Subacute Combined Degeneration as a Red Herring for Acute Traumatic Spinal Cord Injury

Subacute combined degeneration (SCD) is a potentially reversible neurologic disorder caused by vitamin B12 deficiency that classically affects the dorsal columns of the spinal cord. Clinical manifestations include sensory loss, gait instability, weakness, and, less commonly, autonomic dysfunction. With these neurologic manifestations, patients may present with recurrent falls, and SCD can mimic the presentation of acute traumatic spinal cord injury (SCI). In this case, a 66-year-old man with a recent history of nitrous oxide use presented with bilateral lower extremity weakness, sensory changes, and gait instability, resulting in recurrent ground-level falls. Initial evaluation for traumatic SCI was unrevealing, and the patient was discharged home. Due to continued symptom progression, the patient presented again and underwent further workup that demonstrated significant B12 deficiency secondary to pernicious anemia. Cervical MRI revealed symmetric dorsal column T2 hyperintensity in the axial plane forming the "inverted V" sign that is characteristic of SCD. Despite serum B12 level correction, the patient had persistent neurologic deficits requiring admission to inpatient rehabilitation. This case highlights SCD as an important diagnostic consideration in the setting of acute trauma and emphasizes the importance of patient risk factors such as nitrous oxide abuse. Accurate diagnosis is contingent on recognition of key imaging findings and pursuit of further laboratory workup, especially when initial traumatic workup is negative. Early diagnosis is critical as delayed treatment may result in irreversible neurologic impairment and functional disability.