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Hemiplegia and Monoplegia
Hemiplegia and monoplegia are more likely to be due to discrete focal lesions than diffuse lesions, so these presentations are especially suited to clinical-anatomical localization. Similarly, imaging studies are likely to be revealing with hemiplegia or monoplegia, but the focus of imaging must be directed by clinical suspicion.
Hemiplegia and monoplegia are motor symptoms and signs; however, associated sensory abnormalities are essential to localization, so these are discussed when appropriate. Sensory deficit syndromes are discussed in more depth in Chapter 31 . Motor power begins with volition, the conscious effort to initiate movement. Lack of volition does not produce weakness but rather results in akinesia. Projections from the premotor regions of the frontal lobes to the motor strip result in activation of corticospinal tract (CST) neurons, which then have a descending pathway, which is detailed later.
Localization begins with identification of weakness. Differentiation is made among the following distributions:
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Generalized weakness
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Monoplegia
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Hemiplegia
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Paraplegia
Only hemiplegia and monoplegia are discussed in this chapter.
Anatomy and Physiology
Motor System Anatomy
Anatomical localization begins with a good understanding of anatomy and physiology. Focal deficits such as hemiplegia and monoplegia are more likely to be due to a focal structural lesion than diffuse disorders, so anatomy is of prime importance.
The neuroanatomical locus of motor initiative is unknown and likely diffuse, but motor planning probably begins in the premotor cortex. Integrating sensory information into the planning stage, neurons of the premotor cortex project widely to targets including the motor cortex, prefrontal cortex, parietal cortex, supplementary motor cortex area, basal ganglia, thalamus, and spinal cord. Output from the primary motor cortex descends through the internal capsule to the brainstem and spinal cord as the pyramidal tract.
Pyramidal Tract
Pyramidal tract axons become the corticobulbar and corticospinal tracts. Most of the descending axons cross in the brainstem to activate contralateral cranial nerve nuclei or descend into the spinal cord in the lateral corticospinal tract. These neurons generally supply limb muscles. A minority of the motor axons descend in the spinal cord uncrossed in the anterior corticospinal tract, where some of these axons cross before they supply contralateral motoneurons. Some of the descending neurons that are uncrossed supply ipsilateral axial muscles.
The premotor cortex is divided into divisions that have cytoarchitectural foundations and some functional implications, but real topographic organization develops in the primary motor cortex, where mapping of the body areas served by regions of the cortex produces a distorted representation of the body—the homunculus ( Fig. 26.1 ).
Descending corticospinal pathways through the internal capsule are topographically organized, though not as precisely as in the motor cortex. Within the internal capsule, the corticospinal tracts are generally in the posterior limb, with the face and arm axons anteriorly and the leg axons posteriorly.
As the corticospinal axons descend through the spinal cord, the presence of crossed and uncrossed axons makes for complex effects of lesions on motor function. In addition, whereas there is some topographic organization to the corticospinal tracts, this is not as precise or clinically relevant as in the motor cortex or even internal capsule ( ).
Basal Ganglia
The basal ganglia likely modulate motor activity rather than directly activating it. They seem to play a role in control of initiation of movement by the premotor and motor cortical regions. In addition to the role of the basal ganglia in motor function, they are implicated in other functions, including memory and particularly the initiation, execution, and termination of learned motor tasks ( ). There is also evidence of involvement of the basal ganglia in nonmotor cognitive tasks ( ).
Afferents to the basal ganglia are from the cerebral cortex and thalamus to the striatum. Efferents from the striatum are largely to the globus pallidus and substantia nigra. The globus pallidus, in turn, projects to the thalamus.
Cerebellum
The cerebellum monitors and modulates motor activities, responding to motor commands and inputs from sensory receptors of the joints, muscles, and vestibular system. The cerebellum is somewhat topographically organized, with gait and axial musculature represented at and near the midline and limb motor activity served laterally in the cerebellar hemispheres.
Localization of Motor Deficits
The topographic organization of the cerebral cortex dictates that lesions produce weakness depending on location and size. The homunculus roughly predicts which muscles are affected. If the lesion is small and localized to the motor cortex, the deficit can be purely or solely motor. If the lesion is larger and involves sensory regions, a sensory deficit is expected.
Lesions of the internal capsule can potentially involve only motor axons; but because of the proximity of adjacent structures, some sensory involvement is more common. Lesions producing limited motor involvement of one limb are not commonly associated with the internal capsule.
Lesions of the descending corticospinal tracts in the brainstem produce hemiplegia, typically with other brainstem signs, such as crossed sensory symptoms, cranial nerve deficits, or ataxia not explained by weakness.
Lesions of the corticospinal tract in the spinal cord usually produce upper motoneuron (UMN) deficits below the level of the lesions but also often lower motoneuron (LMN) deficits at the level of the lesion. Lesions so restricted in the cord as to produce hemiparesis or the Brown-Séquard syndrome are rare.
Lesions and disorders of the basal ganglia commonly produce contralateral motor dysfunction, although they are more likely to manifest as difficulty with motor control rather than hemiplegia or monoplegia. Disorders with focal motor symptoms from basal ganglia dysfunction include Parkinson disease, dystonia, hemiballismus, and Huntington disease.
Lesions of the cerebellum do not produce hemiplegia or monoplegia. Instead, a lateral lesion will produce ipsilateral limb ataxia and a midline lesion gait ataxia.
Hemiplegia
Cerebral Lesions
Cerebral lesions constitute the most common cause of hemiplegia. Lesions in either cortical or subcortical structures may be responsible for the weakness ( Table 26.1 ). Some lesions are both cortical and subcortical, and some these can include mass lesions, infarctions, and hemorrhages.
TABLE 26.1
Cerebral Lesions
| Lesion Location | Symptoms | Signs |
|---|---|---|
| Motor cortex | Weakness and poor control of the affected extremity, which may involve face, arm, and leg to different degrees | Incoordination and weakness that depends on the location of the lesion within the cortical homunculus; often associated with neglect, apraxia, aphasia, or other signs of cortical dysfunction |
| Internal capsule | Weakness that usually affects the face, arm, and leg almost equally | Often associated with sensory impairment in same distribution |
| Basal ganglia | Weakness and incoordination on the contralateral side | Weakness, often without sensory loss; no neglect or aphasia |
| Thalamus | Sensory loss | Sensory loss with little or no weakness |
Cortical Lesions
Cortical lesions produce weakness that is more focal than the weakness seen with subcortical lesions. Fig 26.1 is a diagrammatic representation of the surface of the brain, showing how the body is mapped onto the surface of the sensorimotor cortex: the homunculus. The face and arm are laterally represented on the hemisphere, whereas the leg is draped over the top of the hemisphere and into the interhemispheric fissure.
Small lesions of the cortex can produce prominent focal weakness of one area, such as the leg or the face and hand; but hemiplegia—paralysis of both the leg and arm on the same side of the body—is not expected from a cortical lesion unless the damage is extensive. The most likely cause of cortical hemiplegia would be a stroke involving the entire territory of the internal carotid artery.
Seizure-related weakness
Seizures can present with hemiparesis due either to ictal paralysis or postictal (Todd) paralysis. The latter is much more common than the former.
Todd paralysis
Postictal (Todd) paralysis is a transient weakness that develops contralateral to the seizure focus. The preceding motor activity is followed by weakness lasting from minutes to hours, as long as 36 hours, with a median duration of about 15 hours ( ). Depending on the anatomy of the distribution of the seizure activity, nonmotor manifestations such as aphasia may occur, although aphasia can be ictal as well as postictal ( ).
There is no specific diagnostic test, but with prolonged hemiparesis after a seizure, electroencephalography (EEG) is often indicated to rule out nonconvulsive status epilepticus. If the patient has no history of seizures, particularly focal seizures, emergent evaluation for acute stroke is warranted because both ischemic and hemorrhagic stroke can present with seizure activity ( ).
Ictal paralysis
Ictal paralysis is weakness due to the discharge rather than the after effects of the discharge, as with Todd paralysis ( ). This is much less common. It can be confused with stroke, and some patients with ictal paralysis may be treated with reperfusion therapy for acute ischemic stroke ( ). Luckily, the risk of these treatments is relatively low in patients without an acute stroke ( ). Ictal paralysis is seen mainly in children, making confusion with stroke less likely.
Diagnosis of ictal paralysis depends on obtaining an EEG during the episode. EEG often shows slow-wave activity. Periodic lateralized epileptiform discharges (PLEDs) have also been described ( ).
Alternating hemiplegia of childhood
Alternating hemiplegia of childhood is a rare condition characterized by attacks of unilateral weakness, often with signs of other motor deficits (e.g., dyskinesias, stiffness) and oculomotor abnormalities (e.g., nystagmus) ( ). Attacks begin in early childhood, usually before age 18 months; they last hours and deficits accumulate over years. Initially patients exhibit normal neurological function between attacks, but with time persistent neurological deficits become obvious. A benign form can occur on awakening in patients who are otherwise normal and do not develop progressive deficits; this entity is related to migraine. Diagnostic studies are often performed, including magnetic resonance imaging (MRI), EEG, and angiography, but these usually show no abnormalities. Alternating hemiplegia is suggested when a young child presents with episodes of hemiparesis, especially on awakening, not associated with headache.
Hemiconvulsion-hemiplegia-epilepsy syndrome
In young children with the rare condition called hemiconvulsion-hemiplegia-epilepsy syndrome, unilateral weakness develops after the sudden onset of focal seizures. The seizures are often incompletely controlled. Neurological deficits are not confined to the motor system and may include cognitive, language, and visual deficits. Unlike alternating hemiplegia, the seizures and motor deficits are initially consistently unilateral, although eventually the unilateral seizures may become generalized. Imaging findings may be normal initially but eventually atrophy of the affected hemisphere is seen ( ). Cerebrospinal fluid (CSF) analysis is not specific, but a mild mononuclear pleocytosis may develop because of central nervous system (CNS) damage and seizures. Rasmussen encephalitis is a cause of this syndrome.
Subcortical Lesions
Subcortical lesions are more likely than cortical lesions to produce equal weakness of the contralateral face, arm, and leg because of the convergence of the descending axons in the internal capsule. The internal capsule is a particularly common location for lacunar infarctions and can also be affected by hemorrhage in the adjacent basal ganglia or thalamus. Weakness of sudden onset is most likely to be the result of infarction, with hemorrhage in a minority of cases. Demyelinating disease is characterized by a subacute onset. Tumors are associated with a slower onset of deficit and can grow quite large in subcortical regions before the patient presents for medical attention.
Infarction
Infarction is usually a clinical diagnosis but can be confirmed by computed tomography (CT) or MRI, as discussed earlier (see “Cortical Lesions”). Infarction manifests with an acute onset of deficit, although the course may be one of steady progression or stuttering. Lacunar infarctions are more likely than cortical infarctions to be associated with a stuttering course.
Lenticulostriate arteries
Lenticulostriate arteries are small penetrating vessels that arise from the proximal middle cerebral artery (MCA) and supply the basal ganglia and internal capsule. Infarction commonly produces contralateral hemiparesis with little or no sensory involvement. This is one cause of the syndrome of pure motor stroke, which can also be due to a brainstem lacunar infarction ( ).
Thalamoperforate arteries
These are small penetrating vessels that arise from the posterior cerebral artery (PCA) and supply mainly the thalamus. Infarction in this distribution produces contralateral sensory disturbance but can also cause movement disorders such as choreoathetosis or hemiballismus; hemiparesis is not expected.
Leukoencephalopathies
Multiple sclerosis
MS manifests with any combination of deficits due to white matter dysfunction. Hemiparesis can develop, especially if large plaques affect the CST fibers in the hemispheres. Hemiparesis is even more likely with brainstem or spinal demyelinating lesions because small lesions in these areas can produce more profound deficits. The diagnosis is suggested by progression over days plus a prior history of episodes of relapsing and remitting neurological deficits. Episodes of weakness that last for only minutes are unlikely to be due to demyelinating disease but rather to a transient ischemic attack (TIA), migraine equivalent, or seizure.
Diagnosis is based on clinical grounds for most patients, but the finding of areas of increased signal intensity on MRI T2-weighted images is suggestive of MS. Active demyelinating lesions often show enhancement on gadolinium-enhanced T1-weighted images. CSF examination is usually performed and can show normal findings or elevated protein, a mild lymphocytic pleocytosis, or oligoclonal bands of immunoglobulin G (IgG).
Progressive multifocal leukoencephalopathy
Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease caused by reactivation of the JC virus, usually seen in immunodeficient patients. Predisposed patients include those with acquired immunodeficiency syndrome (AIDS), leukemia, lymphoma, tuberculosis, or sarcoidosis. Patients receiving immunosuppressive therapies—such as natalizumab, rituximab, cyclophosphamide, or cyclosporine for various autoimmune diseases—are also at risk. Visual loss is the most common presenting symptom, and weakness is the second. MRI shows multiple white matter lesions. CSF either reveals no abnormality or shows a lymphocytic pleocytosis or elevated protein, or both. Brain biopsy is required for specific diagnosis, although JC virus deoxyribonucleic acid (DNA) can be detected in the CSF by polymerase chain reaction (PCR) assay in most patients. PML is suggested when a patient with immunodeficiency presents with subacute to chronic onset of neurological deficits and multifocal white matter lesions on MRI.
Although there are no proven treatments, general principles can be applied—namely, improving immunological status by the treatment of underlying disease and the removal of immunosuppressive therapies. Caution should be taken when discontinuing immunosuppressants, since recovery of the immune system can lead to immune reconstitution inflammatory syndrome (IRIS) and consequently to worsening neurological status. IRIS can be managed with a short course of high-dose intravenous corticosteroids. Natalizumab-induced PML can be managed by plasma exchange.
Both cortical and subcortical
Infections
Infections can present as hemiplegia, usually with a subacute onset. Bacterial abscess of the brain can present with subacute progressive hemiparesis. This can occur in isolation, from dental or other sources, or in the bed of an infarction, as in a patient with bacterial endocarditis ( ). With acute onset of weakness and then progressive worsening, embolic infarction and then abscess in the region of the infarction has to be considered.
Viral infections such as encephalitis can present with hemiplegia but usually are associated with other symptoms. Hemiparesis from herpes simplex virus (HSV) encephalitis would be expected to be associated with fever, mental status changes, headache, and/or seizures ( ).
Migraine
Migraine has many subdivisions, and the classification scheme is evolving. Among the subdivisions in the 2013 scheme ( ) are the following:
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Migraine without aura
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Migraine with aura, including typical aura, hemiplegic migraine, brainstem aura, and retinal migraine
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Chronic migraine
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Complications of migraine, including migrainous infarction, persistent aura without infarction, and aura-triggered seizure
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Probable migraine
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Episodic syndromes that may be associated with migraine
Many of these can cause hemiplegia ( ). Migraine without aura is episodic headache without aura; by definition, there should be no deficit. Migraine with aura is episodic headache with aura, most commonly visual. The subtypes of hemiplegic migraine, brainstem aura, and retinal migraine all have associated neurological deficit, but hemiplegia is typical of only the first subtype. Hemiplegic migraine , as its name suggests, is characterized by paralysis of one side of the body, typically with onset before the headache; this variant is often familial. Migraine with brainstem aura is episodic headache with brainstem signs including vertigo and ataxia; this variant is a disorder mainly of childhood. Migrainous infarction features sustained deficit plus MRI evidence of infarction that had developed from the migraine. Definitive diagnosis is problematic because patients with migraine have a higher incidence of stroke not associated with a migraine attack. Persistent aura without infarction is persistence of the aura for a week or longer without evidence of infarction on MRI.
The diagnosis of migraine is suggested by the combination of young age of the patient with few vascular risk factors and a marching deficit that can be conceptualized as migration of spreading electrical depression across the cerebral cortex. Imaging is often necessary to rule out hemorrhage, infarction, and demyelinating disease.
Mass lesion
Although infarction presents with deficits with localization dependent on vascular anatomy, mass lesions are not so constrained. Lesions may affect motor and sensory systems with complex symptomatology. The etiology of these nonvascular cortical lesions is usually trauma, tumor, or infection. Diagnosis of acute trauma is typically easy but identification of the remote effects of trauma may be difficult, especially when limited history is available.
Hemiplegia from mass lesion can be produced by a large lesion of the cerebral hemisphere, at which point nonmotor symptoms would be evident, including cortical signs, sensory abnormalities, and/or visual field abnormalities. Subcortical mass lesions are seldom as restricted to internal capsule/basal ganglia as infarction.
Infarction
Both cortical and subcortical infarctions can produce weakness, but cortical infarctions are more likely than subcortical infarctions to be associated with sensory deficits. Also, many cortical infarctions are associated with cortical signs—neglect with nondominant hemisphere lesions and aphasia with dominant hemisphere lesions. Unfortunately this distinction is not absolute because subcortical lesions can also occasionally produce these signs.
Initial diagnosis of infarction is usually made on clinical grounds. An abrupt onset of the deficit is typical. Weakness that progresses over several days is unlikely to be caused by infarction, although some infarcts can show worsening for a few days after onset. Progression over days suggests demyelinating disease or infection. Progression over weeks suggests a mass lesion such as tumor. Progression over seconds to minutes in a marching fashion suggests either epilepsy or migraine; not all migraine-associated deficits are associated with concurrent or subsequent Headache.
Head CTs often do not show infarction for up to 3 days after the event but are performed emergently to rule out mass lesion or hemorrhage. Small infarctions may never be seen on CT. MRI is superior in showing both old and new infarctions; diffusion-weighted imaging (DWI) in conjunction with apparent diffusion coefficient (ADC) on MRI distinguishes recent infarction from old lesions.
Middle cerebral artery
The MCA supplies the lateral aspect of the motor sensory cortex, which controls the face and arm. On the dominant side, speech centers are also supplied—the Broca area (expression) in the posterior frontal region and the Wernicke area (reception) on the superior aspect of the temporal lobe.
Cortical infarction in the territory of the MCA produces contralateral hemiparesis, which is usually associated with other signs of cortical dysfunction such as aphasia with left hemispheric lesions or neglect with right hemispheric lesions. Weakness is much more prominent in the arm, hand, and face than in the leg. Hemianopia is sometimes seen, especially with large MCA infarctions, as a result of infarction of the optic radiations. MCA infarction is suspected with hemiparesis plus cortical signs of aphasia or neglect. Confirmation is with imaging.
Anterior cerebral artery
The ACA supplies the inferior frontal and parasagittal regions of the frontal and anterior parietal lobes. This region is responsible for leg movement and is important for bowel and bladder control. Infarction in the ACA distribution produces contralateral leg weakness. The arm may be slightly affected, especially the proximal arm, with sparing of hand and face. In some patients, both ACAs arise from the same trunk, so infarction produces bilateral leg weakness; this deficit can be mistaken clinically for myelopathy and is in the differential diagnosis for suspected cord infarction or other acute myelopathy.
ACA infarction is suggested by a clinical presentation of unilateral or bilateral leg weakness and CST signs. Confirmation is with MRI.
Posterior cerebral artery
The PCAs are the terminal branches of the basilar artery. They supply most of the occipital lobes and the medial aspect of the temporal lobes. PCA infarction is not expected to produce weakness but produces contralateral hemianopia, often with memory deficits due to bilateral hippocampal infarction.
The clinical diagnosis of PCA infarction may be missed because an examiner may not look for hemianopia in a patient who otherwise presents only with confusion. Visual complaints may be vague or nonexistent.
PCA infarction is suggested by a clinical presentation of acute confusion, visual disturbance, or both. A finding of hemianopia is supportive evidence. Imaging can show not only the area of infarction but also the location of the vascular defect—unilateral or bilateral PCA or basilar artery.
Hemorrhages
A wide range of intracranial hemorrhages (ICHs) can produce hemiparesis. The development of ICH, as opposed to infarction, is suggested especially by drowsiness, seizures, and progression of the deficit. CT of the brain promptly makes the diagnosis in most circumstances. Occasionally small subdural hematomas (SDHs) may not be seen on CT but are seen on MRI and may produce hemiparesis.
Hemorrhages are of the multiple types: intraparenchymal hemorrhage (IPH), subdural hemorrhage (SDH), epidural hemorrhage (EDH), intraventricular hemorrhage (IVH), and subarachnoid hemorrhage (SAH).
Intraparenchymal hemorrhage
IPH is often hypertensive and may be predisposed by a vascular malformation. Trauma can produce IPH, but there are usually other associated ICHs with this. Associated IVH, SDH, and SAH are common. Hemiparesis can be produced especially by IPH and SDH.
Subarachnoid hemorrhage
Nontraumatic SAH predisposes to the development of vasospasm and infarction, resulting in hemiplegia. This is discussed in detail in Chapter 67 . Traumatic brain injury is associated with an increased risk of subsequent stroke and resultant hemiparesis, but traumatic SAH does not seem to enhance this risk ( ).
Subdural hematoma
Subdural hematoma is often associated with hemiparesis, and the presence of this deficit is one indicator of whether surgical intervention is needed ( ). The exact mechanism of hemiparesis under a subdural hematoma is not known, but recent data suggest that mechanical tension on the cortex is a strong correlate and likely a larger determinant than actual SDH size ( ).
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