A 35-year-old woman presents with a 2-year history of easy bruising, epistaxis, and menorrhagia. Platelet count is 18,000/μL with normal coagulation studies and blood film showing no schistocytes. What is the most common cause of this clinical presentation?

Explanation

## Diagnosis: Immune Thrombocytopenia (ITP) ### Clinical Presentation Analysis The patient presents with: - Severe thrombocytopenia (18,000/μL) - Mucocutaneous bleeding (epistaxis, menorrhagia, bruising) - **Normal coagulation studies** (PT, aPTT normal) - **Absence of schistocytes** on blood film - Chronic course (2-year history) ### Why ITP is the Most Common Cause **Key Point:** ITP is the most common cause of isolated thrombocytopenia in otherwise healthy individuals, accounting for 60–80% of cases presenting with platelet counts <20,000/μL and no systemic features. ### Differential Diagnosis of Severe Thrombocytopenia | Feature | ITP | TTP | DIC | Drug-Induced | |---------|-----|-----|-----|---------------| | Platelet count | <20,000 common | <20,000 | <20,000 | Variable | | Coagulation studies | **Normal** | **Normal** | **Prolonged** | Normal | | Schistocytes | Absent | **Present** | **Present** | Absent | | LDH | Normal/mild ↑ | **Markedly ↑** | **Markedly ↑** | Normal | | Renal function | Normal | **Impaired** | **Impaired** | Normal | | Fever/CNS symptoms | Absent | **Present** | Variable | Absent | | Duration | Chronic | Acute | Acute | Acute | **Clinical Pearl:** The **absence of schistocytes and normal coagulation studies** rule out TTP and DIC. The **chronic 2-year course** rules out acute drug-induced or DIC. ITP remains the diagnosis of exclusion. ### Pathophysiology of ITP **High-Yield:** ITP is an autoimmune disorder where: 1. Autoantibodies (anti-GPIIb/IIIa, anti-GPIb/IX) bind platelet surface antigens 2. Antibody-coated platelets are destroyed in the spleen and liver (reticuloendothelial clearance) 3. Bone marrow shows **normal or increased megakaryocytes** (compensatory response) 4. Result: isolated thrombocytopenia with normal RBC and WBC ### Diagnostic Criteria for ITP **Key Point:** ITP is diagnosed by: - Thrombocytopenia (<150,000/μL) - Absence of other causes (normal coagulation, no schistocytes, no splenomegaly, no lymphadenopathy) - No secondary causes (drugs, autoimmune disease, infection) - Bone marrow examination shows normal/increased megakaryocytes (not routinely needed if clinical picture is clear) ### Epidemiology **Mnemonic: ITP Prevalence — "CHRONIC WOMEN"** - **C**hronic form: 80% of adult cases - **H**igher in women (2:1 female:male ratio) - **R**are in children (acute form more common) - **O**ften asymptomatic at diagnosis - **N**o systemic features - **I**solated thrombocytopenia - **C**omplete recovery possible with treatment --- ## Why Each Distractor is Wrong **Thrombotic thrombocytopenic purpura (TTP):** While TTP presents with severe thrombocytopenia, it is characterized by **schistocytes on blood film, markedly elevated LDH, acute renal dysfunction, fever, and CNS symptoms** (pentad). This patient has **normal coagulation studies, no schistocytes, and a chronic course**, excluding TTP. **Disseminated intravascular coagulation (DIC):** DIC causes thrombocytopenia but is accompanied by **prolonged PT/aPTT, elevated D-dimer, low fibrinogen, and schistocytes**. This patient has **normal coagulation studies**, which excludes DIC. DIC is also an acute process, not chronic. **Drug-induced thrombocytopenia:** While possible, drug-induced thrombocytopenia is less common than ITP and typically resolves within days to weeks of drug discontinuation. The **2-year chronic course** without mention of causative drugs makes ITP far more likely. Additionally, drug-induced thrombocytopenia would require a clear temporal relationship to a known offending agent.