Creatine kinase (CK)-linked IgA in Isaacs' syndrome. An immune complex disease?

Electrophoresis of serum from a patient with Isaacs' syndrome revealed an atypical creatine kinase (CK) isoenzyme pattern which contained an extra band migrating between CK2(MB) and CK3(MM). Immunofixation demonstrated that the extra band was a complex of CK3(MM) and IgA. The presence of this complex seemed to correlate with increased serum CK levels which were associated with the aggravation of symptoms. Immunofluorescence studies on muscle biopsy samples revealed the presence of the complex in the muscle fiber membrane and motor endplate. The existence of CK-linked IgA in an Isaacs' syndrome suggests that an immunological abnormality may play a role in the pathological process of this rare syndrome.