Subacute ascending numbness

A 21-year-old male presented with two weeks of ascending numbness involving all 4 limbs, and imbalance when walking. Examination revealed diminished vibration and proprioception at the fingers, toes, and ankles, a high steppage gait and a positive Romberg sign. He had no weakness in any muscle groups. Laboratory data included vitamin B12 218 pg/mL (normal range: 200-800 pg/mL), homocysteine 87 μmol/L (normal range: 2.2-13.2 μmol/L), and non-reactive RPR. Magnetic resonance imaging of the cervical spine revealed abnormal T2-weighted hyperintensity along the posterior columns extending from C2 to C7.