A 52-year-old man with a history of rheumatoid arthritis presents with progressive bleeding gums, spontaneous bruising, and a 2-week history of melena. He has been on methotrexate and NSAIDs for the past 6 months. On examination, he is pale, with petechiae over his lower limbs and hepatosplenomegaly. Laboratory results show: Hemoglobin 8.2 g/dL, WBC 3,200/μL, Platelet count 45,000/μL, PT 16 s (prolonged), aPTT 48 s (prolonged), Fibrinogen 180 mg/dL (low), D-dimer elevated. Bone marrow biopsy shows hypocellular marrow with reduced megakaryocytes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Methotrexate-Induced Bone Marrow Suppression with Secondary DIC ### Key Clinical Features **Key Point:** Methotrexate (MTX), a folate antagonist used in rheumatoid arthritis, is a well-recognized cause of bone marrow suppression (pancytopenia), particularly at higher doses or with concurrent NSAID use (which reduces MTX renal clearance and raises plasma levels). Severe marrow failure can trigger secondary DIC. This patient presents with: - **6-month history of methotrexate + NSAIDs** — NSAIDs competitively inhibit renal tubular secretion of MTX, dramatically increasing MTX toxicity risk - **Pancytopenia (Hb 8.2, WBC 3,200, Platelets 45,000)** — classic triad of MTX-induced marrow suppression - **Hypocellular bone marrow with reduced megakaryocytes** — direct evidence of marrow suppression (not immune destruction, which would show normal/increased megakaryocytes) - **Prolonged PT + aPTT, low fibrinogen (180 mg/dL), elevated D-dimer** — secondary DIC triggered by marrow failure and systemic stress - **Hepatosplenomegaly** — consistent with MTX-induced hepatotoxicity and extramedullary hematopoiesis - **Mucosal bleeding + melena + petechiae** — consequence of thrombocytopenia and coagulopathy ### Why NOT Sepsis-Induced DIC (Option C) **Clinical Pearl:** The stem contains **no fever, no documented infection, no positive blood cultures, and no clinical signs of sepsis**. Attributing DIC to sepsis without any infectious trigger in the vignette is clinically unjustified. The entire clinical picture — drug history, pancytopenia, hypocellular marrow — points to a drug-induced etiology. ### Why NOT ITP (Option A) - ITP is characterized by **isolated thrombocytopenia** with **normal PT, aPTT, and fibrinogen** - ITP bone marrow shows **increased or normal megakaryocytes** (immune destruction of platelets, not reduced production) - This patient has pancytopenia + coagulopathy — incompatible with ITP ### Why NOT Evans Syndrome (Option D) - Evans syndrome = autoimmune hemolytic anemia + ITP; it does **not** cause prolonged PT/aPTT, low fibrinogen, or hypocellular marrow - The coagulation profile and marrow findings rule this out ### Pathophysiology ``` Methotrexate + NSAIDs ↓ (NSAIDs ↓ renal MTX clearance → ↑ MTX levels) Folate antagonism → DNA synthesis inhibition ↓ Bone marrow suppression (hypocellular marrow, ↓ megakaryocytes) ↓ Pancytopenia → systemic stress → coagulation cascade activation ↓ Secondary DIC: ↑PT/aPTT, ↓fibrinogen, ↑D-dimer ``` ### Management 1. **Immediately discontinue methotrexate and NSAIDs** 2. **Leucovorin (folinic acid) rescue** — to bypass MTX-induced folate blockade 3. **Supportive care** — platelet transfusion, FFP/cryoprecipitate for active bleeding 4. **Monitor** — CBC, LFTs, renal function, coagulation parameters 5. **Treat secondary DIC** — address underlying cause (MTX toxicity) [cite: KD Tripathi Essentials of Medical Pharmacology 8e, Ch 13; Harrison's Principles of Internal Medicine 21e, Ch 140]