A Case of Isaacs Syndrome Developed After Thymectomy for Myasthenia Gravis

A 54-year-old man was referred to our hospital due to calf pain and gait disturbance. Two years earlier, he had developed ptosis of the left eye. A routine health check conducted two years later revealed a thymoma with positive anti-acetylcholine receptor antibodies. He was diagnosed with myasthenia gravis and underwent thymectomy. Eight days after the surgery, he experienced involuntary calf muscle movements and pain, leading to worsening gait disturbance. Upon admission, he presented with cold toes, ptosis of the left eye, and continuous myokymia of both legs, which persisted during sleep. Laboratory tests revealed the presence of anti-contactin-associated protein 2 (anti-CASPR2) and anti-leucine-rich glioma-inactivated protein 1 (anti-LGI1) antibodies in the serum, along with myokymic discharges observed in electromyography. A diagnosis of Isaacs syndrome was made. The patient was treated with plasmapheresis and methylprednisolone pulse therapy, followed by intravenous immunoglobulin therapy, leading to the resolution of his symptoms. To our knowledge, this is the first reported case of Isaacs syndrome developing soon after thymectomy.