Regressive autism with autoimmune encephalitis: case report and literature review of subtype of autism spectrum disorder

About one-third of individuals with autism spectrum disorder (ASD) show a sudden loss of acquired skills between the 2nd or 3rd years of life. The primary areas of loss were grouped into language skills, social interest, adaptive functioning, and motor skills. A 4-year and 2-month-old boy presented to the child and adolescent mental health and disease outpatient clinic with his parents with complaints of decreased eye contact, and regression in speech. His developmental milestones were within the typical range of three years and two months. During the investigation into the organic etiology of regression, serum anti-CASPR2 positivity was detected, and intravenous immunoglobulin administration was initiated. After 6 months of treatment and special education, there was a slight decrease in the CARS score along with improvements in adaptation to change, visual response, and non-verbal communication. This rare case of regressive autism accompanied by autoimmune encephalitis provides further evidence in the field that autoimmune encephalitis may influence the development of the regressive subtype of ASD. Differential diagnosis is crucial because additional immunotherapy may be beneficial in these cases. Further investigation is needed to identify the relationship.