How to distinguish Guillain-Barre syndrome from nitrous oxide-induced neuropathy: A 2-year, multicentric, retrospective study

Background: Recreational use of nitrous oxide (N2O) has dramatically increased in recent years, resulting in numerous cases of acute sensorimotor tetraparesis secondary to nitrous oxide-induced neuropathy (N(2)On). Challenging clinical features can mimic Guillain-Barre syndrome (GBS), the main differential diagnosis upon admission. The most sensitive biomarkers for distinguishing between these two conditions remain to be determined.Methods: Fifty-eight N(2)On patients from three referral centers were retrospectively included over a 2-year period and compared to GBS patients hospitalized during the same timeframe (47 patients). Collected demographic, clinical, biological, and electrophysiological data were compared between the two groups.Results: The typical N(2)On clinical pattern included distal sensorimotor deficit in lower limbs with absent reflexes, proprioceptive ataxia, and no cranial involvement (56.7% of our cohort). Misleading GBS-like presentations were found in 14 N(2)On patients (24.1%), and 13 patients (22.4%) did not report N2O use during initial interview. Only half the N(2)On patients presented with reduced vitamin B12 serum levels upon admission. A slightly increased cut-off (<200 pmol/L) demonstrated 85.1% sensitivity and 84.5% specificity in distinguishing N(2)On from GBS. Only 6.9% of N(2)On patients met the criteria for primary demyelination (p < 0.01), with only one presenting conduction blocks. A diagnostic algorithm combining these two biomarkers successfully classified all GBS-like N(2)On patients.Conclusions: Vitamin B12 serum level < 200 pmol/L cut-off and conduction blocks in initial electrophysiological study are the two most sensitive biomarkers for rapidly distinguishing N(2)On from GBS patients. These two parameters are particularly useful in clinically atypical N(2)On with GBS-like presentation.