# Marked increase in severe neurological disorders after nitrous oxide abuse: a retrospective study in the Greater Paris area

## TL;DR

Recreational nitrous oxide use has led to a significant rise in severe neurological disorders, especially among young adults in disadvantaged areas in Paris.

## Contribution

This study provides the first detailed analysis of the incidence and socio-economic patterns of nitrous oxide-induced neurological disorders in a large urban population.

## Key findings

- The incidence of nitrous oxide-induced neurological disorders peaked in 2021, particularly in 20-25-year-olds.
- Nitrous oxide-induced disorders were two to three times more common in socially disadvantaged areas.
- The incidence of nitrous oxide-induced myelopathy and neuropathy was significantly higher than similar inflammatory neurological disorders.

## Abstract

Recreational nitrous oxide (N2O) use has become more widespread worldwide, leading to an increase in myelopathies and peripheral neuropathies. The aim of this study was to describe clinical and socioeconomical characteristics of severe N2O-induced (NI) neurological disorders (NI-NDs), to determine its incidence in the Greater Paris area and to compare it with that of similar inflammatory neurological disorders.

We performed a retrospective multicentric cohort study of all adult patients with severe NI-NDs in the neurology and general internal medicine departments of the Greater Paris area from 2018 to 2021. The incidence was compared with that of non-NI-myelitis and Guillain–Barré syndrome (GBS) using a sample of 91,000 hospitalized patients sourced from health insurance data.

Among 181 patients, 25% had myelopathy, 37% had peripheral neuropathy and 38% had mixed disease. Most were aged between 20 and 25 years, lived in socially disadvantaged urban areas, and exhibited high rates of unemployment (37%). The incidence of NI-NDs increased during 2020 and reached a peak mid-2021. The 2021 incidence in 20–25-year-olds was 6.15 [4.72; 8.24] per 100,000 persons for NI-myelopathy and 7.48 [5.59; 9.37] for NI-peripheral neuropathy. This was significantly higher than for non-NI-myelitis (0.35 [0.02; 2.00]) and GBS (2.47 [0.64; 4.30]). The incidence of NI-NDs was two to three times higher in the most socially disadvantaged areas.

The recent increase in recreational N2O use has led to a rise in the incidence of severe NI-NDs, particularly in young adults with low socioeconomic status for whom NI-NDs strongly outweigh similar neurological disorders.

The online version contains supplementary material available at 10.1007/s00415-024-12264-w.