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A neurologic examination of a 58-year-old man reveals a spastic paralysis in the left leg, very brisk knee jerk and ankle reflex on the left side, and an extensor left plantar response. Which is the most likely site of the lesion?
A. Left lumbar enlargement of the spinal cord
B. Left medial superior precentral gyrus
C. Right inferior medulla
D. Right inferior precentral gyrus
E. Right midbrain
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DD?? Right inferior precentral gyrus
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Option A (Left lumbar enlargement of the spinal cord) is correct. A lesion of the corticospinal tract in the spinal cord causes an upper motor syndrome ipsilateral below the site of the lesion.
Option B (Left medial superior precentral gyrus) is incorrect. This lesion in the medial aspect of the superior precentral gyrus causes a spastic paralysis of the right leg.
Option C (Right inferior medulla) is incorrect. A lesion in this area impairs the corticospinal tract and causes spastic paralysis on the contralateral side. The patient would also suffer from other severe symptoms, and the arm would be affected too.
Option D (Right inferior precentral gyrus) is incorrect. A lesion in this region would cause paralysis of the left face and arm.
Option E (Right midbrain) is incorrect. A lesion in this area would cause spastic paralysis on the left side, but the patient would also suffer from other severe symptoms, and the arm would be affected too.
