A 36-year-old woman is evaluated in the clinic due to left hand clumsiness. The patient works as
an office secretary and has been having difficulty typing. Six months ago, she had an episode of
vertigo and difficulty walking that improved after several weeks. The patient also has a history of
bipolar disorder and takes valproic acid. On physical examination, she is asked to close her eyes
and stretch out her arms with the palms facing up Several seconds later, her left arm
involuntarily drifts downward and the palm turns toward the floor. Which of the following best
explains the findings observed in this patient?
e’) A Basal ganglia dysfunction
e> B. Cerebellar dysfunction
e’) C. Drug-induced hyperammonemia
e> D. Impaired proprioception
e’) E. Pyramidal tract lesion
This young woman with neurologic deficits disseminated in space and time (eg, hand clumsiness,
ataxia, vertigo) most likely has multiple sclerosis, an inflammatory demyelinating disorder
characterized by white matter lesions in the central nervous system
Pronator drift is a physical examination finding that is relatively sensitive and specific for upper
motor neuron or pyramidal/corticospinal tract disease. The pronator drift test is particularly
useful in patients with subtle deficits as it can accentuate pyramidal motor weakness. It is
performed by having the patient outstretch the arms with the palms up and eyes closed (so
that only proprioception is used to maintain arm position) Upper motor neuron lesions cause
more weakness in the supinator muscles compared to the pronator muscles of the upper limb. As
a result, the affected arm drifts downward and the palm turns (pronates) toward the floor.
(Choice A) Basal ganglia dysfunction typically results in extrapyramidal signs, such as resting
tremor, rigidity, bradykinesia, and choreiform movements. Pronator drift is not typically observed.
(Choice B) Cerebellar dysfunction usually causes ataxia, intention tremor, and impaired rapid
alternating movements. Pyramidal tract signs, such as pronator drift, focal weakness, spasticity,
hyperreflexia, and Babinski sign, are not observed with cerebellar lesions.
{Choice C) Drug-induced hyperammonemia can be observed in patients using valproic acid and
usually presents with encephalopathy (eg, confusion, lethargy) and neuromuscular findings (eg,
bradykinesia, asterixis) Focal weakness and pronator drift are not characteristic.
(Choice D) Proprioception is evaluated by passively moving the distal phalange of a digit up and
down and having patients identify the direction of movement with their eyes closed. It is also
assessed with the Romberg test in which patients are observed for unsteadiness as they stand
with their feet together, arms to the sides, and eyes closed. Patients with impaired proprioception
(eg, vitamin B, deficiency, tabes dorsalis) have difficulty determining joint position and may lose
balance during Romberg testing.
Educational objective:
a result, the affected arm drifts downward and the palm turns (pronates) toward the floor.
(Choice A) Basal ganglia dysfunction typically results in extrapyramidal signs, such as resting
tremor, rigidity, bradykinesia, and choreiform movements. Pronator drift is not typically observed.
(Choice B) Cerebellar dysfunction usually causes ataxia, intention tremor, and impaired rapid
alternating movements. Pyramidal tract signs, such as pronator drift, focal weakness, spasticity,
hyperreflexia, and Babinski sign, are not observed with cerebellar lesions.
(Choice C) Drug-induced hyperammonemia can be observed in patients using valproic acid and
usually presents with encephalopathy (eg, confusion, lethargy) and neuromuscular findings (eg,
bradykinesia, asterixis). Focal weakness and pronator drift are not characteristic.
(Choice D) Proprioception is evaluated by passively moving the distal phalange of a digit up and
down and having patients identify the direction of movement with their eyes closed. It is also
assessed with the Romberg test in which patients are observed for unsteadiness as they stand
with their feet together, arms to the sides, and eyes closed. Patients with impaired proprioception
(eg, vitamin B, deficiency, tabes dorsalis) have difficulty determining joint position and may lose
balance during Romberg testing
Educational objective:
Pronator drift is a relatively sensitive and specific sign for upper motor neuron or pyramidal tract
disease affecting the upper extremities. It is performed by having the patient outstretch the arms
with the palms up and eyes closed. In patients with pyramidal lesions, the affected arm drifts
downward and the palm turns (pronates) toward the floor.