The disease is a degenerative disease of the nervous system caused by vitamin B12 deficiency. It has a chronic or subacute onset and may present early with sensory abnormalities in the feet or extremities (tingling, numbness) and may progress to spinal symptoms (sensory ataxia, sensation of stepping on the ground like cotton, worse at night when there is little light, unsteady gait, spastic paraplegia), sometimes requiring differentiation from hereditary spastic paraplegia. However, subacute combined degeneration has no family history, often has diseases or factors that cause vitamin B12 deficiency (long-term strict vegetarian diet, major gastrectomy, gastrointestinal malabsorption), has profound sensory disturbances and sensory ataxia, is accompanied by megaloblastic anemia, has low serum vitamin B12 levels, and has a significant effect of vitamin B12 treatment.