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:

**Core Concept**
Isoniazid-induced peripheral neuropathy and other systemic effects are due to pyridoxine (vitamin B6) deficiency. Isoniazid inhibits pyridoxine kinase, an enzyme required for the activation of pyridoxine.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with pyridoxine deficiency, which is caused by isoniazid's inhibition of pyridoxine kinase. This leads to impaired synthesis of pyridoxal phosphate, a crucial co-factor for many enzymes, including those involved in neurotransmitter synthesis. As a result, the patient experiences peripheral neuropathy, memory disturbances, and gastrointestinal symptoms. The skin rash is likely a manifestation of pyridoxine deficiency as well.

**Why Each Wrong Option is Incorrect**
**Option A:** Lactic acidosis is a known side effect of isoniazid, but it does not explain the patient's symptoms.
**Option B:** Hypersensitivity reactions to isoniazid can cause rash and fever, but they do not account for the patient's memory disturbances and diarrhea.
**Option C:** Isoniazid-induced hepatitis is a serious side effect, but it does not explain the patient's neurological and gastrointestinal symptoms.

**Clinical Pearl / High-Yield Fact**
Isoniazid-induced peripheral neuropathy can be prevented with pyridoxine supplementation. Patients on isoniazid should receive pyridoxine prophylaxis to prevent this potentially debilitating side effect.

**Correct Answer: B. Hypersensitivity reaction to isoniazid.**

✓ Correct Answer: B. Niacin deficiency