Improved Odor Sensitivity in Attention-Deficit/Hyperactivity Disorder

Background: Deficits in olfactory function are common features in neurodegenerative and neuropsychiatric disorders. In Parkinson's disease, olfactory deficits were found in up to 90% of patients, and there is evidence for dopaminergic dysfunction underlying these deficits. Because of the involvement of the dopamine system in the pathophysiology of attention-deficit/hyperactivity disorder (ADHD), olfactory function was investigated in children with the disorder. Methods: We assessed odor threshold, identification, and discrimination in 20 children and adolescents with ADHD without medication, 20 patients with ADHD treated with methylphenidate, and 20 healthy control subjects matched for IQ, age, and sex. Results: Odor sensitivity was higher (lower threshold) in ADHD patients without medication than in healthy control subjects (p <.004; Cohen's d = 1.273), whereas medicated patients did not differ significantly from healthy control subjects. No significant differences between groups with regard to odor discrimination or identification were detected. Conclusions: Selectively improved odor sensitivity in children with ADHD is reported for the first time, whereas odor discrimination and identification were unaffected. Stimulant medication normalized the odor sensitivity threshold. It is proposed that dopaminergic dysregulation is involved in this phenomenon.