Isaacs' Syndrome Associated With Acetylcholine Receptor Antibodies Developed After Removal of Malignant Thymoma

ABSTRACT

Isaacs' syndrome is a rare and heterogeneous syndrome of continuous muscle fiber activity that originates from peripheral nerves. We report a 56-year-old male patient who showed symptoms of Isaacs' syndrome after the removal of a malignant thymoma. Needle electromyography revealed spontaneously occurring repetitive myokymic discharge in the affected muscles. Acetylcholine receptor (AChR) antibodies were significantly elevated, but clinical and electrophysiologic findings did not indicate the presence of myasthenia gravis. We deduce that in Isaacs' syndrome, raised AChR antibodies may facilitate rather than inhibit cholinergic action.