Subacute combined degeneration (SCD) is a neurological complication of Vitamin B12 deficiency characterized by demyelination and degeneration of the dorsal and lateral columns. There is no gold standard test for diagnosing B12 deficiency as the presentation can be non-specific and the levels of current markers can vary between patients. 

A 35-year-old male with a history of heavy alcohol use presented with two weeks of progressive ascending numbness and tingling, affecting his gait.  

Neurological examination revealed decreased sensation in the lower extremities progressing upwards. Motor exam significant for bilateral proximal lower extremity weakness. Reflexes were diminished in the upper extremities and absent in the lower extremities. Laboratory tests showed macrocytic anemia. MRI spine imaging showed multifocal cord signal abnormality in the cervical and thoracic cord, mainly in the posterior columns, consistent with SCD. Lumbar puncture performed for Guillain Barre Syndrome (GBS) concern showed no albuminocytologic dissociation. The patient was diagnosed with SCD secondary to B12 deficiency. The patient was started on aggressive intramuscular Vitamin B12 supplementation (1000mcg every other day) for the remainder of hospital admission. His symptoms improved significantly within 5 days, with near-complete recovery of sensations before discharge. The patient was discharged with a rolling walker and outpatient physical therapy. B12 supplementation was transitioned to 1000mcg oral daily.