A 32-year-old woman from rural Maharashtra presents with a 3-day history of severe epistaxis and gum bleeding. She has no prior bleeding tendency. On examination, she is pale with petechiae on her lower extremities. Her platelet count is 8,000/μL, PT is 14 seconds (control 12), aPTT is 38 seconds (control 32), and fibrinogen is 280 mg/dL. A bone marrow aspirate shows hypercellular marrow with increased megakaryocytes. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis This patient presents with acute-onset severe thrombocytopenia with mucocutaneous bleeding in the absence of systemic features. ### Key Diagnostic Features **Key Point:** The hallmark of ITP is isolated thrombocytopenia with normal or increased bone marrow megakaryocytes, normal coagulation studies, and absence of microangiopathic hemolytic anemia. | Feature | ITP | TTP | DIC | HUS | |---------|-----|-----|-----|-----| | Platelet count | Severely ↓ | Severely ↓ | ↓ | ↓ | | PT/aPTT | Normal | Normal | ↑ | Normal | | Fibrinogen | Normal | Normal | ↓ | Normal | | Schistocytes | Absent | Present | Present | Present | | Renal function | Normal | Abnormal | Abnormal | Abnormal | | Fever | Absent | Present | Absent | Absent | | Bone marrow | ↑ Megakaryocytes | Normal | Normal | Normal | ### Why This Is ITP 1. **Isolated thrombocytopenia** with platelet count <20,000/μL 2. **Normal coagulation parameters** (PT, aPTT within normal limits) 3. **Normal fibrinogen** (280 mg/dL; normal 200–400 mg/dL) 4. **Hypercellular marrow with increased megakaryocytes** — indicates peripheral destruction, not bone marrow failure 5. **Absence of systemic features** — no fever, no renal dysfunction, no hemolytic anemia **Clinical Pearl:** In ITP, the bone marrow is the key finding that distinguishes it from bone marrow failure. The presence of adequate or increased megakaryocytes proves that thrombocytopenia is due to peripheral destruction (immune-mediated) rather than production failure. **High-Yield:** ITP is a diagnosis of exclusion. Once you rule out secondary causes (SLE, antiphospholipid syndrome, H. pylori, HIV) and confirm isolated thrombocytopenia with normal coagulation and increased megakaryocytes, ITP is the answer. **Mnemonic: PAINS** — Petechiae, Absent coagulopathy, Increased megakaryocytes, Normal fibrinogen, Severe thrombocytopenia.