Systemic mast cell disease presenting with peripheral blood eosinophilia

Patients with mast cell disease most frequently present with skin lesions (urticaria pigmentosa), with systemic involvement in many cases. However, a small subset of patients with systemic mast cell disease lacks skin lesions and, in these patients the correct diagnosis may be difficult to establish. Patients with systemic mast cell disease commonly have hematologic abnormalities, including eosinophilia in up to 20% of cases, but isolated eosinophilia has been reported rarely. We describe an 82-year-old woman who was admitted to Rhode Island Hospital for coronary artery disease and unstable angina. Incidentally, an absolute eosinophil count of 7.84 × 10⁹/L (normal, <0.45 × 10⁹/L) was detected with moderate thrombocytopenia and mild anemia. Review of earlier records revealed that absolute eosinophilia had been present for approximately 4 months, initially without other hematologic abnormalities. Clinical work-up showed left upper quadrant tenderness. No skin lesions were identified. Bone marrow core biopsy revealed paratrabecular, perivascular, and medullary mast cell aggregates with eosinophils, suggestive of mast cell disease. At autopsy the diagnosis was confirmed. Mast cell aggregates were found in the liver, spleen, lymph nodes, and bone marrow, and chloroacetate esterase stain highlighted mast cell granules. The bone marrow was also hypercellular with granulocytic and eosinophilic hyperplasia, suggestive of a poorly defined myeloproliferative disorder. Patients with systemic mast cell disease initially may present with peripheral eosinophilia. Clinical suspicion of the diagnosis facilitates proper handling of the bone marrow core biopsy specimen to allow the demonstration of mast cell granules.