A 28-year-old woman from Delhi presents with a 3-day history of severe epistaxis and gum bleeding. She reports menarche at age 14 with heavy menstrual bleeding requiring transfusion twice. On examination, she has petechiae on lower limbs and oral mucosa. Laboratory investigations show: Hb 9.2 g/dL, platelet count 18,000/μL, PT 12 sec (control 12), aPTT 28 sec (control 28), bleeding time 8 minutes (control 3–8). Bone marrow examination reveals normocellular marrow with normal megakaryocytes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Immune Thrombocytopenia (ITP) ### Key Clinical Features **Key Point:** The diagnosis of ITP rests on the triad of (1) thrombocytopenia, (2) normal or increased bone marrow megakaryocytes, and (3) absence of secondary causes. This patient presents with: - Severe thrombocytopenia (18,000/μL) - Mucocutaneous bleeding (epistaxis, gum bleeding, petechiae) - **Normal coagulation studies** (PT and aPTT normal) - **Normocellular bone marrow with normal megakaryocytes** — rules out production defects - **Prolonged bleeding time** — reflects platelet dysfunction or severe thrombocytopenia - **Lifelong history** of heavy menstrual bleeding since menarche — suggests chronic immune-mediated platelet destruction ### Why the Coagulation Studies Are Normal ITP is a **platelet disorder**, not a coagulation factor deficiency. PT and aPTT depend on factors II, V, VII, X (PT) and XII, XI, IX, VIII (aPTT), which are normal in ITP. Bleeding time is prolonged because platelet count is <20,000/μL and/or platelet function is impaired by antibody coating. ### Pathophysiology 1. Autoantibodies (IgG) bind to platelet surface antigens (GPIIb/IIIa, GPIb/IX) 2. Antibody-coated platelets are opsonized and cleared by splenic macrophages 3. Megakaryocytes increase in response (compensatory), but destruction exceeds production 4. Result: **peripheral destruction** with **normal or increased marrow reserves** ### Differential Diagnosis Table | Feature | ITP | DIC | TTP | Bernard–Soulier | |---------|-----|-----|-----|------------------| | **Platelet count** | ↓↓ | ↓↓ | ↓↓ | ↓ (mild–moderate) | | **PT/aPTT** | Normal | ↑↑ | Normal | Normal | | **Fibrinogen** | Normal | ↓↓ | Normal | Normal | | **Schistocytes** | Absent | Present | Present | Absent | | **Bone marrow** | ↑ Megakaryocytes | Normal | Normal | Normal | | **Bleeding time** | ↑ | ↑ | ↑ | ↑↑ (marked) | | **Trigger** | Autoimmune | Sepsis, DKA, malignancy | Shiga toxin, TTP-ADAMTS13 | Congenital | **High-Yield:** In ITP, **coagulation studies are always normal**. If PT or aPTT is prolonged, think DIC or liver disease, not ITP. ### Clinical Pearl The **normocellular bone marrow with increased megakaryocytes** is the gold standard for confirming peripheral destruction rather than bone marrow failure. This finding is pathognomonic for ITP in the presence of thrombocytopenia and normal coagulation studies. ### Management Implications - **First-line:** Corticosteroids (prednisolone 1 mg/kg/day) or IVIG (2 g/kg over 2–5 days) - **Second-line:** Splenectomy (if corticosteroid-responsive), rituximab, TPO-mimetics (eltrombopag, romiplostim) - **Avoid:** NSAIDs, anticoagulants (will worsen bleeding) [cite:Robbins 10e Ch 13]