Localised pulmonary crystal-storing histiocytosis with underlying extranodal marginal zone lymphoma: A case report

Abstract

Crystal-storing histiocytosis (CSH) is a rare entity, composed of a proliferation of non-neoplastic histiocytes with an accumulation of intracytoplasmic crystalline material. It is often associated with an underlying lymphoproliferative disorder, most often those that express monoclonal immunoglobulins, such as multiple myeloma and lymphoplasmacytic lymphoma. Here we report a case of localised pulmonary CSH in an asymptomatic 54-year-old man, found to have an incidental solid lesion in the right lung on computed tomography (CT). The lesion was composed of sheets of CD68 positive histiocytes that contained refractile eosinophilic crystalline inclusions, scattered lymphoid follicles of CD20 positive B lymphocytes, and occasional plasma cells. PCR for immunoglobulin heavy chain gene rearrangement confirmed the presence of a monoclonal population of B cells. These findings were supportive of a diagnosis of CSH with an underlying B cell/ plasma cell lymphoproliferative disorder, which was favoured to be an extranodal marginal zone lymphoma after clinical and radiological workup. Recognition of this rare entity is important as it may obscure an underlying lymphoproliferative disorder. A diagnosis of CSH should prompt careful exclusion of neoplasia, including clinical workup for systemic disease. In this case report we also discuss clinical features and diagnostic pitfalls.