A Case of Subacute Combined Degeneration of Spinal Cord Diagnosed by Vitamin B12 Administration Lowering Methylmalonic Acid

Subacute combined degeneration of the spinal cord (SCDS) is a neurodegenerative disease characterized by subacute progression in the central and peripheral nervous systems mainly caused by vitamin B12 deficiency. It is known that typical SCDS is frequently accompanied by megaloblastic anemia and increased serum methylmalonic acid (MMA) or homocysteine (Hcy) levels on laboratory findings, and marked abnormalities on spinal cord magnetic resonance imaging (MRI). A 45-year-old woman was admitted to our hospital with a 2-year history of worsening mild weakness, numbness in bilateral lower limbs, and gait disturbance. On admission, as laboratory findings, blood count showed macrocytosis without anemia, and biochemical tests showed mild reduction in total serum vitamin B12 level and no increase of MMA and Hcy levels; there were no abnormal findings on spinal cord MRI. After administration of vitamin B12, her sensorimotor symptoms were improved and laboratory examination showed that macrocytosis was improved, serum vitamin B12 was increased, and serum MMA levels were decreased. This improved clinical course and the laboratory findings following vitamin B12 administration confirmed the diagnosis of SCDS due to vitamin B12 deficiency. SCDS presents with highly variable symptoms and laboratory findings, and observation of MMA levels and neurologic symptoms before and after vitamin B12 administration may be useful for diagnosing SCDS.