Professional and Linguistic Assessments Board (PLAB) Practice Exam

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What deficiency is associated with subacute combined degeneration of the cord?

  1. Vitamin D

  2. Vitamin B12

  3. Folic acid

  4. Iron

The correct answer is: Vitamin B12

Subacute combined degeneration of the cord is primarily associated with a deficiency of vitamin B12, also known as cobalamin. This condition is characterized by the degeneration of both the posterior columns and the lateral corticospinal tracts in the spinal cord. Vitamin B12 is essential for the proper functioning and maintenance of myelin, the protective sheath surrounding nerve fibers. A deficiency leads to demyelination, which ultimately affects the conduction of nerve impulses. Individuals with vitamin B12 deficiency may present with a variety of neurological symptoms, including sensory disturbances (such as numbness or tingling), weakness, and balance issues, as well as signs consistent with upper and lower motor neuron involvement. Other symptoms may include cognitive changes and a specific type of anemia known as megaloblastic anemia. The other nutrients listed, while important for overall health, do not specifically lead to the characteristic features of subacute combined degeneration of the cord. Vitamin D plays a crucial role in bone health and calcium homeostasis but does not directly impact the nervous system in this way. Folic acid is important for DNA synthesis and also helps prevent megaloblastic anemia, but it’s the deficiency in vitamin B12 that uniquely causes the neurological degeneration described. Iron is vital for hemoglobin production