A 32-year-old woman from Delhi presents with a 3-day history of spontaneous bleeding from gums, epistaxis, and petechial rash over lower limbs. She denies recent infections or drug use. Vital signs are stable. Laboratory investigations show: Hb 10.2 g/dL, platelet count 8,000/μL, PT 12 s (control 12 s), aPTT 32 s (control 32 s), fibrinogen 280 mg/dL. Peripheral blood smear shows no schistocytes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Immune Thrombocytopenia (ITP) ### Key Distinguishing Features **Key Point:** ITP is a diagnosis of exclusion characterized by isolated thrombocytopenia with normal coagulation studies and absence of microangiopathic hemolytic anemia (MAHA). This patient presents with: - **Isolated severe thrombocytopenia** (8,000/μL) - **Normal coagulation parameters** (PT, aPTT, fibrinogen all normal) - **No schistocytes on smear** — rules out MAHA - **No systemic features** — no fever, renal dysfunction, or neurological symptoms - **Mucocutaneous bleeding** — typical of platelet dysfunction ### Differential Diagnosis Table | Feature | ITP | TTP | DIC | HUS | |---------|-----|-----|-----|-----| | Platelet count | Severe ↓ | Severe ↓ | Moderate ↓ | Moderate ↓ | | PT/aPTT | Normal | Normal | Prolonged | Normal | | Fibrinogen | Normal | Normal | Low | Normal | | Schistocytes | Absent | Present | Present | Present | | Fever | No | Yes (classic) | Variable | No | | Renal dysfunction | No | Yes (pentad) | Yes | Yes (defining) | | Neurological sx | No | Yes (pentad) | Variable | No | | Hemolysis | No | Yes (MAHA) | Yes | Yes (MAHA) | **High-Yield:** The **absence of schistocytes** is the single most important finding that excludes TTP and HUS in this case. ### Pathophysiology of ITP 1. Autoimmune destruction of platelets (anti-GPIIb/IIIa or anti-GPIb antibodies) 2. Reduced platelet survival in spleen and liver 3. Bone marrow shows normal or increased megakaryocytes (compensatory) 4. Coagulation cascade remains intact → normal PT, aPTT, fibrinogen **Clinical Pearl:** ITP typically presents with mucocutaneous bleeding (gums, epistaxis, petechiae) rather than deep tissue or visceral bleeding, which would suggest coagulation factor deficiency. ### Why Coagulation Studies Are Normal in ITP ITP is a **platelet number disorder**, not a coagulation factor disorder. The intrinsic, extrinsic, and common pathways are all intact: - PT (extrinsic pathway) → normal - aPTT (intrinsic pathway) → normal - Fibrinogen (final common pathway) → normal **Mnemonic: "ITP = Isolated Thrombocytopenia with Preserved coagulation"** ### Management Approach (Relevant Context) For symptomatic ITP with platelet count <30,000/μL: 1. First-line: Corticosteroids or IVIG 2. Second-line: Anti-D immunoglobulin (if Rh+) 3. Splenectomy if steroid-responsive 4. TPO receptor agonists (eltrombopag, romiplostim) for chronic ITP