Motor Functioning

The following are features of motor impairment in AD:

Pyramidal signs Hyperreflexia Plantar responses Extrapyramidal signs Tremor Rigidity Bradykinesia Gait disturbances Primitive reflexes Apraxia Ideational Ideomotor

Not all people with AD exhibit the full spectrum of deficits. A general feature of AD is that the primary motor cortex is relatively preserved. However, pyr amidal signs may be seen in AD; these include hyperreflexia, extensor plantar responses, hyperactive jaw jerk reflex, and ankle clonus. The mechanism for this is unclear but may involve either diffuse white matter or associated vascular dementia. Extrapyramidal signs exist, and the most common are bradykinesia (slowness of movement) and rigidity (increased resistance to passive movement). Tremor is infrequent. Gait abnormalities consist of slowness in walking, with decreased step length, paucity arm swing, and a droop posture, all of which may become more apparent as the dementia progresses. Myoclonus can occur early on, but motor seizures are regarded as happening later. Primitive reflexes of two types, nocioceptive and prehensile, are also seen in AD. The nocioceptive type, which includes the snout reflex, the glabellar blink reflex, and the palmomental reflex, occurs in approximately 20-50% of cases and can be seen early on. Of these, the snout and palmomental reflexes are the most common. The prehensile type, which includes grasping, sucking, and rooting, is less frequent (1020% of cases) and is associated with late-stage dementia.

The two common types of apraxia are seen in AD, according to the strict definition of this term. Idea-tional apraxia, which involves impairment of the ability to perform actions appropriate to real objects, is frequently observed in AD, as is ideomotor apraxia. The latter refers to selection of elements that constitute movement, such as in copying gestures and miming usage. It has been estimated that the presence of both ideational and ideomotor apraxia occurs in 35% of patients with mild, 58% with moderate, and 98% with severe AD. Tool action knowledge has also been characterized as conceptual apraxia and found to be dissociable in AD from semantic language impairment.

In the moderate or severe range, another motor feature that can be observed is motor impersistence. This is an impairment in the ability to sustain a voluntary movement (e.g., exerting a steady hand grip or keeping the eyes closed). This is distinguished from apraxia because the movement can be performed and maintained with instruction. This type of motor impairment is strongly related to frontal lobe involvement.

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