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ANATOMICAL AND FUNCTIONAL PROPERTIES OF NEURONS AND MUSCLE

A 48-year-old man complains of pronounced shaking (4-8 Hz) of both his left and right hands and arms as well as his head. The patient reports that the tremor of the hands and head subsides during walking, after taking an alcoholic drink, and after treatment with the β-adrenergic antagonist propranolol, but it gets exaggerated during states of anxiety. Which of the following is the most likely diagnosis?

a. Parkinson disease

b. Essential tremor

c. Dystonia

d. Cerebellar ataxia

e. Huntington disease

The answer is B. (Aminoff, pp 243-245. Ropper, pp 89-94.) Essential tremor is characterized by a relatively low frequency of 4 to 8 Hz. It involves both arms and may extend to the head. The tremor is reduced by movement such as walking, with intake of alcohol, and following treatment with a β-adrenergic antagonist (eg, propranolol); it is exaggerated during states of anxiety. In Parkinson disease, the face and lips are preferentially affected and the tremor is typically not symmetrical. In Huntington disease, chorea and dementia are prominent characteristics. Cerebellar ataxia (sometimes called intention tremor) occurs during an act of movement, when fine adjustments of the movement are required. Dystonia refers to persistent posture of the extremes of athetoid movement, in which the axial muscles are typically involved and the limb is placed in an unnatural position; further, there may be retroflexion of the head or torsion of the spine.

A 68-year-old woman is examined by a neurologist after she experiences difficulties in walking. When the tendon in the right arm is passively stretched, it results in repetitive, involuntary, and rhythmic contractions of the muscles of that limb at an approximate rate of 5 to 7 Hz. The neurologist concludes that she had a lesion in which of the following areas?

a. Cerebral cortex

b. Gray matter of spinal cord

c. Peripheral nerve in the right arm

d. Vermis of the flocculonodular lobe

e. Dorsomedial pontine tegmentum

The answer is A. (Ropper, pp 46-53, 96-98. Siegel and Sapru, pp 336-337.) Repetitive, rhythmic, involuntary contractions at a rate of approximately 5 to 7 Hz that occur following passive stretch of the tendon describe the pathological reflex of clonus. Clonus occurs as part of a hyperreflexic state that is characteristic of spasticity in an upper motor neuron disorder. Lesions of motor regions of the cerebral cortex result in a hyperreflexic state. Lesions of the vermal ...

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