Charcot‐Leyden crystals in the trephine biopsy of a patient with a <i>FIP1L1‐PDGFRA</i>– positive myeloproliferative disorder

Abstract

A 55-year-old male was referred to the haematology clinic for investigation of an abnormal full-blood count and splenomegaly. The full-blood count showed haemoglobin 137 g/l, white cell count 53·2 × 109 /l and platelets 42 × 109/l. The blood film showed neutrophilia with a left-shifted myeloid series. A marked eosinophilia (eosinophil count 16·5 × 109 /l) was also present. An ultrasound examination confirmed that the spleen was enlarged, measuring 16·3 cm × 10·8 cm × 14 cm. The patient was investigated for a suspected myeloproliferative disorder. A bone marrow aspirate showed increased myelopoiesis. Cytogenetic analysis showed a normal karyotype. Testing for BCR-ABL by fluorescence in situ hybridisation was negative. The trephine biopsy, stained with haematoxylin and eosin (top) and Giemsa (bottom), showed a hypercellular marrow, with marked granulocytic hyperplasia especially involving the eosinophilic component and reticulin fibrosis (grade 2/4), features consistent with a myeloproliferative disorder. Charcot-Leyden crystals (arrows) were seen in the areas with the highest concentrations of eosinophils. Molecular analysis of peripheral blood demonstrated that the FIP1L1–PDGFRA fusion gene was present. Charcot-Leyden crystals are a rare finding in bone marrow biopsies. They are composed of lysophospholipase, a constituent protein of eosinophils and are formed when increased turnover of eosinophils occurs. They have been described in association with both reactive and clonal causes of an eosinophilia. When present, they are usually visible on haematoxylin and eosin-stained sections, but are more readily seen with a Giemsa stain. The patient was treated with imatinib, which resulted in normalisation of the full-blood count.