Rasmussen encephalitis: Predisposing factors and their potential role in unilaterality

Objective Rasmussen encephalitis (RE) is a progressive and destructive inflammatory disease of one hemisphere. Its cause is unknown. We investigated comorbidity and laterality factors that might predispose to RE. Methods We retrospectively compared the histories of 160 RE patients to those with genetic generalized epilepsy (n = 154) and those with focal cortical dysplasia Type II (FCD II; n = 148). Results The median/mean age at symptom onset in RE was 7/10 years (range = 1–53 years), and 58.1% of the patients were female. The female sex predominated in RE patients, with age > 7 years at disease manifestation. The left hemisphere was affected in 65.6%. Perinatal complications (preterm birth, twin pregnancies, early acquired brain lesions) were more frequent in RE than in control patients. Ipsilateral facial autoimmune conditions (scleroderma en coup de sabre, uveitis, or chorioretinitis) were only observed in RE patients (6.9%). Onset of RE was more frequently associated with fever than that of FCD II. In 33.1% of RE patients, ≥1 potential risk factor was found. Interestingly, 11.9% of patients had one‐sided early brain lesions or facial autoimmune lesions ipsilateral to subsequent RE; none had such a lesion contralaterally. Significance Perinatal complications and facial autoimmune conditions may act as predisposing factors for RE. Fever might trigger RE manifestation. Further genetic or infectious contributors may be identified in the future. Single or combined hits may be required to elicit or facilitate the start of the disease. Ipsilateral early comorbid lesions or facial autoimmune processes might in part explain the enigmatic unilaterality of RE.