Abstract: Objective To investigate the etiology, clinical features, laboratory examinations and imaging characteristics of subacute combined degeneration (SCD) of the spinal cord. 
Methods Clinical data of patients diagnosed with SCD in our department from May 2015 to October 2022 were analyzed retrospectively. In this study, 22 males and 18 females were included. According to the etiology, the patients were divided into vitamin B12 deficiency group (n=34) and nitrous oxide (N2O) abuse group (n=6). 
Results The clinical course of SCD was subacute or chronic. Most patients began with paresthesia and/or limb weakness. Cognitive impairment occurred in a small number of patients and was more significant in N2O abuse group. Laboratory tests showed decreased vitamin B12 level in most patients, accompanied by decreased folate, megaloblastic anemia, hyperhomocysteinemia, and positive anti-internal factor antibodies or anti-parietal cell antibodies. Spinal MRI revealed that the lesions mostly involved the posterior and lateral cord of cervical and thoracic spinal cord, which was characterized by an "inverted V sign" on the axial T2WI. Most patients achieved improvement in symptoms and signs after vitamin B12 treatment. 
Conclusion SCD of the spinal cord is closely related to vitamin B12 deficiency. N2O abuse is a common cause in young patients with SCD. The clinical manifestations of SCD are complicated and varied, and spinal "inverted V sign" is an important evidence for diagnosis. Early diagnosis and standard treatment are the key to obtaining a good prognosis. 

Key words: subacute combined degeneration of the spinal cord, vitamin B12, nitrous oxide