A 27-year-old man presents with weakness and absent reflexes after a viral infection. What is the most likely cause of his symptoms?

• A. Anterior horn cell degeneration
• B. Axonal polyneuropathy
• C. Demyelinating polyneuropathy
• D. Conversion disorder

Answer: (C)

The symptoms described, particularly weakness and absent reflexes following a viral infection, are most consistent with a demyelinating polyneuropathy, commonly known as Guillain-Barré syndrome (GBS). This syndrome often follows an illness, especially viral infections, and leads to the immune system mistakenly attacking the peripheral nerves, resulting in demyelination. The demyelination disrupts the normal conduction of electrical impulses along the nerves, which explains both the weakness and the absent reflexes.

In Guillain-Barré syndrome, the progression typically starts in the lower extremities and can ascend to involve further muscle groups, often leading to significant weakness. The demyelination observed in GBS is characterized by inflammation and damage to myelin sheaths, which is distinctly seen in the context presented. Thus, the combination of recent viral infection and the specific symptoms makes demyelinating polyneuropathy the most likely cause of the man's condition.