“…[2] M-protein-related disease caused by pathological immunoglobulins and light chains, such as cryoglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome, AL amyloidosis, and light-chain deposition disease, can have diverse symptoms such as pyrexia, arthralgia, skin rash, peripheral neuropathy, thrombosis, and renal involvement, which mimic systemic rheumatic diseases. [3] Although M-protein-related diseases can cause fulminant end-organ damage, [4,5] indications for aggressive treatment of MGUS causing M-protein-related disease have not been known. We report a case of crystalglobulinemia, which is a rare form of M-protein-related disease, characterized by irreversible cryoprecipitation, and it is caused by monoclonal gammopathy that was previously diagnosed as MGUS.…”