Disorders of Mental Status

Apraxia: Neurology of Learned Movement

Apraxia is a disorder of learned motor acts not caused by paralysis, incoordination, sensory deficit, or lack of understanding of the desired movement. In practical terms, apraxia is an inability to carry out skilled motor acts to respond to a command when the patient understands the command and can perform the same motor act in a different context. Liepmann, a German clinician, described three types of apraxia: ideomotor, ideational, and limb kinetic.

It is important to differentiate several diverse motor phenomena that are commonly confused with the principal varieties of apraxia. These are constructional, dressing, oculomotor, and gait apraxia.

Constructional apraxia , characterized by visuospatial difficulties, is associated with right hemispheric lesions. These patients may be unable to copy a drawing of a clock or a house. In most instances, this deficit is related to neglect of the left side of space or failure to appreciate the spatial relations of items rather than to a motor planning deficit, hence apraxia may not be the best name for it.

Dressing apraxia is also associated with right hemisphere lesions. The patients have difficulty relating the spatial aspects of a garment to the body. Again, this is a visuospatial deficit and not a true motor apraxic deficit.

Oculomotor apraxia refers to a difficulty with voluntary direction of the eyes in gaze and is associated with damage to the brainstem mechanism for control of eye movements.

Gait apraxia refers to an inability to walk that is not clearly explained by primary motor weakness, ataxia, or sensory loss. There is no easy way to demonstrate that the same sequential actions can be performed normally in a different context; therefore, it is unclear whether this gait disorder is a true apraxia.

A last example is apraxia of speech , discussed in Chapter 5.2 . Whether apraxia of speech is a true apraxia is debated by aphasia experts.

Agnosias: Neurology of Recognition

Agnosias are disorders of recognition. Most affect a single sensory system (visual, auditory, or tactile agnosia), and others involve specific classes of items within a modality (prosopagnosia which is agnosia for faces and phonagnosia which is agnosia for familiar voices). In each case, the patient must be shown to have normal primary sensory perception, normal ability to name the item once it is recognized, and no general cognitive deterioration or dementia.

For example, a patient with visual agnosia may fail to recognize a bell by sight but can identify and name it by the sound of the bell ringing or by palpating it. Each sensory modality carries a somewhat arbitrary division between primary sensory cortical deficits and agnosia. Most agnosias require bilateral cortical lesions, cutting off input from the sensory modality in both hemispheres to the left hemisphere language centers.

In the visual system, bilateral occipital lesions may cause cortical blindness; partial lesions may permit primary visual perception of the elements of an object or picture, such that the patient can draw lines or angles representing the item but cannot identify the item. Shown a drawing of a pair of glasses, the patient may report two circles and identify it as a bicycle.

Prosopagnosia, or the inability to identify faces, is a subtype of visual agnosia in which patients cannot recognize family members or friends, although they can describe features, such as hair color, a mustache or beard, or accessories (e.g., hats or glasses). Frequently, the patient with prosopagnosia identifies the person by voice or gait pattern. Oliver Sacks described prosopagnosia, or perhaps a more profound visual agnosia, in The Man Who Mistook His Wife for a Hat .

Auditory agnosias also overlap with the syndrome of cortical deafness resulting from bilateral lesions of the temporal cortex. Some patients with bilateral temporal lobe lesions have preserved pure tone hearing but cannot understand spoken language. As discussed in Chapter 5.2 , this deficit is referred to as pure word deafness. Geschwind suggested that pure word deafness results from a bilateral disconnection of the input from the primary auditory cortex (Heschl gyrus) to the left hemisphere Wernicke area. Rarely, patients show preserved auditory comprehension but impaired nonverbal auditory recognition, for example, identification of animal sounds or the characteristic sounds associated with an object such as a bell. This deficit is called auditory nonverbal agnosia. A last bitemporal syndrome is phonagnosia, the inability to recognize familiar voices.

In the tactile modality, parietal lesions often disrupt the identification of objects by feel, a deficit called astereognosis. A related deficit, agraphesthesia, involves the inability to recognize letters or numbers drawn on the hand. If the patient can describe the sensory characteristics of an object but not identify it, this can also qualify as tactile agnosia. In rare instances, patients with bilateral parietal lesions have no ability to recognize objects by touch on either side.

Delirium

No disorder in neurology is more striking or more distressing to patients, families, and medical personnel than delirium or acute encephalopathy. Delirium is second only to stroke as a cause for neurologic consultation Vanderbilt University Medical Center.

Delirium is defined as “a transient disorder of cognition and attention, one accompanied by disturbances of the sleep–wake cycle and psychomotor behavior.” Multiple cognitive functions are affected in disparate areas of the brain.

Delirium typically involves alterations in the following features, although not all of them are seen in all patients or at once:

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  Disturbed level of consciousness

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    Somnolence

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    Hypervigilance

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    Agitation

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  Disturbed perception

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    Hallucinations

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    Illusions

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    Delusions

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  Psychomotor abnormalities

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    Restlessness

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    Agitation

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    Disturbed sleep–wake cycle

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  Autonomic nervous system hyperactivity

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    Tachycardia

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    Hypertension

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    Fever

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    Diaphoresis

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    Tremor

In current usage, the term delirium can be diagnosed when the patient is agitated, in a normal state of alertness, or somnolent.

Delirium is a common neurobehavioral syndrome, occurring in 30% to 50% of hospitalized patients over age 70. Because almost 50% of hospitalized patients are elderly, it is estimated that as many as 10% of hospitalized medical and surgical patients are encephalopathic at any given time. Though delirium often resolves over days to weeks, a substantial proportion of patients have ongoing cognitive deficits.

A number of specific risk factors for delirium have been identified:

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  Preexisting cognitive deficits

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  Age older than 80 years

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  Prior brain disorder

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  Hearing loss

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  Vision loss

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  Fracture on admission

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  Symptomatic infection

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  Stress

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  Environmental changes

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  Medications including

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    Neuroleptics

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    Narcotic analgesics

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    Sedatives

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    Anticholinergic drugs

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  Medical procedures including

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    Use of restraints

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    Bladder catheterization

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    Surgery