Nitrous oxide induced myeloneuropathy
History of tingling sensation in all extremities and burning sensation in bilateral soles; weakness and difficulty walking for 1 week. Physical exam reveals decreased light touch and pinprick sensation in all extremities with distal to proximal gradient. Decreased vibration sense in both feet. Hyporeflexia in upper limbs and absent reflexes in both lower limbs. Rhomberg sign weakly positive. No bladder or bowel incontinence.
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Patchy increased signal intensity from C1-C5 affecting dorsal column. Axial T2 mid-cervical demonstrates bilateral hyperintensity in the dorsal column (inverted V sign). No cord compression or edema seen.
Further investigations revealed:
- Vitamin B12 : 279pg/mL
- Homocysteine : 58 nmol/mL
- MMA :1.59 nmol/mL
Further social history reveals nitrous oxide abuse, she used about 5-10 canisters of nitrous oxide per week. She is negative for HIV and other investigations were unremarkable.
A clinical diagnosis of myelopathy due to nitrous oxide toxicity was made.