A 79-year-old man manifested with constitutional symptoms and splenomegaly, 10 cm below the left costal margin. A complete blood count showed: mild anaemia (11.9 g/L), mild thrombocytopenia (141 x109/L) and lymphocytosis (white cell count 15.7×109/l, 82% lymphocytes). Biochemistry showed an increase in lactate dehydrogenase and beta-2-microglobulin and a monoclonal IgM lambda component (5g/L). Peripheral blood film showed (image 1) medium sized lymphocytes with round nucleus, condensed chromatin and nucleoli in some cells; the cytoplasm was moderately abundant, pale and irregular and contained elongated, fine, azurophilic inclusions with appearance of Auer rods. These inclusions were negative for myeloperoxidase by cytochemistry. Bone marrow aspirate (image 1) demonstrated infiltration by lymphocytes (44% of total cellularity) with the following phenotype (flow cytometry): CD19+, CD20+, CD22+, CD79b+, CD5-, CD10-, CD200-, CD23-, CD43-, CD38-, CD25-, CD103-, CD123-, CD11c heterogeneous. The karyotype was complex (46,XY,der(5)(5pter->5q33::13q14->13q34::5q34),der(13)(13pter->13q14::5q34->5qter),del(17)(p13p11)[9]/46,XY[11]) and fluorescence in situ hybridization confirmed TP53 deletion (55%) and 13q14.3 and 13q34 deletion (71%), both breakpoints were involved in the chr13 insertion to chr 5. A Next-Generation Sequencing Panel targeting 136 genes recurrently mutated in lymphoid neoplasms detected only a pathogenic TP53 mutation (p.Pro152AlafsTer14 with variant allele fraction of 51%). The bone marrow biopsy (image 2) showed an infiltration (30-40% of cellularity) by mature B lymphocytes (CD20+, CD79b+) with a predominantly intrasinusoidal pattern, positive for Bcl-2, IgM and IgD and negative for CD5, CD10, Cyclin- D1, CD25 and CD123 (Image 2). A diagnosis of splenic marginal lymphoma (SMZL) with adverse cytogenetic alterations was made.

Inclusions with appearance of Auer rods are unusual in non-myeloid neoplasm. These inclusions, unlike Auer rods, show negativity to myeloperoxidase and could correspond to protein crystals. In B-cell lymphoid neoplasms these structures are more frequently seen in plasma cell neoplasms while its presence is very exceptional in the remaining B-cell lymphoproliferative disorder. Some cases of chronic lymphocytic leukaemia have been described but rarely in SMZL. In these cases, a comprehensive evaluation of all techniques is essential. Our case highlights the importance of an integrated diagnosis with morphological, histopathological, immunophenotypic, cytogenetic and molecular biology findings.