A ten year longitudinal examination of the incidence rate and age of childhood encephalopathy diagnoses in an autism spectrum disorder diagnosed cohort.

Autism spectrum disorder (ASD) is defined by persistent deficits in social communication/interaction and stereotypic behaviors with many diagnosed persons experiencing a developmental regression at >1 year‑old. It was hypothesized that progressive childhood encephalopathy is an important etiological factor in ASD pathogenesis. This hypothesis‑testing study examined the relationship between diagnosed childhood encephalopathy and ASD. The Independent Healthcare Research Database is composed of de‑identified linked eligibility and claim healthcare records prospectively generated from the Florida Medicaid system. A cohort of 101,736 persons eligible for Florida Medicaid from 1990‑2009 and continuously eligible with ≥10 outpatient office visits during the 120 month period following birth were examined using SAS software. There were 1,397 persons (7,223 person‑years) in the ASD diagnosed cohort and 100,339 persons (980,786 person‑years) in the undiagnosed cohort. The incidence rate of encephalopathy was examined using Cox proportional hazards ratio models. In the ASD cohort relative to the undiagnosed cohort, a significantly increased incidence rate of diagnosed encephalopathy was observed in the unadjusted and adjusted models. The risk for an encephalopathy diagnosed at >1 year‑old was greater than for an encephalopathy diagnosed at <1 year‑old. This study provides important new evidence supporting the hypothesis that a significant number of children with an eventual ASD diagnosis experience a progressive childhood en cephalopathy diagnosed at >1 year‑old.