USMLE Answer 45

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45. The correct answer is A. The patient has tabes dorsalis, which is a form of neurosyphilis seen 10 to 25 years or longer after primary disease. The pupils described are Argyll Robertson pupils and are considered diagnostic for neurosyphilis. Characteristically, the dorsal columns, which contain the ascending tracts for sensory information, become atrophic, probably as a result of damage to the dorsal root ganglion cells.

The dorsal gray horn (choice B) contains neurons that respond to sensory input.

The lateral column (choice C) contains both descending (e.g., lateral corticospinal, rubrospinal tracts) and ascending (e.g., spinocerebellar tracts, spinothalamic tracts) tracts.

The ventral column (choice D) contains both descending (e.g., anterior corticospinal, tectospinal) and ascending (e.g., spinothalamic) tracts.

The ventral horn (choice E) contains lower motor neurons.