Clinical Reasoning: A 68-Year-Old Man With Progressive Numbness, Vertigo, and Cognitive Decline.

A 68-year-old man presented with subacute progressive numbness in his lower extremities and vertigo. Concurrently, he developed behavioral and cognitive changes. Initial examination demonstrated mild distal symmetric weakness in the lower extremities, allodynia in the feet, decreased proprioception at the ankles, and absent reflexes in the lower extremities. Electrodiagnostic studies showed a length-dependent, severe axonal sensorimotor polyneuropathy. He was hospitalized after experiencing daily falls and worsening executive dysfunction, during which time additional cognitive history and examination were completed. MRI brain revealed diffusion restriction in the bilateral caudate nuclei. Ultimately, CSF testing solidified the clinical diagnosis. This case highlights the differential diagnosis and diagnostic approach for rapidly progressive neuropathies associated with cognitive decline.