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A 32-year-old woman with a history of depression presented with an acute-onset gait disturbance. She could not stand without assistance. A neurologic examination revealed a positive Romberg's sign and dissociated sensory loss, which was suggestive of sensory ataxia. She had inhaled laughing gas from nearly 100 balloons to relieve her depressive mood 2 days before the onset of symptoms. A cervical MRI showed focal T2-hyperintensity at C1–2 level (Fig. 1). A cerebrospinal fluid examination was unremarkable. A serologic study showed that her hemoglobin level was 12.2 g/dL (normal range, 12–18 g/dL); MCV, 108.6 fL (80–99 fL); MCH, 35.5 pg (27–32 pg); vitamin B12, 94 pmol/L (156–672 pmol/L); homocysteine, >50 µmol/L (5–15 µmol/L). Ultimately, she was diagnosed with acute cervical myelopathy caused by vitamin B12 deficiency following the inhalation of laughing gas, and was treated with vitamin B12 replacement. The patient has been improving gradually with rehabilitation, and can stand up independently and walk alone with an ambulatory assistance device 3 months after treatment.
Laughing gas is the common name for nitrous oxide (N2O),1 and is typically used as an inhaled anesthetic agent in the field of surgery or dentistry.23 It is also used for recreational purposes due to its euphoric effects when inhaled.1-3 However, prolonged N2O abuse can lead to various neurologic manifestations including subacute combined degeneration, myeloneuropathy, or myelopathy without peripheral neuropathy due to vitamin B12 deficiency.4 Vitamin B12 is an essential cofactor in the synthesis of the myelin sheath, and can be inactivated irreversibly by exposure to N2O.13 Chronic myelopathy following long-term exposure to N2O has already reported,14 and subacute myelopathy can also occur 2 to 6 weeks after the surgery under anesthesia with N2O.2 Our patient presented with acute cervical myelopathy just 2 days after inhalation of laughing gas, which is relatively uncommon in N2O-induced myelopathy. To our knowledge, acute post-surgical myelopathy has only been once reported after anesthesia with N2O.2
In summary, our case highlights that N2O can cause acute myelopathy by laughing gas abuse in the absence of anesthesia with N2O. Further study is needed for determining the relation between the exposure of laughing gas and onset of neurologic symptoms.
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