What Is the Cause of This Young Person’s Paresthesias and Weakness?

A 30-year-old male presents to clinic complaining of bilateral lower extremity weakness which has been getting slowly worse over the past 8 years. He endorses decreased sensation with mild burning paresthesias in his legs for many years, and more recently noticed tingling in his hands as well. He does not smoke or use recreational drugs, but does have a glass of wine with dinner most nights. His mom and brother also have high arches, and his mom recently started using a wheelchair due to frequent falls. He has no other significant medical history, and avoided doctors until recently when he felt the weakness began to interfere with his day-to-day life.

On exam, he has moderate symmetric weakness of plantar and dorsiflexion, and mild weakness of knee flexion and extension. Finger and arm strength are intact. He has decreased sensation to pinprick and vibration in the upper extremities in all fingers to the midpalm, and in the lower extremities from the toes to just above the knee, combined with the mild burning paresthesias noted earlier. Romberg test is positive. Biceps and brachioradialis reflexes are mildly decreased in both arms, while patellar and achilles reflexes are absent in his lower extremities. His gait is hesitant with bilateral foot drop.

His primary care provider has checked HbA1c, folate, B12, serum protein immunofixation (SPEP), erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), and thyroid stimulating hormone (TSH) which were unremarkable.

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