Gamma heavy chain disease: cytological diagnosis of a rare lymphoid malignancy facilitated by correlation with key laboratory findings

The 2008 World Health Organization (WHO) Classification of Tumours of Haematopoietic and Lymphoid Tissues defines gamma heavy chain disease (gHCD) as a B-cell neoplasm that produces monoclonal gamma immunoglobulin (IgG) heavy chain without corresponding light chains. Since its original description in the 1960s, fewer than 200 cases have been reported. Patients may present with a myriad of constitutional symptoms and some have concomitant autoimmune disease, most notably rheumatoid arthritis. Because of the protean clinical presentation, the diagnosis of gHCD is often delayed and requires close collaboration between clinicians and pathologists, including both anatomical and clinical pathologists. We report a case of gHCD in which the definitive diagnosis was made by integrating the findings of fine needle aspiration (FNA) cytology, flow cytometry and serum protein electrophoresis (SPEP) and immunofixation results. To our knowledge, this is the first description of the cytological findings in gHCD. This case highlights the need for close collaboration between diverse subspecialty pathologists, including cytopathologists, haematopathologists and laboratory medicine practitioners, in establishing a specific diagnosis of a rare lymphoproliferative disorder on cytology. Case report