A 32-year-old woman from Delhi presents with a 3-month history of easy bruising, petechiae on her lower extremities, and menorrhagia. She denies fever, lymphadenopathy, or hepatosplenomegaly. Laboratory investigations show: Hemoglobin 10.2 g/dL, WBC 7,200/μL, platelet count 18,000/μL, PT 12 s, aPTT 32 s, fibrinogen 280 mg/dL. Bone marrow examination reveals normal cellularity with increased megakaryocytes. Peripheral blood smear shows no schistocytes or abnormal cells. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Immune Thrombocytopenia (ITP) ### Key Diagnostic Features **Key Point:** ITP is characterized by isolated thrombocytopenia with normal bone marrow megakaryocytes and absence of other systemic features. This patient presents with the classic triad of ITP: 1. **Isolated thrombocytopenia** (18,000/μL) with normal hemoglobin and WBC 2. **Increased megakaryocytes** on bone marrow examination—indicating appropriate bone marrow response 3. **Normal coagulation studies** (PT, aPTT, fibrinogen)—ruling out consumptive coagulopathy ### Differential Diagnosis Table | Feature | ITP | TTP | DIC | Drug-induced | |---------|-----|-----|-----|---------------| | **Platelet count** | Severely ↓ | Severely ↓ | ↓↓ | Variable | | **Schistocytes** | Absent | Present | Present | Absent | | **Coagulation studies** | Normal | Normal | Abnormal (↑PT, ↑aPTT, ↓Fib) | Normal | | **Fibrinogen** | Normal | Normal | ↓↓ | Normal | | **Bone marrow** | ↑ Megakaryocytes | Normal | Normal | ↑ Megakaryocytes | | **Fever/MAHA** | Absent | Present (pentad) | Variable | Absent | **High-Yield:** The **absence of schistocytes** and **normal coagulation parameters** are the critical findings that exclude TTP and DIC. ### Pathophysiology ITP results from **autoimmune destruction** of platelets by IgG antibodies against platelet surface antigens (GPIIb/IIIa, GPIb-IX). The bone marrow responds with increased megakaryopoiesis, but platelet survival is shortened (hours instead of 7–10 days). **Clinical Pearl:** Menorrhagia in a young woman with thrombocytopenia is a common presenting feature of ITP and may be the reason for the secondary iron deficiency anemia (Hb 10.2 g/dL). ### Why Bone Marrow Shows Increased Megakaryocytes The bone marrow is **functioning normally**—it detects low platelet count and increases megakaryopoiesis in an attempt to compensate. This is a key distinguishing feature from bone marrow failure syndromes (aplastic anemia, MDS) where megakaryocytes would be normal or decreased. **Mnemonic: PAINS of ITP** — **P**etechiae, **A**utoimmune, **I**solated thrombocytopenia, **N**ormal bone marrow, **S**plenomegaly (variable).