Case reportIsaacs syndrome with CASPR2 antibody: A series of three cases

- We reported three CASPR2 antibody positive patients with Isaacs syndrome.
- Corticosteroids, DFPP and rituximab were showed to be effective in treatment.
- The titer of serum CASPR2-Ab changed in parallel with their improvement of symptoms.
- Patients with or without neoplasm showed some different clinical characteristics.

Isaacs syndrome is a form of peripheral nerve hyperexcitability, characterized by spontaneous muscle twitching and stiffness. Some patients are reported to be positive for CASPR2 antibody that may be one of the pathogenic autoantibodies in Isaacs syndrome. We reported a series of three patients with Isaacs syndrome, including their clinical features, electrophysiologic findings, laboratory parameters and therapeutic responses. All the three patients were positive for CASPR2 antibodies examined on transfected human embryonic kidney 293 cells by indirect immunofluorescence method. One patient had invasive thymoma. Symptomatic treatment was not sufficient for them, while immunotherapies including corticosteroids, double filtration plasmapheresis and rituximab provided favorable outcomes. The titers of CASPR2 antibody decreased after immune modulating therapy in parallel to clinical improvements in two patients.