MPN-499: Unveiling Essential Thrombocythemia: A Case of CALR-Driven Thrombocytosis and Targeted Therapy

Essential thrombocythemia (ET) is a chronic myeloproliferative neoplasm characterized by excessive platelet production, leading to increased risks of thrombotic and hemorrhagic complications. The identification of CALR mutations in JAK2 -negative cases has become pivotal for accurate diagnosis and guiding therapeutic strategies. Early recognition and tailored treatment are essential to mitigate complications and improve patient outcomes. A female patient presented with a 2-week history of fatigue, generalized weakness, nasal congestion, and flu-like symptoms, initially treated symptomatically by her family physician. Due to persistent symptoms, a hemogram was performed, revealing a significantly elevated platelet count (PLT: 2,788 × 10 3 /mm 3 ). Following referral to a hematology specialist, a repeat hemogram confirmed thrombocytosis (PLT: 2,925 × 10 3 /mm 3 ). Clinical examination noted pale skin, mucosal bleeding in the oral cavity, and subcutaneous hemorrhages. Laboratory tests, including a peripheral blood smear, showed numerous aggregated platelets with normochromic, normocytic erythrocytes. Molecular analysis identified a CALR mutation (exon 9, insertion type 2, 5 bp), with negative JAK2 V617F and MPL mutations, confirming the diagnosis of ET (ICD-10: D47.3). The patient was admitted for comprehensive evaluation and treatment. Chest x-ray showed bilateral bronchovascular accentuation, and abdominal ultrasound revealed mild splenomegaly (spleen diameter: 11 cm), consistent with ET. Hemostasis tests indicated a slightly prolonged activated partial thromboplastin time (37″) and normal D-dimer (110 μg/L). Treatment included peginterferon alfa-2a (weekly), cytoreductive therapy with hydroxyurea, Fraxiparine (nadroparin) for thrombotic prophylaxis, allopurinol, proton pump inhibitors, and intravenous fluids for supportive care. Post treatment, platelet counts significantly decreased to 660 × 10 3 /mm 3 , with notable improvement in fatigue and weakness. This case underscores the critical role of molecular diagnostics in confirming CALR -positive ET and the effectiveness of combined cytoreductive and supportive therapies in managing thrombocytosis and associated symptoms. Prompt diagnosis and individualized treatment are vital to reducing the risk of complications and improving quality of life in ET patients.