Prevalence, clinical profiles, and prognosis of Isaacs syndrome: A nationwide survey study in Japan.

OBJECTIVES

To elucidate current epidemiological, clinical, and immunological profiles, and the treatment of Isaacs syndrome in Japan.

METHODS

We conducted a nationwide survey using established methods. Questionnaires were sent to neurological facilities throughout Japan to identify Isaacs syndrome patients seen between April 2018 and March 2021.

RESULTS

The estimated total number of Isaacs syndrome patients was 114 (95 % confidence interval [CI]: 89.63-138.91), and the estimated prevalence was 0.091 per 100,000 population. Detailed clinical data were available for 44 patients. The median age at onset was 40 (range, 17-78 years), and 55 % were female. The median time from symptom onset to diagnosis was 24 months (range, 1-372 months). Electrodiagnostic studies showed evidence of nerve hyperexcitability in 90 % (myokymic discharges in 50 % and stimulus-induced repetitive discharges in 32 %). Of the 28 patients examined in the cell-based assay, 22 % tested positive (11 % for both leucine-rich glioma-inactivated 1 [LGI1] and contactin-associated protein-like 2 [CASPR2] antibodies and 11 % for LGI1 antibodies only). The median modified Rankin Scale (mRS) score was 2 at diagnosis and 1.5 at the last visit. A high mRS score (mRS ≥4) at baseline was an independent risk factor for poor outcomes (mRS ≥3) (Odds ratio, 20.7; 95 % CI, 2.90-209.18; p < 0.001).

CONCLUSION

We elucidated the current epidemiological and clinical characteristics of Isaacs syndrome in Japan. Isaacs syndrome is a rare neuromuscular disorder. Electrophysiologic abnormalities were frequent, and serum antibodies were not detectable in the majority of patients. A high mRS score before treatment was a risk factor for poor outcomes.