Testing for apraxia is carried out in several ways. First, one observes the actions of the patient as he engages in simulated tasks as dressing, washing, shaving, and using eating utensils. Second, the patient is asked to carry out familiar symbolic acts—wave goodbye, salute the flag, shake a fist as though angry, or blow a kiss. If he fails, he is asked to imitate such acts made by the examiner. Finally, he is asked to show how he would hammer a nail, brush his teeth, take a comb out of his pocket and comb his hair, or to execute a more complex act, such as lighting and smoking a cigarette or opening a bottle of soda, pouring some into a glass, and drinking it. These latter actions, involving more complex sequences, are said to be tests of ideational apraxia; the simpler and familiar acts are considered tests of ideomotor apraxia. To perform these tasks in the absence of the tool or utensil is always more demanding because the patient must mentally formulate a plan of action rather than engage in a habitual motor sequence. The patient may fail to carry out a commanded or suggested activity (e.g., to take a pen out of his pocket), yet a few minutes later he may perform the same motor sequence automatically.
Children with various cerebral diseases that delay development are often unable to learn the sequences of movement required in hopping, jumping over a barrier, hitting or kicking a ball, or dancing. They suffer a developmental motor apraxia. This leads to a form of physical awkwardness that may be seen in the developmentally delayed child. Certain tests quantitate failure in these age-linked motor skills (see Chap. 27).
In the authors’ opinion, the time-honored division of apraxia into ideational, ideomotor, and kinetic types is not entirely satisfactory because of the difficulty separating them in practice. We have sometimes been unable to confidently separate ideomotor from ideational apraxia. The patient with a severe ideomotor apraxia nearly always has difficulty at the ideational level and, in any case, similarly situated left parietal lesions give rise to both types. Furthermore, in view of the complexity of the motor system, we have frequently been uncertain whether the clumsiness or ineptitude of a hand in performing a motor skill represents a kinetic apraxia or some other subtle fault in hand control by the corticospinal or one of the other parallel motor systems.
A related but poorly understood disorder of movement has been termed the alien hand. In the absence of volition, the hand and arm undertake complex and seemingly purposeful movements such as reaching into a pocket or handbag, placing the hand behind the head, tugging on the opposite hand or other body part, and rebuttoning the shirt immediately after it has been unbuttoned by the other hand. These activities may occur even during sleep. The patient is aware of the movements but has the sense that the actions are beyond his control and there is often an impression that the hand is estranged, as if commanded by an external agent (although the limb is recognized as one’s own—there is no anosognosia); a grasp reflex and a tendency to grope are usually present. Most instances arise as a result of infarction in the territory of the opposite anterior cerebral artery, including the corpus callosum. When the callosum is involved, Feinberg and colleagues find that there frequently appears to be a conflict between the actions of the hands, the normal one sometimes even restraining the alien one. Damage in the left supplementary motor area from any cause, as well as from the degenerative parietal lobe disease called corticobasal ganglionic degeneration are associated with a similar alien hand syndrome. A third form that results from a stroke in the posterior cerebral artery territory with associated sensory loss has also been observed by Ay and colleagues.