A patient given one of the following drug develops low grade fever, muscle and joint ache, chest pain and skin rashes. Lab investigations showed presence of antihistone antibodies. Symptoms however subsided after discontinuation of the drug. Which is the drug that caused the reaction?

**Core Concept**
The patient's symptoms and lab findings are indicative of Drug-Induced Lupus Erythematosus (DILE), a syndrome that mimics systemic lupus erythematosus (SLE) but is caused by certain medications. This condition is characterized by the presence of antihistone antibodies and can resolve upon discontinuation of the offending drug.

**Why the Correct Answer is Right**
The patient's symptoms, including low-grade fever, muscle and joint ache, chest pain, and skin rashes, are consistent with DILE. The presence of antihistone antibodies further supports this diagnosis. The fact that symptoms resolved after discontinuation of the drug is also characteristic of DILE, which is often reversible upon removal of the causative agent. Certain medications, such as hydralazine, procainamide, and isoniazid, are known to cause DILE.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.

**Option B:** This option is not provided.

**Option C:** This option is not provided.

**Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
DILE can mimic other autoimmune diseases, such as SLE, and can be challenging to diagnose. However, the presence of antihistone antibodies and the resolution of symptoms upon discontinuation of the offending drug can help distinguish DILE from other conditions.

**Correct Answer:** A (Hydralazine)

✓ Correct Answer: A. Hydralazine