In Crohn's disease involving the terminal ileum, vitamin B12 deficiency commonly presents with which neurological symptom?

• A. Seizures
• B. Peripheral neuropathy
• C. Optic neuropathy
• D. Myopathy

Answer: (B)

When Crohn disease affects the terminal ileum, absorption of vitamin B12 is impaired. B12 is essential for myelin maintenance in nerves, so a deficiency leads to neurologic demyelination. The classic neuro manifestation in this setting is peripheral neuropathy, presenting as numbness, tingling, and sometimes weakness in the legs, which can progress to gait disturbance.

Other neurologic features can occur with B12 deficiency (such as dorsal column–related problems like impaired vibration and position sense), but the most characteristic and commonly tested symptom in this context is peripheral neuropathy. Seizures and optic neuropathy are not the typical presentation here, and myopathy is not a hallmark of B12 deficiency.