A 32-year-old woman presents with a 6-month history of menorrhagia and recurrent epistaxis. On examination, she has petechiae over the lower extremities and oral mucosa. Laboratory investigations reveal: hemoglobin 9.2 g/dL, platelet count 18,000/μL, PT 12 seconds (normal 11–13.5 s), aPTT 32 seconds (normal 24–35 s), bleeding time 8 minutes (normal 2–9 min). Bone marrow examination shows normocellular marrow with adequate megakaryocytes. Which of the following is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Immune Thrombocytopenia (ITP) ### Key Clinical Features **Key Point:** The clinical triad of severe thrombocytopenia (18,000/μL), mucocutaneous bleeding (epistaxis, petechiae, menorrhagia), and **normal coagulation studies** with **adequate bone marrow megakaryocytes** is pathognomonic for ITP. ### Laboratory Interpretation | Finding | ITP | TTP | DIC | HUS | |---------|-----|-----|-----|-----| | Platelet count | Severe ↓ | Severe ↓ | Severe ↓ | Severe ↓ | | PT/aPTT | Normal | Normal | Prolonged | Normal | | Fibrinogen | Normal | Normal | ↓↓ | Normal | | Schistocytes | Absent | Present | Present | Present | | Renal function | Normal | Abnormal | Abnormal | Abnormal | | Megakaryocytes | Adequate/↑ | Normal | ↓ | Normal | **High-Yield:** ITP is a diagnosis of exclusion. The presence of: - Severe thrombocytopenia - Normal PT/aPTT (ruling out DIC) - Adequate bone marrow megakaryocytes (ruling out bone marrow failure) - Absence of microangiopathic hemolytic anemia (no schistocytes mentioned) - Absence of renal/neurological involvement (ruling out TTP/HUS) All point definitively to ITP. ### Pathophysiology ITP is an autoimmune condition where IgG antibodies target platelet surface antigens (GPIIb/IIIa, GPIb/IX), leading to: 1. Platelet destruction in the spleen 2. Impaired platelet production (secondary) 3. Bleeding manifestations when platelet count <30,000/μL **Clinical Pearl:** The bleeding time is at the upper limit of normal because platelet *function* is preserved—only the *number* is reduced. This distinguishes ITP from qualitative platelet disorders (von Willebrand disease, Bernard-Soulier syndrome). ### Management Approach ```mermaid flowchart TD A[Confirmed ITP diagnosis]:::outcome --> B{Platelet count & bleeding?}:::decision B -->|>30k, no bleeding| C[Observation/Monitor]:::action B -->|<30k OR active bleeding| D[First-line: Corticosteroids]:::action D --> E{Response at 2-4 weeks?}:::decision E -->|Yes| F[Taper & maintain]:::action E -->|No/Relapse| G[IVIG or Anti-D]:::action G --> H{Sustained response?}:::decision H -->|No| I[Splenectomy/TPO agonist]:::action ``` **High-Yield:** First-line therapy is **corticosteroids** (prednisolone 1 mg/kg/day), which work by suppressing antibody production and reducing splenic destruction.