BACKGROUND AND PURPOSE: A resurgence in recreational misuse of nitrous oxide has been observed in the post-coronavirus disease 2019 (COVID) pandemic era and consequently there has been a surge in cases of nitrous oxide-induced subacute combined degeneration of the cord (NO-SACD). It is essential that physicians have an awareness of clinical history, neurologic findings, laboratory investigations, and characteristic features on MR imaging that may suggest a diagnosis of NO-SACD.

MATERIALS AND METHODS: This retrospective, hospital-based case series was conducted in a tertiary medical referral center and 1 of 2 National Neuroscience Centers in Ireland. Retrieval of cases was achieved by a keyword search of a radiology PACS archive, using the terms such as "subacute combined degeneration of the cord" and "SACD" to search clinical indications for MR imaging and radiology reports at the institution from July 1, 2012 to December 31, 2024.

RESULTS: Thirty-three patients underwent MRI investigations for suspected subacute combined degeneration of the cord. Twenty-five reported nitrous oxide use. Fourteen of those with reported nitrous oxide use and clinical symptoms had MRI findings suggestive of subacute combined degeneration of the cord. Most prominent symptoms were distal paresthesia (100%), weakness (52%), and ataxia (36%). All cases of NO-SACD occurred between 2020 and 2024. The cervical cord was affected in all 14 MRI-positive patients with a characteristic inverted V sign synonymous with subacute combined degeneration of the cord identified in all 14 (100%).

CONCLUSIONS: This case series reflects the growing incidence and prevalence of NO-SACD. Presentations occurring exclusively between 2020-2024 correlate with the COVID-19 pandemic and its aftermath, which aligns with reported increased misuse across Europe at this time. MRI cervicothoracic spine with T1, T2, and STIR sagittal and T2 axial sequences should suffice for radiologic diagnosis and should be interpreted in conjunction with clinical, laboratory, and, in some cases, electrophysiologic findings.