Unhappy Balloon, Nitrous Oxide-induced Subacute Combined Degeneration of the Spinal Cord: A Review of Case Series

Abstract

Background: The younger generation in Korea easily exposed to nitrous oxide (N<sub>2</sub>O) under the name “Happy Balloon” may abuse it. N<sub>2</sub>O can irreversibly oxidize vitamin B<sub>12</sub> and cause abnormal hematopoiesis or nervous system toxicity such as subacute combined degeneration (SCD). The objective of this study was to assist in early diagnosis of N<sub>2</sub>O-induced SCD of spinal cord by characterizing its clinical manifestations.Methods: Four patients with myelopathy after abusing N<sub>2</sub>O were enrolled. To characterize N<sub>2</sub>O-induced myelopathy, previously reported cases of N<sub>2</sub>O-induced SCD were searched through PubMed and KoreaMed. Collected cases and our four patients were analyzed.Results: A total of 30 patients with N<sub>2</sub>O-induced myelopathy (26 males and 4 females with mean age of 24 years) were analyzed. These patients took a median dose of 650 canisters for a median duration of 3.5 months. All patients presented sensory disturbances, which involved the lower extremities more frequently (100%) than the upper extremities (63.3%). Gait ataxia (76.7%), weakness in the upper (23.3%) and lower (36.7%) extremities, bladder symptoms (26.7%), Rhomberg sign (43.3%), and Lhermitte’s phenomenon (10.0%) were observed. Serum vitamin B12 levels were decreased in many (63.3%) patients and homocysteine levels were elevated in all. Of 20 patients who underwent magnetic resonance imaging (MRI) of the spine, 19 had abnormal findings. Three patients presented with contrast enhancement in lesions.Conclusions: We strongly recommend that history of N<sub>2</sub>O abuse should be asked for young patients with suspected myelopathy, especially those presenting with gait ataxia and sensory disturbances suggesting posterior column dysfunction and those presenting long-segment lesion involving the upper cervical cord on MRI.