## Clinical Diagnosis This patient has **drug-induced agranulocytosis** secondary to methimazole—a life-threatening complication occurring in ~0.02% of methimazole-treated patients, typically within the first 3 months of therapy. ### Key Clinical Features | Feature | Finding | Significance | |---------|---------|---------------| | **Fever + Pharyngitis + Oral Ulcers** | Present | Classic triad of agranulocytosis | | **WBC 1.2 × 10⁹/L** | Severe leukopenia | Normal >4.5 × 10⁹/L | | **Neutrophils 15%** | Severe neutropenia | Normal >40% | | **Timing** | 6 weeks post-methimazole | Peak risk window | **Key Point:** Agranulocytosis is an **idiosyncratic reaction** (not dose-dependent) and is a medical emergency with mortality ~5–10% if untreated. ## Management Algorithm ```mermaid flowchart TD A[Fever + Pharyngitis + WBC 1.2 on Methimazole]:::urgent --> B[STOP Methimazole Immediately]:::action B --> C[Blood Cultures + Broad-Spectrum Antibiotics]:::action C --> D[Hematology Consultation]:::action D --> E{Bone Marrow Exam if Indicated}:::decision E -->|Hypoplasia| F[Supportive Care + G-CSF Consider]:::action E -->|Normal/Reactive| G[Continue Antibiotics, Monitor Recovery]:::action A --> H[Switch Antithyroid: PTU or RAI/Surgery]:::action ``` ### Rationale for Correct Answer **High-Yield:** The management triad for antithyroid-induced agranulocytosis: 1. **Stop the offending drug immediately** — methimazole must be discontinued at once; continuing risks sepsis and death. 2. **Empiric broad-spectrum antibiotics** — fever + severe neutropenia = presumed bacterial infection until proven otherwise; blood cultures guide later de-escalation. 3. **Hematology referral** — assessment for bone marrow involvement, need for G-CSF, and monitoring of neutrophil recovery. **Clinical Pearl:** Once methimazole-induced agranulocytosis occurs, **cross-sensitivity with PTU is ~50%**; therefore, definitive therapy (radioactive iodine or thyroidectomy) is preferred over switching to another antithyroid drug. ### Why Propranolol Monotherapy Is Insufficient Propranolol controls symptoms (tachycardia, tremor) but does **not reduce thyroid hormone synthesis**. The patient is currently euthyroid biochemically, but without antithyroid therapy, hyperthyroidism will recur within weeks. Propranolol alone is a bridge, not definitive management in this acute crisis. [cite:Harrison 21e Ch 397; KD Tripathi 8e Ch 41]
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