MYOM2 and Miyoshi myopathy: Nonsecretory MM lacks an identifiable M-protein, while oligosecretory MM is defined by M-protein levels below the electrophoretic detection threshold of less than 1 g/L but with an abnormal involved SFLC concentration or ratio.18 The presence of polyclonal κ SFLCs complicated the initial diagnosis of κ light chain MM because no definitive M-protein could be identified.