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

OBJECTIVES: Recreational nitrous oxide (N2O) abuse is increasingly popular among youth. We report a systematic clinical, electrophysiological and biological follow-up of patients with neuropathy caused by N2O. METHODS: We retrospectively report seven patients with neuropathy attributed to N2O 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 N2O) 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 N2O 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.

Coenzyme Q10 is frequently reduced in muscle of patients with mitochondrial myopathy.

Coenzyme Q(10) (CoQ(10)) deficiency has been associated with an increasing number of clinical phenotypes. Whereas primary CoQ(10) defects are related to mutations in ubiquinone biosynthetic genes, which are now being unraveled, and respond well to CoQ(10) supplementation, the etiologies, and clinical phenotypes related to secondary deficiencies are largely unknown. The purpose of this multicenter study was to evaluate the frequency of muscle CoQ(10) deficiency in a cohort of 76 patients presenting with clinically heterogeneous mitochondrial phenotypes which included myopathy among their clinical features. A reliable diagnostic tool based on HPLC quantification was employed to measure muscle CoQ(10) levels. A significant proportion of these patients (28 over 76) displayed CoQ(10) deficiency that was clearly secondary in nine patients, who harbored a pathogenic mutation of mitochondrial DNA. This study provides a rationale for future therapeutic trials on the effect of CoQ(10) supplementation in patients with mitochondrial diseases presenting with myopathy among clinical features.