This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins and Minerals, Subject name: Biochemistry
A 38 year old female patient was on Isoniazid therapy for tuberculosis. She developed rashes on the exposed pas of her body. She has disoriented memory. Family members gives history of diarrhea also. What is the diagnosis: 
Select and explain. 
A. Tuberculosis skin lesions, B. Niacin deficiency, C. Isoniazid neuropathy, D. Some other drug has caused this
B: Niacin deficiency
Answer: B: Niacin deficiency 
Explanation: Isoniazid inhibits the endogenous synthesis of niacin. So the patient has developed pellagra i.e. dermatitis, dementia and diarrhea. Prolonged treatment with isoniazid leads to pyridoxine deficiency, which is required for endogenous synthesis of niacin.