Lhermitte's Phenomenon as the Presenting Symptom of Vitamin B12 Deficiency With Complete Reversibility of Neurological and Radiological Abnormalities.

Vitamin B12 deficiency is a potentially reversible cause of neurological dysfunction, including myelopathy. We present a case of a 37-year-old man with Lhermitte's sign and distal paresthesia but without focal neurological deficits. Laboratory evaluation showed low-normal serum B12 with elevated intrinsic factor antibodies. MRI revealed cervical spinal cord hyperintensity involving the posterior columns (C2 to C5), which fully resolved following vitamin B12 supplementation. This case underscores that neurological manifestations of B12 deficiency may occur even with "normal" B12 levels and no hematologic abnormalities and highlights the importance of early recognition and treatment to reverse both clinical and radiologic findings.