A 71-year-old man with persistent leukopenia and thrombocytopenia was referred to the haematology department with a suspicion of a myelodysplastic neoplasm (MDS). Upon presentation, the patient was asymptomatic. Peripheral blood analysis confirmed leukopenia and thrombocytopenia. Furthermore, IgG was elevated, while IgM, total protein and the kappa-lambda free light chain (FLC) ratio were within normal ranges. Protein electrophoresis pattern showed a prominent monoclonal peak in the gamma globulin region. The monoclonal peak was identified as IgG heavy chain without corresponding kappa or lambda light chains by immunofixation analysis. Bone marrow cytology did not provide evidence for MDS; however, an increased plasmocytosis of 8% was detected. Immunophenotyping showed the presence of 6.6% CD19+, CD38++, CD138+, CD45+ and CD56- plasma cells without cytoplasmic light chain expression. The latter was confirmed by histologic review of the bone marrow biopsy using immunohistochemical staining. Immunoglobin gene rearrangement analysis was indicative for the presence of a monoclonal B-cell or plasma cell neoplasm. On positron emission tomography (PET)-scan only a mild splenomegaly was seen. Based on all these results, the diagnosis of a gamma heavy chain disease (gHCD) was made. As the patient was asymptomatic, treatment was not indicated. Blood count and health status were unchanged at a check-up six months later. Further follow-up is performed every six months. This case report presents the diagnostic work-up of a patient with gHCD. Laboratory analysis contributing to the diagnosis of gHCD included protein electrophoresis, immunofixation, bone marrow cytology, immunophenotyping, molecular analysis and pathological examinations of a bone biopsy.

(BELG J HEMATOL 2024;15(2):49–53)