[Rapid development of primary amyloidosis after two years' follow-up of monoclonal gammopathy of undetermined significance (MGUS)].

Recently, we have encountered an unusual case of "monoclonal gammopathy of undetermined significance (MGUS)" in which some clinical features indicative of primary and amyloidosis (PA) were observed two years after the diagnosis of MGUS. The patient, born in 1925, was diagnosed of having MGUS (IgG-lambda type M-component level; 1 g/dl) in June 1990. The following clinical features occurred in close succession within five months after a stable course of two years: general malaise, abdominal, distension, pretibial edema and facial puffiness, ecchymoses on the chest wall, and dyspnea on effort. The biopsy specimens from the skin and gastric mucosa revealed amyloid deposition. The M-component levels in the serum and urine as well as the number of bone marrow plasma cells remained unchanged. The various kinds of laboratory examinations indicated that systemic amyloidosis rapidly developed within five months. It seems quite likely that the heart, liver, and spleen may be affected with amyloidosis. It is noteworthy that PA can occur without an increase in the serum M-component level at any time after the diagnosis of MGUS. An early diagnosis of PA as well as multiple myeloma should be kept in mind in the follow-up study of patients with MGUS.