470 - Rehabilitation for Nitrous Oxide Induced Subacute Combined Degeneration

Case Diagnosis: Subacute Combined Degeneration of the Spinal Cord

Case Description: A 37-year-old, previously independent man, presented to the emergency department with one week of cramping, paresthesia, and worsening balance. Review of systems was positive for paresthesia and hypoesthesia that began in the lower extremities (LE) (L > R). Approximately 3 days later he began to experience hypoesthesia and paresthesia in his upper extremities (UE). Social history was positive for alcohol, marijuana, and whippet (nitric oxide) use. He reports walking 20 blocks daily prior to admission, however on presentation was unable to ambulate. Pertinent negatives included bowel incontinence, saddle anesthesia, and fever. Physical examination was notable for global ataxia, decreased light touch sensation, LE joint position sense deficits, increased LE adductor tone, and clonus in the LE despite normal strength. Laboratory results were positive for elevated homocysteine (Hcy). MRI revealed hyperintensity of the dorsal column of the cervical spinal cord.

Discussions: Nitric Oxide (whippets) interferes with vitamin B12 metabolism and inhibits methionine synthase which can lead to development of subacute combined degeneration (SCD). Vitamin B12 is a coenzyme used in the synthesis of methionine from Hcy which is integral for neuronal sheath integrity. MRI findings and elevated Hcy were consistent with SCD. Management is focused on both B12 supplementation as well as interdisciplinary rehabilitation to address balance, truncal control, proprioceptive re-education, and functional independence. LE spasticity was a late finding in the presentation which was managed with oral Baclofen. The patient was successfully able to transition home after four weeks in the acute rehab setting.

Conclusions: Nitric oxide misuse is an important risk factor to elucidate for patients with signs and symptoms of SCD. Spasticity may also be a notable finding despite preserved strength. Early rehabilitation interventions are integral to functional recovery in this disease course.