[Clinical features of long segmental myelopathy caused by nitrous oxide]

To analyze the clinical and imaging characteristics of the neurological damage caused by nitrous oxide (N₂O).

In the study, 10 patients in the Department of Neurology of China-Japan Friendship Hospital from October 2015 to February 2018 were retrospectively analyzed for the demographic data, the history of inhaled N₂O, clinical features, blood examination, electrophysiological examination, spinal magnetic resonance imaging and therapeutic efficacy profiles.

The male-to-female ratio was 4:6 and it presented with an age-of-onset 17-26 years [the average age: (20.80±3.12) years]. The time from inhaled N₂O to onset was 1 month to 1 year [the average time: (6.95±4.19) months]. Paralysis in all the patients and numbness in 9 patients were the main clinical features, while positive Lhermitte's sign in 3 patients, urinary and defecation disturbance in 4 patients were also found. Blood examination indicated anemia in 2 patients, giant cell anemia in 1 case and small cell hypochromic anemia in 1 case. 3 cases had been treated with vitamin B12 in an external hospital, and the other 7 cases had abnormal increase in homocysteine levels. Electrophysiological examinations showed sensory and motor nerve involvement in 9 patients, and motor nerve involvement in 1 patient. The severity of lower extremity lesion was significantly heavier than that of upper extremity. Spinal magnetic resonance imagings showed that long segmental lesions were present in the cervical spinal cord of all the patients, 3 cases with long segmental lesions of the thoracic cord and 2 cases with spinal cord swelling. In 6 cases, the horizontal axis had an "inverted V-type" T2 high signal, 1 case was classified as "crescent", and 3 cases were "eight-shaped". The symptoms in these 10 cases were alleviated in varying degrees after stopping the inhalation of nitrous oxide, actively supplementing high doses of vitamin B12 and doing early rehabilitation exercises.

Myelopathy with nitrous oxide presents as paralysis and numbness in limb extremities. In imaging, cervical spinal cord damage is common, accompanied by thoracic spinal cord damage. The horizontal axis is more common in the "inverted V-type". Treatment with high doses of vitamin B12 is effective.