**Core Concept**
Agranulocytosis is a potentially life-threatening condition characterized by a severe reduction in the number of granulocytes (a category of white blood cells) in the blood, leading to increased susceptibility to infections. This condition is often associated with the use of certain medications that affect bone marrow function.

**Why the Correct Answer is Right**
Agranulocytosis is a well-documented side effect of several medications, including certain antithyroid drugs, such as methimazole and propylthiouracil. These medications can induce agranulocytosis by suppressing the production of granulocytes in the bone marrow. The exact mechanism is not fully understood, but it is thought to involve the inhibition of the enzyme thyroperoxidase, which is essential for the production of thyroid hormones.

**Why Each Wrong Option is Incorrect**
**Option A:** Not a commonly reported cause of agranulocytosis.
**Option B:** Not a known side effect of this medication.
**Option C:** Associated with a different type of hematologic toxicity, such as anemia or thrombocytopenia.

**Clinical Pearl / High-Yield Fact**
Methimazole and propylthiouracil are two antithyroid medications that are commonly used to treat hyperthyroidism. However, they have a rare but serious side effect of agranulocytosis, which can occur at any time during treatment. Patients on these medications should be closely monitored for signs of infection or other hematologic abnormalities.

**Correct Answer: D.**