American Board of Psychiatry and Neurology (ABPN) Practice Exam

Subacute combined degeneration of the spinal cord is primarily associated with a deficiency in Vitamin B12. This condition results from the involvement of both the dorsal columns and lateral corticospinal tracts, leading to serious neurological symptoms such as ataxia, muscle weakness, and sensory disturbances. Vitamin B12 is crucial for proper myelin synthesis and maintenance in the nervous system; a deficiency disrupts this process, particularly affecting the spinal cord's structure and function.

While other vitamins listed play various roles in neurological health, their deficiencies do not lead specifically to subacute combined degeneration. For example, Vitamin B1 (thiamine) deficiency is primarily linked to Wernicke's encephalopathy and Beriberi, while Vitamin B6 is important in neurotransmitter synthesis but is not directly involved in the degeneration of spinal cord structures. Folic acid is essential for DNA synthesis and red blood cell formation, but its deficiency does not produce the same neurological complications seen with Vitamin B12 deficiency. Thus, the role of Vitamin B12 is distinct and critical in the pathophysiology of subacute combined degeneration.