CHAPTER 10

Agnosia, Apraxia, and Related Disorders of Higher Cortical Function

Gnosia (Gr. gnosis, “knowledge”) refers to the higher synthesis of sensory impulses, with the resulting perception, appreciation, and recognition of stimuli. Agnosia refers to the loss or impairment of the ability to know or recognize the meaning or import of a sensory stimulus, even though it has been perceived. Agnosia occurs in the absence of any impairment of cognition, attention, or alertness. The patients are not aphasic and do not have word-finding or a generalized naming impairment. Hughlings Jackson saw agnosia as a nonlanguage form of aphasia. Agnosias are usually specific for a given sensory modality and can occur with any type of sensory stimulus. Agnosias that involve the primary sensory modalities may represent disconnection syndromes that disrupt communication between a specific cortical sensory area and the language areas, which causes a restricted anomia. Agnosias are frequently due to bilateral or diffuse processes such as multiple stroke, hypoxic ischemic encephalopathy, and degenerative disorders.

Tactile agnosia refers to the inability to recognize stimuli by feel; visual agnosia is the inability to recognize visually; and auditory (acoustic) agnosia is the inability to know or recognize by audition. Body-image agnosia (autotopagnosia) is loss or impairment of the ability to name and recognize body parts. Finger agnosia is a type of autotopagnosia involving the fingers. Auditory agnosia is the loss of recognition of sounds. A patient with auditory agnosia may not be able to distinguish between the sound of a baby crying and the noise of traffic. Phonagnosia is the loss of recognition of familiar voices. Amusia is a form of auditory agnosia (Chapter 9). Time agnosia refers to loss of time sense without disorientation in other spheres. Visuospatial agnosia is loss or impairment in the ability to judge direction, distance, and motion and the inability to understand three-dimensional spatial relationships. Because of the impaired spatial judgment and visual disorientation, the patient cannot find her way in familiar surroundings. Multimodal agnosias may occur with dysfunction of the association areas in the parietal and temporal lobes that assimilate sensory information from more than one domain.

Astereognosis (stereoanesthesia) is loss of the ability to recognize and identify an object by touch despite intact primary sensory modalities. There is no loss of perceptual ability. The patient can feel the object, sensing its dimensions, texture, and other relevant information. However, she is unable to synthesize this information and correlate it with past experience and stored information about similar objects in order to recognize and identify it. Stereognosis is tested by asking the patient to identify, with eyes closed, common objects placed into the hand (e.g., coin, key, button, safety pin, paper clip). The most convincing deficit is when the patient is able to identify with the other hand an object that she was unable to identify with the tested hand. When primary sensory modalities in the hand are impaired, as by radiculopathy or neuropathy, failure to identify an object by touch is not astereognosis. Astereognosis usually indicates a lesion involving the contralateral parietal lobe. Rarely, a lesion of either parietal lobe can produce astereognosis bilaterally. It has also been reported to occur with lesions involving the anterior corpus callosum and the thalamic radiations. If there is hand weakness, the examiner may hold and move the object between the patient’s fingers. It is striking to see a patient with a paralyzed hand from a pure motor capsular stroke demonstrate exquisitely intact stereognosis when tested in this fashion. In tactile agnosia, the patient is unable to identify the object with either hand but can identify it visually. Graphesthesia is a similar function. It is tested by writing numbers on the patient’s palm or fingertips. The inability to recognize the numbers is referred to as agraphesthesia; in the presence of intact primary sensory modalities, it usually indicates a lesion involving the contralateral parietal lobe. Cortical sensory functions and abnormalities are discussed further in Chapter 35.

Finger agnosia refers to the loss or impairment of the ability to recognize, name, or select individual fingers of the patient’s own hands or the hands of the examiner. The patient loses the ability to name individual fingers, point to fingers named by the examiner, or move named fingers on request, in the absence of any other naming deficit. Testing for finger agnosia may be conveniently combined with assessment of right-left orientation. The simplest test of right-left orientation is to ask the patient to raise a specific hand. A more challenging test is to have the patient touch a body part on one side (e.g., the right ear) with a specific digit of the other side (e.g., the left thumb). Even more strenuous is when the examiner faces the patient, crosses her forearms with hands and fingers extended, and requests the patient to touch one of the examiner’s fingers on a specific side (e.g., the left index finger). A very challenging test is to ask the patient to touch a specific finger as the examiner faces away from the patient with forearms crossed behind the back. Using a confusing syntax, the examiner might say, “with your left hand, touch my right index finger.”

Finger agnosia and right-left confusion, along with agraphia and acalculia, make up Gerstmann’s syndrome. Finger agnosia alone is not highly localizing, but when all components of the syndrome are present, the lesion is likely to lie in the dominant inferior parietal lobule, particularly in the region of the angular gyrus and subjacent white matter. Current thinking is that pure Gerstmann’s syndrome likely results from a lesion of the subcortical parietal white matter causing disconnection of separate but colocalized fiber tracts disrupting intraparietal cortical networks, rather than a focal cortical lesion.

In the visual agnosias, there is loss or impairment of the ability to recognize things visually, despite intact vision (psychic blindness or mind blindness). Area 18 and area 19 are particularly important for visual gnostic functions. Visual agnosia is not a sensory defect but a problem in recognition. There is impairment in the higher visual association processes necessary for recognition and naming, not explicable by any deficit in visual perception or in naming ability. Patients can see but cannot make sense of the visual world. Teuber said visual agnosia was a “percept stripped of its meaning.” Oliver Sacks provided an entertaining and informative description of the clinical picture of visual agnosia in The Man Who Mistook His Wife for a Hat.

The specifics of which visual functions are preserved or involved vary from patient to patient. Lissauer divided the visual agnosias into apperceptive and associative types. Apperceptive visual agnosia occurs when there is some perceptual defect distorting the visual image so that the object is unrecognizable. It most often follows lesions involving the parietooccipital regions bilaterally and may evolve during recovery from cortical blindness. In apperceptive agnosia, there is lack of recognition because of a visual perceptual impairment above the level of a basic visual function such as acuity, color perception, and visual fields. There is impairment of the more complex perceptions that allow for the synthesis of visual elements. The patient may be able to see parts but not the whole. She may not be able to distinguish a circle from a square or match an object with its picture.

Associative visual agnosia refers to a global inability to identify objects in the absence of visual impairment, aphasia, or anomia. It is a defect in the association of the object with past experience and memory. Patients can readily identify the same objects using other sensory modalities. Associative visual agnosia occurs with bilateral occipitotemporal junction lesions, often involving fusiform gyri. It may also occur when the visual cortex is disconnected from the language centers by a lesion involving the splenium of the corpus callosum and the left occipital lobe, similar to the lesion causing alexia without agraphia. Patients often have related recognition deficits, such as color agnosia and prosopagnosia. The apperceptive-associative scheme has been applied to other types of agnosia as well.

Visual object agnosia (optic aphasia) is an associative visual agnosia causing an inability to recognize things seen that is not because of visual impairment, cognitive deficit, inattention, aphasic misnaming, or unfamiliarity. The patient is unable to identify familiar objects presented visually and cannot correctly identify a seen object from a pick list. She may be able to see the object, even describe it, but have no idea what it is or what it is called. But she recognizes it immediately if allowed to handle it or hear any sound it might make. Visual object agnosia must be distinguished from anomia. The patient with anomia cannot recognize the object when presented by another modality (e.g., touch), and she will have other defects in naming, such as impairment in spontaneous naming with inability to generate word lists (e.g., naming animals). The anomic patient may also be able to demonstrate what the object is by gesture (e.g., appropriately apply a comb to her hair), yet not be able to call it a comb. The patient with agnosia doesn’t recognize the comb as a comb and has no idea what to do with it. Visual object agnosia is often accompanied by right homonymous hemianopia and alexia without agraphia.

Some occipital lobe lesions, particularly of the primary visual cortex, cause color blindness (central achromatopsia). Lesions of the association areas may cause color agnosia. In color agnosia, the patient cannot name or identify colors, although she is not color blind and can discern the numbers on color plates. In prosopagnosia (face or facial agnosia), there is an inability to recognize familiar faces. The patient may not be able to identify people, even close family members, by looking at their faces. However, she may immediately identify the person by the sound of the voice. The patient may recognize a face as a face but cannot associate it with a particular individual. She learns to identify people using other cues. In extreme examples, the patient is unable to recognize herself in a mirror or a photograph. Patients with prosopagnosia, and other visual agnosias, usually have bilateral lesions of the occipitotemporal area involving the lingual, fusiform, and parahippocampal gyri. Prosopagnosia can occur with unilateral right posterior hemispheric lesions. Recent literature suggests that a hereditary form may affect about 2.5% of the population, and perhaps up to 10% in a very mild form. A common complaint is the inability to keep track of characters in movies. Transient prosopagnosia has been reported after focal electrical stimulation of the right inferior occipital gyrus.

Simultagnosia is the ability to perceive only one object at a time or specific details but not a picture in its entirety. The patient may perceive parts but not the whole of a pattern. They may be able to read letter-by-letter but not recognize an entire word. Area 19 is thought to be important in revisualization, and lesions in this region cause a visual agnosia characterized by inability to revisualize, or a loss of visual memory. An object may be identified when seen, but the patient cannot describe it afterward. In the Charcot-Wilbrand syndrome, there is loss of revisualization; the patient cannot draw or construct from memory. Patients may not be able to remember the color of common things (e.g., the sky).

Apraxia (Gr. praxis “action”) is defined in several ways. Common to all definitions is the inability to carry out on request a motor act in the absence of any weakness, sensory loss, or other deficit involving the affected part. The patient must have intact comprehension and be cooperative and attentive to the task. One definition requires the task be high level, learned, familiar, and purposeful, such as saluting or using an implement. But the term is also used to refer to loss of the ability to execute some very elemental functions, such as opening or closing the eyes (eyelid apraxia), glancing to the side (ocular motor or gaze apraxia), walking (gait apraxia), or a behavior as basic as smacking the lips (buccofacial apraxia). Another definition of apraxia is the inability to perform an act on command that the patient is able to perform spontaneously. But the patient with gait apraxia cannot walk spontaneously any better than to command. So, all the definitions and applications of the term suffer in one respect or another. There are many varieties of apraxia. The ones seen most often are ideomotor, buccofacial, constructional, and dressing apraxia. Apraxia of speech is discussed in Chapter 9.

The major limb apraxias are limb kinetic, ideomotor, and ideational. The simplest form is limb kinetic apraxia. This category probably should not exist. These patients have difficulty with fine motor control. They typically have very mild lesions involving the corticospinal tract that are not severe enough to cause detectable weakness, but they are severe enough to impair coordination and dexterity. Limb kinetic apraxia is due to dysfunction of the primary motor pathways. In other forms of apraxia, the primary motor and sensory functions are intact. Pryse-Phillips referred to limb kinetic apraxia as, “an entity of doubtful validity, the clumsiness… probably being due to paresis.”

In ideomotor apraxia, the patient is unable to perform a complex command (e.g., salute, wave goodbye, comb hair, use scissors, flip a coin, show how to hitchhike) with the involved extremity, sometimes with either extremity. The patient may be unable to pantomime how to use common implements (e.g., hammer, toothbrush, comb) or how to kick or throw a ball. She may substitute a hand or finger for the imagined object, thus using a body part as the tool (e.g., raking her fingers through her hair instead of showing how to use a comb or snapping her fingers together as the blades when asked to show how to use scissors). The patient may be unable to carry out the act on command but be able to imitate it. Rarely, the patient may be unable to carry out an act on command or imitation—such as showing how to use a comb—but be able to use the actual object, referred to as dissociation or disconnection apraxia.

In ideomotor apraxia, there may be a disconnection between the language or visual centers that understand the command and the motor areas tasked with carrying it out. Patients may have apraxia for whole body movements. They are unable to, on command, do such things as stand up, take a bow, or stand like a boxer. Lack of apraxia for whole body movements in the presence of apraxia for limb movements has been attributed to sparing of the bundle of Turck, a tract from the posterior superior temporal area to the pontine nuclei (temporopontine tract). As many as 40% of aphasic patients have ideomotor ataxia if correctly tested, but it frequently goes undetected. Depending on the anatomy of the lesion, ideomotor apraxia may affect only contralateral or all four limbs plus midline functions. Some authorities distinguish between parietal and disconnection variants of ideomotor apraxia.

Sympathetic apraxia is the inability of a patient to perform a complex motor act with the nonparetic limb in the presence of a unilateral dominant hemisphere lesion. For instance, a patient with a left hemisphere lesion causing Broca’s aphasia may be unable to show how to wave goodbye using the left hand. This is because the fibers connecting the language areas of the left hemisphere with the motor areas of the right hemisphere are disrupted. The patient understands the request, has no weakness of the left hand, but is unable to execute because the right hemisphere never receives the command.

In ideational apraxia, the patient is able to carry out individual components of a complex motor act, but she cannot perform the entire sequence properly. The patient may perform each step correctly, but in attempting the sequence, she omits steps or gets the steps out of order. There is an inability to correctly sequence a series of acts leading to a goal. Ideational apraxia seems to be an impairment in conceptualizing the overall goal of the activity sequence or an inability to plan the series of steps. For instance, in showing how to drive a car, the patient might try to put the car in drive before starting the engine. When asked to demonstrate how to mail a letter, the patient may seal the envelope before inserting the letter, or mail the letter before affixing the stamp. Ideational apraxia may occur with damage to the left posterior temporoparietal junction or in patients with generalized cognitive impairment. In daily life, patients with ideational apraxia may choose the wrong tool for a task, for example, eat soup with fork, or perform tasks out of sequence, for example, brush teeth before applying toothpaste. In one reported case, a woman trying to light a gas stove first struck the match, then blew it out, then lit the burner. On another occasion, she turned on the gas, filled the kettle, then struck the match, causing a minor explosion.

In buccofacial (oral) apraxia, patients are unable to execute on request complex acts involving the lips, mouth, and face; this may include such activities as whistling, coughing, pursing the lips, sticking out the tongue, blowing a kiss, pretending to blow out a match, or sniffing a flower. There is no weakness of the mouth, lips, or face, but the patients are unable to make the requested movement. The patient may spontaneously lick her lips or stick out her tongue, but she is unable to do so on command. Apraxia of such midline functions is common in patients with lesions involving either hemisphere. Failure to execute such acts should not necessarily be construed as evidence of impaired comprehension in aphasic patients.

Other common types of apraxia include dressing and constructional. Constructional or dressing apraxia usually occurs with parietal lobe lesions, occasionally with frontal lesions that interfere with the patient’s ability to comprehend spatial relationships. In constructional apraxia, the patient is unable to copy geometric forms of any complexity because of impaired visuospatial skills. She may be able to draw a square but not a three-dimensional cube. She may be able to draw individual shapes, but she cannot synthesize them into a more complex geometric figure (e.g., a square with a triangle perched on its upper-right corner and a circle attached to the lower-right corner, all touching). The patient may also be asked to draw actual things, such as a three-dimensional house with a roof and chimney, a clock, or a daisy.

Patients with hemineglect may fail to put petals on one side of the daisy. A test for both praxis and cognition is to have the patient draw a clock face, insert the numbers, and draw the hands at a specific time (e.g.:10, or “10 minutes past 3”). Patients with hemineglect may fail to put the numbers on one side of the clock. Patients with frontal lobe dysfunction or a confusional state may have a disorganized and confused approach to the task, making multiple errors. A patient with cognitive impairment may forget the proper arrangement of numbers or how to indicate a specific time. Some patients cannot interpret 3:10 and will put one hand on the 10 and the other on the 3, indicating 2:50 or 10:15. The clock drawing test is discussed further in Chapter 8. The Rey-Osterrieth figure is very complex and can bring out subtle constructional apraxia (Figure 10.1). Constructional tasks are particularly useful for differentiating psychiatric from neurologic disease. Impaired constructional ability is a sensitive indicator of lesions involving various parts of the brain, but in patients with psychiatric disease, constructional ability is preserved.

FIGURE 10.1 The Rey-Osterrieth complex figure for evaluating constructional ability.

In dressing apraxia, the patient loses the ability to don clothing correctly. Dressing requires bimanual cooperation to solve a complex spatial problem. There is loss of the ability to manipulate the clothing in space and to understand its three-dimensional relationships. Patients with hemineglect may fail to dress one side of the body. A useful test for dressing apraxia is to turn one sleeve of the hospital gown or robe inside out and then ask the patient to put it on. Patients with dressing apraxia are often baffled. Dressing apraxia can be particularly disabling, as the patient struggles for a long period of time each morning simply to get dressed. Constructional apraxia would be very disabling for a patient who was an artist or craftsman. Dressing apraxia often occurs in conjunction with constructional apraxia.

Disconnection Syndromes

Disconnection syndromes are disorders in which the fiber tracts that interconnect primary cortical areas are disrupted, with preservation of the cortical areas of origin. Neurologic dysfunction occurs not because of destruction of cortex but because of defects in intrahemispheric or interhemispheric communication. In 1874, Wernicke was the first to suggest that such a pathoanatomic mechanism might exist when he described conduction aphasia in his MD thesis, written at the age of 26. Dejerine added alexia without agraphia in 1892. In his 1965 paper, Disconnection syndromes in animals and man, which became the manifesto of behavioral neurology, Geschwind expanded and popularized the concept, describing several new examples. Other disconnection syndromes include ideomotor apraxia, sympathetic apraxia, pure word deafness, and the transcortical aphasias. The modality-specific agnosias may be disconnection syndromes in which the primary sensory area for a given modality is disconnected from the language and memory areas of the brain that are responsible for recognition and naming. Disconnection syndromes may result from any process that disrupts subcortical white matter, including infarction, hemorrhage, neoplasm, and trauma. There have been reports of patients with double disconnection syndromes.

In alexia without agraphia, a left occipital lobe lesion, usually an infarction, extends anteriorly to involve the splenium of the corpus callosum or the adjacent white matter. Patients usually have a right homonymous hemianopia because of the occipital lobe lesion. Although the right occipital lobe and left visual field are intact, fibers from the right occipital lobe are disconnected from the language centers in the left parietal lobe because of disruption of commissural fibers in the splenium. The patients are unable to read because the visual information from the right occipital lobe cannot be transferred to the region of the opposite angular gyrus. They are typically better able to read letters than words, and individual letters better than letter strings. Preservation of number reading may occur. Because the angular gyrus is itself intact, patients are able to write without difficulty but are unable to read what they may have just written. Rarely, alexia without agraphia occurs without an accompanying hemianopia.

In pure word deafness (auditory verbal agnosia), patients are unable to understand speech, but other language modalities are unimpaired. Spontaneous speech, reading, and writing are preserved in the face of a severe auditory comprehension deficit. Hearing is intact, and nonlanguage auditory processing (e.g., for music) is undisturbed. Responsible pathology is typically bitemporal or dominant temporal, causing disconnection of Wernicke’s area from the primary auditory cortex. In pure word blindness, the patient cannot read, but other language functions are intact. The lesion disconnects the visual cortex from the language centers. There is conjecture that the dysphagia in Wallenberg’s lateral medullary syndrome may be due to a disconnection between premotor neurons related to swallowing and the bulbar nuclei responsible for execution.

In callosal disconnection syndromes, there is evidence of interhemispheric disconnection causing deficits in corpus callosum function that resemble those seen in split-brain patients. Patients with anterior callosal lesions may have unilateral tactile anomia, unilateral agraphia, unilateral apraxia, difficulty in copying drawings, dyscalculia, abnormalities of somesthetic transfer, and the alien hand phenomenon. Posterior callosal lesions may cause left tactile anomia, left visual anomia, and agraphia of the left hand. A patient with infarction of the total length of the corpus callosum had unilateral verbal anosmia, hemialexia, unilateral ideomotor apraxia, unilateral agraphia, unilateral tactile anomia, unilateral constructional apraxia, lack of somesthetic transfer, and dissociative phenomena. Callosal apraxia refers to impaired ability to pantomime to command, imitate, or use actual objects with the left hand, with spared ability to perform these tasks with the right hand, because of a callosal lesion. Evidence of callosal disconnection has been reported in infarction, hemorrhage, Marchiafava-Bignami disease, multiple sclerosis, and Alzheimer’s disease.

Attentional Deficits

In addition to the generalized defects in attention seen in patients with altered mental status and other diffuse cerebral disturbances, there may be selective defects of attention in patients with focal cerebral lesions. These are seen primarily in right-handed patients with right (nondominant) hemisphere lesions, especially those that involve the inferior parietal lobule. A variety of terms has been used to describe the phenomenon, including extinction, neglect, hemineglect, hemi-inattention, denial, and spatial inattention. Hemiattention may be modality specific. The mildest manifestation of a right parietal lesion is extinction of the contralateral stimulus with double simultaneous stimulation on visual field or somatosensory testing. Although primary sensory modalities are intact, when touched simultaneously on both sides, the patient fails to appreciate the stimulus on the involved side or fails to see the stimulus in the involved visual hemifield.

Patients with multimodal hemineglect may extinguish all types of contralesional stimuli, and they may completely ignore the left side of space. On the line bisection test, they fail to see the left half of the line (Chapter 8). They bisect the right half, drawing their vertical tick about one-quarter of the way down the line from the right. If lines are drawn all over the page, patients may fail to bisect any of the lines on the left. When presented with a complex drawing, such as the cookie theft picture, they may describe what is taking place on the right side of the picture, but they may fail to notice the cookie theft happening on the left. It appears that the right parietal lobe is dominant for spatial attention; subtle ipsilateral deficits may also occur. In addition, the left hemisphere plays a role in attention to contralateral stimuli only. With a right-sided lesion, the left hemisphere still adequately attends to the right side of space, and the deficit appears in contralateral hemispace left unguarded by the right hemisphere. In motor neglect (hemiakinesia), all of the patient’s motor activities are directed to one side of space.

Babinski introduced the cumbersome term anosognosia to refer to a patient’s lack of awareness of a neurologic deficit. It occurs particularly in patients with nondominant parietal lesions. It has been estimated at seven times more common with nondominant than dominant lesions, a difference not wholly explicable by associated aphasia with dominant lesions. It is not uncommon to see patients with a right parietal infarction on imaging studies but no clinical history of the event, in part because of this lack of recognition of deficits involving the left side of the body. Occasionally, a patient with severe left hemiplegia may deny there is anything wrong with the involved limbs. Even when the examiner dangles the patient’s paralyzed left hand before her face and asks if there is anything wrong with this hand, the patient may deny it. The most severe form of anosognosia is when the patient denies owning the hand (asomatognosia). Occasionally, patients become belligerent in denying that the hand dangling before them is theirs. They commonly say the hand belongs to the examiner. One patient stated it was, “Queen Elizabeth’s hand.” When asked where Queen Elizabeth was, the patient replied, “behind the curtain.” Patients with anosognosia may refuse to remain in the bed with this “other person.” One patient thought her left arm was her grandbaby lying beside her. One patient, convinced her left arm was not her own, threw it over the side rail of the bed, fracturing the humerus (see section on “Alien Hand Syndrome”). In misoplegia, also seen with right hemisphere lesions, patients hate and may reject their paralyzed limbs. A possibly related disorder, also attributed to a right parietal lesion, is apotemnophilia, in which otherwise apparently rational individuals seek amputation of healthy limbs.

Patients with persistent anosognosia typically have large right hemisphere strokes causing severe left hemisensory loss and left spatial neglect. Anosognosia for the hemiplegia may result from impaired proprioceptive mechanisms that leave the patient unaware of the position and movement of the affected limbs. Anosognosia for hemiplegia has also been reported with pontine lesions. Using special techniques to compensate for aphasia, it may be detected more often in dominant hemisphere lesions than previously suspected. Patients may deny or neglect other neurologic deficits as well, particularly loss of vision due to bilateral occipital lobe lesions (cortical blindness, Anton’s syndrome).

Alien Hand Syndrome

In alien hand syndrome, there is complex but involuntary activity in one hand; the hand moves as if it had a mind of its own. There is debate about whether the activity need appear purposeful and goal directed. Alien hand syndrome is usually due to interruption of the cortical connections that control smooth bimanual operations. The hands no longer work as a team. The affected hand begins to function autonomously and loses the ability to cooperate with its fellow. The patient feels a loss of ownership of the extremity. There may be outright intermanual conflict. The affected hand acts as if possessed by a poltergeist. If the patient tries to eat with the good hand, the alien hand may grasp the good hand and force it away from the mouth. If the good hand tries to write, the alien hand may snatch the pen.

There are at least two forms of alien hand syndrome. In the callosal form, there is a lesion in the anterior corpus callosum. Intermanual conflict is typical of the callosal form, and it nearly always affects the left hand (anarchic hand). In the frontal form, there is a lesion of the medial frontal lobe, near or involving the supplementary motor area. The alien hand is uncooperative but not contentious. It may display reflex grasping and other autonomous behavior, but there is little or no intermanual conflict. Patients may complain of the hand’s behavior and may criticize it or even slap the alien hand with the good hand. Other patients regard the hand’s behavior as amusing.

A sensory or posterior alien hand syndrome has also been described following parietal lobe lesions. There are typically parietal sensory deficits and hemineglect involving the left side of the body, which resemble anosognosia. The left arm may then involuntarily attack the right side of the body. There have been reports of patients with a callosal lesion feeling as though they had a second left hand.

Other neurologic examination abnormalities help indicate the alien hand subtype. Nonfluent aphasia and a prominent grasp reflex suggest the frontal lobe variant. Ideomotor apraxia of the nondominant hand suggests the callosal form. A hemisensory deficit and other parietal lobe findings suggest the sensory alien hand variant. Potential etiologies include stroke, corpus callosotomy, hypoglycemic encephalopathy, diabetic hypermolar syndrome, Marchiafava-Bignami disease, MS, migraine, and posterior reversible encephalopathy syndrome. Alien hand syndrome occurs in degenerative cerebral disorders, including corticobasal syndrome, Alzheimer’s disease, and Creutzfeldt-Jakob disease. The incidence of alien hand in corticobasal syndrome has been reported as high as 40% to 50%, making corticobasal syndrome potentially the commonest etiology for alien hand syndrome.

The alien hand syndrome has appeared many times in pop culture. In Dr. Strangelove, Peter Sellers constantly has to restrain his alien hand from giving the Nazi party salute and alien hand syndrome has been referred to as Dr. Strangelove syndrome.

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