[IgM-lambda type monoclonal gammopathy of undetermined significance showing non-specific anti-streptolysin O activity...

We report a case of IgM-lambda type monoclonal gammopathy of undetermined significance showing non-specific anti-streptolysin O activity of extremely high level. An 83-year-old man developed high grade fever, cough and sputum. He was admitted to our hospital under a diagnosis of acute pneumonia by chest X-ray. He showed anti-streptolysin O (ASO) activity in extremely high level measured by a latex immunoaggregation method (LA-method). Although antibiotics cured the acute pneumonia, the ASO activity had remained in high level. Serum protein electrophoresis disclosed existence of M-protein and the M-protein was found to be IgM, lambda class by immunoelectrophoresis. The ASO activity measured by the LA method was ascribed to the M-protein because the level of M-component shown by the electrophoresis was decreased by absorption of the serum with streptolysin O-coated latex beads that were used in the LA-method. However, ASO activity measured by Rantzs-Randall method was in normal level. The ASO activity measured by the LA-method was absorbed with bovine serum albumin coated latex beads without streptolysin O. Therefore, it was concluded that the M-protein was not reacted with streptplysin O itself but was reacted with bovine serum albumin coated latex beads. The ASO activity of extremely high level in our case was non-specific reaction caused by the M-protein.