(BMJ)—A woman in her 70s with seronegative RA and monoclonal gammopathy of undetermined significance (MGUS) presented with a 13-year hx of hand nodules that were occasionally tender and inflamed. Prior aspiration was negative for crystals, positive for inflammatory cells, without a specific dx. Histology confirmed the dx. What is it?
Nodular scleroderma
Tophaceous pseudogout
Fibroblastic rheumatism
Crystal-storing histiocytosis
Rheumatoid nodules
You are correct. Histology showed a subdermal necrotic mass with neutrophils surrounding crystal-like hyaline bodies; periodic acid Schiff was positive and Congo red was negative, consistent with crystal-storing histiocytosis associated with the patient’s MGUS. Such hand nodules are typically seen with seropositive RA, but this patient was seronegative for the disease. Crystal-storing histiocytosis is a rare manifestation of MGUS, multiple myeloma, and some types of lymphoma; it can affect the kidneys, lungs, bone marrow, lymph nodes, liver, spleen, and GI tract.

BMJ 2021;372:m4969