ROSH Gastrointestinal Practice Exam

What vitamin deficiency is likely in a patient with dementia, diarrhea, and a hyperpigmented rash after isoniazid treatment?

1. Vitamin B1

2. Vitamin B12

3. Vitamin B3

4. Vitamin B9

The correct answer is: Vitamin B3

The symptoms described—dementia, diarrhea, and a hyperpigmented rash—are characteristic of a deficiency in vitamin B3, also known as niacin. Isoniazid, a medication used primarily to treat tuberculosis, is known to interfere with the metabolism of this vitamin. It can inhibit the enzyme that converts tryptophan into niacin, leading to reduced levels of vitamin B3 in the body. In the context of the clinical presentation, dementia can occur as a neurological manifestation of niacin deficiency, while diarrhea and dermatitis (the hyperpigmented rash) are classic symptoms of pellagra, which is the condition associated with severe niacin deficiency. This condition manifests with the "three D's": Dermatitis, Diarrhea, and Dementia, reinforcing the association between niacin deficiency and the symptoms presented after isoniazid treatment. Other vitamins listed would not typically present with this triad of symptoms in the context of isoniazid use, making niacin deficiency the most plausible explanation for the clinical scenario described.