Clinical and MRI Differences Between Patients With Subacute Combined Degeneration of the Spinal Cord Related vs. Unrelated to Recreational Nitrous Oxide Use: A Retrospective Study

Objective: To explore the clinical and imaging characteristics of subacute combined degeneration of the spinal cord (SCD) related to recreational nitrous oxide (N(2)O) use. Methods: Clinical and imaging data were retrospectively collected from patients with SCD related to recreational N(2)O use who were diagnosed and treated at Shengjing Hospital of China Medical University from January 2016 to June 2020. The clinical and imaging features of patients with recreational N(2)O-related SCD were compared with those of patients with N(2)O-unrelated SCD, who were diagnosed and treated during the same period of time. Results: The study enrolled 50 patients (male/female: 22/28, age: 21.4 ± 4.7 years) with N(2)O-related SCD and 48 patients (male/female: 27/21, age: 62.0 ± 11.4 years) with SCD unrelated to N(2)O use. The most common signs/symptoms of the patients in both groups were limb numbness and weakness and unsteady gait, but the incidence of limb weakness, unsteady gait, disorders of urination and defecation, anorexia, reduced deep sensation in lower limbs, ataxia, and positive Babinski sign were lower in the N(2)O-related SCD group than those in the N(2)O-unrelated SCD group (P < 0.05). The functional disability rating score of patients in the N(2)O-related SCD group (median: 3, IQR: 2–5) was also significantly lower than the score in the N(2)O-unrelated SCD group (median: 5, IQR: 4–7) (P < 0.05). The serum vitamin B12 level was significantly lower in the N(2)O-unrelated SCD group (median: 96 pg/mL, IQR: 50–170 pg/mL) than the level in the N(2)O-related SCD group (median: 218 pg/mL, IQR:121–350 pg/mL) (P < 0.05), while both groups had similarly increased levels of homocysteine (P > 0.05). Compared with the N(2)O-unrelated SCD patients, more patients with N(2)O-related SCD had abnormal spinal magnetic resonance imaging (MRI) scans (80.0 vs. 64.2%). The patients with N(2)O-related SCD also had wider spinal lesions on sagittal MRI (5.3 ± 0.8 mm vs. 4.2 ± 1.0 mm), fewer spinal segments with lesions (median: 5, IQR: 4–6 segments vs. median: 6, IQR: 5–7.5 segments), and a higher incidence of the inverted V sign on axial MRI (72.0 vs. 31.2%) (all P < 0.05). Conclusion: The recreational use of N(2)O has become an important cause of SCD in young patients. Compared with the N(2)O-unrelated SCD patients, the N(2)O-related SCD patients had less severe clinical presentations, less obvious decrease in serum VB12 levels, and more obvious MRI changes.