Serum
cardiac myosin light chain I (LCI) levels were quantitated using a radioimmunoassay kit in patients suspected of
dilated cardiomyopathy (DCM). In this study, 55 patients were evaluated between 1986 and 1991. They were composed of 40 males and 15 females, and their age was 27-75 years (51 +/- 11 years). The patients with renal dysfunction were excluded due to their serum
creatinine levels (greater than 2.0 mg/dl). 1) After cardiac catheterization, endomyocardial biopsy and echocardiography, 44 patients were diagnosed as DCM, 2 as
ischemic heart disease, 2 as chronic
myocarditis, 1 as
restrictive cardiomyopathy, 1 as dilated
hypertrophic cardiomyopathy, 1 as cardiac
amyloidosis, 2 as
myopathy, 1 as
polymyositis and 1 as
hypothyroidism. 2) Only two patients with DCM had elevated LCI. Besides, two patients with
myopathy or
hypothyroidism had elevated LCI. 3) In the follow-up, one patient died suddenly 6 months later and another showed normal value of LCI four years later. 4) LCI elevation in DCM was not related to either the severity of
heart failure or cardiac function and it showed no finding of 201Tl myocardial defect or elevated CPK. 5) The mechanism for elevated LCI in
myopathy is related to a cross-reaction with
myosin light chain in the skeletal muscle. In
hypothyroidism, it may be related to decreased clearance of normal LCI concentration or increased
myosin light chain from damaged skeletal muscle. In conclusion, it is evident that the measurement of LCI is not helpful in clinical assessment of patients with DCM, but may be useful in detection of
secondary cardiomyopathy.