Nitrous oxide-induced predominantly motor neuropathies: a follow-up study

Objectives Recreational nitrous oxide (N 2 O) abuse is increasingly popular among youth. We report a systematic clinical, electrophysiological and biological follow-up of patients with neuropathy caused by N 2 O. Methods We retrospectively report seven patients with neuropathy attributed to N 2 O abuse and their comprehensive follow-up. Demographic, toxicological, clinical, biological and electrophysiological data were collected at first and second examination. Functional data were collected at the last evaluation. Results Seven patients aged 18–30, consuming more than 140 gas-filled balloons (one balloon is filled with approximately 8 g of N 2 O) per week for over a month, developed a severe, predominantly motor, length-dependent, progressive neuropathy over 3 to 6 weeks. Two-thirds presented associated signs of myelopathy. Distal lower limbs motor deficit and ataxia led to moderate disability. Spinal cord imaging was frequently normal. Nerve conduction studies disclosed an almost exclusively motor axonal neuropathy affecting the lower limbs with active denervation. Homocysteine plasma level was systematically elevated, whereas cobalamin plasma levels were normal in almost all patients. At short-term follow-up after intoxication discontinuation, ataxia and motor deficit only partially resolved despite vitamin B12 supplementation, while active denervation and homocysteinemia decreased. At last follow-up (median 9.2 months, IQR 7.5–10.75), mean ONLS was 2.0 (IQR 2.0–2.0). Discussion Young patients, with induced N 2 O motor neuropathy remain disabled after 5 to 14.5 months of gas withdrawal, despite vitamin B12 supplementation. A longer follow-up is needed to fully appraise the severity of these toxic neuropathies.