High IQ May “Mask” the Diagnosis of ADHD by Compensating for Deficits in Executive Functions in Treatment-Naïve Adults With ADHD

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Abstract
Objective: To evaluate and compare the performance of adults with ADHD with high and standard IQ in executive functions (EF) tasks. Method: We investigated the neuropsychological performance of 51 adults with ADHD, compared with 33 healthy controls (HC) while performing a wide battery of neuropsychological tests that measure executive functioning. Adults with clinical diagnosis of ADHD were divided into two groups according to their IQ level (IQ ≥ 110—ADHD group with more elevated IQ, and IQ < 110—ADHD group with standard IQ). Results: The ADHD group with standard IQ presented a worse executive functioning compared with the HC group in the following measures: Stroop 2 (p = .000) and 3 (p = .000), Trail Making Test (TMT) B (p = .005), Wisconsin Card-Sorting Test (WCST)—perseverative errors (p = .022) and failures to maintain set (p = .020), Continuous Performance Test (CPT)—omission errors (p = .005) and commission errors (p = .000), and Frontal Assessment Battery (FAB)—conceptualization (p = .016). The ADHD group with more elevated IQ presented only impairments in the CPT—commission errors (p = .019) when compared with the control group. Conclusion: Adults with ADHD and more elevated IQ show less evidence of executive functioning deficits compared with those with ADHD and standard IQ, suggesting that a higher degree of intellectual efficiency may compensate deficits in executive functions, leading to problems in establishing a precise clinical diagnosis.

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