Creatine phosphokinase-linked immunoglobulin associated with hypokalemic myopathy

We present three women with hypokalemic myopathy in whom serum creatine phosphokinase (CPK) was bound to serum immunoglobulin (macro-CPK). In all three cases, CPK isozyme electrophoresis demonstrated an extra CPK band between CPK-MM and CPK-MB. The bound immunoglobulins were identified as IgA/A-kappa and lambda, IgA-lambda and IgA-kappa and lambda, respectively. In all cases, histological examination of the biopsied muscles revealed necrotic and/or regenerating fibers. In each patient, potassium replacement therapy returned the macro-CPK as well as the marked elevations of serum muscle enzymes to normal. Taken together with other recent reports, our findings suggested that CPK-immunoglobulin binding may be related to the emergence of pathophysiology of hypokalemic myopathy.