vibrating instrument on the mastoid process of the skull. Here the patient is asked to identify the presence of sound. As the vibrations of the tuning fork diminish, eventually the patient is unable to appreciate the sound. At that instant, the instrument is moved close to the external ear canal to evaluate air conduction. If the individual has normal hearing, air conduction is longer than bone conduction. When a patient has nerve (perceptive) deafness, both bone and air conductions are diminished, but air conduction is still better than bone conduction. In contrast with conduction deafness, secondary to middle ear pathology, these findings are reversed. Here, when the patient's bony conduction has ceased, air conduction is limited by the intrinsic disorder within the middle ear. Therefore the sound can no longer be heard; that is, it cannot pass through the mechanoreceptors that amplify the sound and thus cannot reach the auditory nerve.

Vestibular Nerve

The vestibular system can be tested indirectly by evaluating for nystagmus during testing of ocular movements or by positional techniques, such as the Barany maneuver (aka Dix-Hallpike test), that induce nystagmus in cases of benign positional vertigo (BPV) in which inner ear dysfunction is caused by otolith displacement into the semicircular canals ( Fig. 1.12 ). Here the patient is seated on an examining table and the eyes are observed for the presence of spontaneous nystagmus. If none is present, the examiner rapidly lays the patient back down, with the head slightly extended and concomitantly turning the head laterally. If, after a few seconds’ delay, the patient develops the typical symptoms of vertigo with a characteristic delayed rotary, eventually fatiguing nystagmus, the study is positive.

Eye movements depend on two primary components, the induced voluntary frontal eye fields and the primary reflex-driven vestibular-ocular movement controlled by multiple connections (see Fig. 1.8 ; and also Fig. 1.7 ). The ability to maintain conjugate eye movements and a visual perspective on the surrounding world is an important brainstem function. It requires inputs from receptors in muscles, joints, and the cupulae of the inner ear. Therefore, when the patient has dysfunction involving any portion of the vestibular-ocular or cerebellar axis, the maintenance of basic visual orientation is challenged. Nystagmus is a compensatory process that attempts to help maintain visual fixation.

Traditionally, when one describes nystagmus, the fast phase direction becomes the designated title (see Fig. 1.8 ). For example, left semicircular canal stimulation produces a slow nystagmus to the left, with a fast component to the right. As a result, the nystagmus is referred to as right beating nystagmus. Direct stimulation of the semicircular canals or its direct connections (i.e., the vestibular nuclei) often induces a torsional nystagmus. This is described as clockwise or counterclockwise, according to the fast phase.

A few beats of horizontal nystagmus occurring with extreme horizontal gaze is normal in most individuals. The most common cause of bilateral horizontal nystagmus occurs secondary to toxic levels of alcohol ingestion or some medications (i.e., phenytoin and barbiturates).

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