Abstract
OBJECTIVE: We evaluated the stability of attention-deficit/hyperactivity (ADHD) symptoms from the toddler (24 months of age) to the preschool period (36-64 months of age) in a sample enriched for varied neurodevelopmental risk to ensure a range of ADHD symptoms. METHOD: Participants (n = 256) included infants with a family history of ADHD (n = 66), autism (n = 115), or neither (n = 75) who were prospectively followed over the first several years of life. At 24 and 36-64 months of age, parents completed the Preschool ADHD Rating Scale. At the preschool visit, children were classified into one of three mutually exclusive outcome groups: ADHD Concerns (i.e. elevated symptoms, clinician concern), Autism, or Comparison. ADHD symptom stability from the toddler to the preschool period was assessed, along with variability in early symptoms and change over time by preschool clinical presentation. RESULTS: Symptoms were moderately stable, with summary score correlations of 0.56-0.60. Total scores were significantly higher at 24 months among those with later concerns for ADHD or diagnoses of autism, and increased in these two groups over time, but decreased in the Comparison group. CONCLUSIONS: Symptom measurement at age 2 may be useful for identifying toddlers at higher risk for later behavioral challenges, with implications for early screening. Future work in this area can help delineate boundaries of developmental typicality versus atypicality, evaluate the specificity of early symptom elevations to longer-term outcomes, and identify patterns of symptom stability from the toddler period over time that may aid in identifying children at greatest risk for persistent/increasing challenges.