To date, there are no reliable neurobiological or clinical markers that predict treatment outcome in patients with ADHD, reports a recent review from South Korea of treatment-refractory ADHD.
Stimulants such as methylphenidate (MPH) and non-stimulants such as atomoxetine are effective treatments of ADHD, but around 30% of patients do not respond to these medications; therefore, other psychostimulant and non-stimulant medications are needed. The high rates of multi-agent treatment in ADHD also suggest that suboptimal response to treatment is common. The ability to predict treatment-refractory ADHD would help to optimise treatment for patients with ADHD.
The authors stress that several clinical factors should be checked before ADHD is categorised as treatment-refractory; these include accuracy of diagnosis including recognition of comorbidities, appreciation of psychosocial factors, dose of ADHD treatment and adherence to medication.
The debate around pharmacogenetics, pharmacogenomics and neuroimaging studies and the ability to determine an association between response to medication for ADHD and genetic factors continues. Such studies are needed to help clinicians make better choices for their patients and determine appropriate drug use. Neurodevelopmental theories suggest that the dopaminergic, noradrenergic and catecholaminergic systems may be key in ADHD, and these are reviewed here, along with theories about the relationship between the side-effect profile of stimulant medications and various dopamine receptors and catechol-O-methyl-transferase (COMT).
The authors state that some neuroimaging studies have reported a relationship between treatment response and common patterns of brain structure/activity according to various genetic polymorphisms, and they review some studies of structural and functional neuroimaging.
Further studies of genetic and neuroimaging factors and their role in understanding the heterogeneity of ADHD are needed.
Shim SH, Yoon HJ, Bak J, et al. Clinical and neurobiological factors in the management of treatment refractory attention-deficit hyperactivity disorder. Prog Neuropsychopharmacol Biol Psychiatry 2016; 70: 237-244.