A 28-year-old woman presents to the emergency department with spontaneous bleeding from gums and petechial rash over lower limbs for 2 days. She denies recent fever, drug intake, or family history of bleeding disorders. On examination, she is afebrile with scattered petechiae and ecchymoses. Laboratory investigations reveal: Hemoglobin 11.2 g/dL, WBC 7,200/μL, Platelets 8,000/μL, PT 12 sec (control 12 sec), aPTT 28 sec (control 28 sec), Bleeding time 8 minutes. Bone marrow examination shows normocellular marrow with increased megakaryocytes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Immune Thrombocytopenic Purpura ### Key Clinical Features **Key Point:** The diagnosis of ITP is based on the triad of thrombocytopenia, normal coagulation studies, and increased bone marrow megakaryocytes in the absence of systemic disease. This patient presents with: - Severe thrombocytopenia (8,000/μL) with spontaneous mucosal bleeding and petechiae - Normal PT and aPTT (indicating intact coagulation cascade) - Prolonged bleeding time (expected with severe thrombocytopenia) - Normocellular bone marrow with **increased megakaryocytes** — the hallmark finding - Absence of fever, hemolysis, or renal dysfunction - No recent drug exposure or systemic illness ### Pathophysiology ITP is an autoimmune disorder characterized by: 1. Production of IgG antibodies against platelet surface antigens (GPIIb/IIIa, GPIb-IX) 2. Complement-mediated platelet destruction in the spleen and liver 3. Increased megakaryocytic activity attempting to compensate for platelet loss 4. Preserved coagulation function (PT, aPTT normal) ### Diagnostic Criteria for ITP | Feature | ITP | TTP | DIC | |---------|-----|-----|-----| | **Platelet count** | <30,000 (often <10,000) | <30,000 | <100,000 | | **PT/aPTT** | Normal | Normal | Prolonged | | **Fibrinogen** | Normal | Normal | Low | | **Schistocytes** | Absent | Present (MAHA) | Present | | **Fever** | Absent | Present | Variable | | **Renal dysfunction** | Absent | Present (AKI) | Present | | **Bone marrow** | Increased MKs | Normal | Normal | | **LDH/Bilirubin** | Normal | Elevated | Elevated | **High-Yield:** The presence of **increased megakaryocytes on bone marrow examination** definitively excludes bone marrow failure as the cause of thrombocytopenia and strongly supports ITP. ### Why Other Diagnoses Are Excluded **Clinical Pearl:** The **pentad of TTP** (thrombocytopenia, microangiopathic hemolytic anemia, fever, renal dysfunction, neurological symptoms) is absent here — no fever, no hemolysis, no renal involvement, and no schistocytes. DIC would show prolonged PT/aPTT, low fibrinogen, and elevated D-dimer — all absent in this patient. ### Management Approach ```mermaid flowchart TD A[Confirmed ITP<br/>Platelet <30,000]:::outcome --> B{Bleeding symptoms?}:::decision B -->|Yes| C[First-line: Corticosteroids<br/>or IVIG]:::action B -->|No| D[Observation vs<br/>Corticosteroids]:::action C --> E{Response in 2-4 weeks?}:::decision E -->|Yes| F[Continue steroid taper]:::action E -->|No| G[Add second-line agent:<br/>Splenectomy, TPO-RA,<br/>or Rituximab]:::action ``` **Key Point:** First-line treatment for symptomatic ITP is corticosteroids (prednisolone 1 mg/kg/day) or IVIG (2 g/kg over 2–5 days), with response expected in 2–4 weeks.