ADHD comorbidity can matter when assessing cortical thickness abnormalities in patients with bipolar disorder

Abstract

Objectives Attention-deficit hyperactivity disorder (ADHD) is prevalent in patients with bipolar disorder (BP), but very few studies consider this when interpreting magnetic resonance imaging findings. No studies, to our knowledge, have screened for or controlled for the presence of ADHD when examining cortical thickness in patients with BP. We used a 2 × 2 design to evaluate the joint effects of BP and ADHD on cortical thickness and uncover the importance of ADHD comorbidity in BP subjects. Methods The study included 85 subjects: 31 healthy controls, 17 BP-only, 19 ADHD-only, and 18 BP/ADHD. All patients with BP were subtype I, were euthymic, and were not taking lithium. Groups did not differ significantly in age or sex distribution. We used cortical thickness measuring tools combined with cortical pattern matching methods to align sulcal/gyral anatomy across participants. Significance maps were used to check for both main effects of BP and ADHD and their interaction. Post-hoc comparisons assessed how the effects of BP on cortical thickness varied as a function of the presence or absence of ADHD. Results Interactions of BP and ADHD diagnoses were found in the left subgenual cingulate and right orbitofrontal cortex, demonstrating that the effect of BP on cortical thickness depends on ADHD status. Conclusions Some brain abnormalities attributed to BP may result from the presence of ADHD. Diagnostic interactions were found in regions previously implicated in the pathophysiology of BP, making it vital to control for an ADHD comorbid diagnosis when attempting to isolate neural or genetic abnormalities specific to BP.

Cortical thickness in bipolar disorder: a systematic review

“…Four whole‐brain and two ROI studies reported altered cortical thickness in the left anterior cingulate region [Brodmann's area (BA) 24 and/or BA 25]. Fornito et al.…”

“…Four whole-brain (34,37,40,45) and two ROI (42, 43) studies reported altered cortical thickness in the left anterior cingulate region [Brodmann's area (BA) 24 and/or BA 25]. Fornito et al (43) were the only group to report increased cortical thickness of the right subgenual anterior cingulate of the BD group compared to the HC group; this finding was specific to male patients only.…”

“…Another possibility suggested by the authors was that this finding might be related to a distinct neuroanatomical phenotype of BD with the onset of psychotic features. Six studies reported cortical thinning of the left paracingulate region (BA 32) [ROI: (42); wholebrain: (34,37,40,41,45)]. Six studies reported cortical thinning of the left superior temporal gyrus (BA 22) [ROI: (32,44); whole-brain: (31,34,37,41)].…”

“…Six studies reported cortical thinning of the left paracingulate region (BA 32) [ROI: (42); wholebrain: (34,37,40,41,45)]. Six studies reported cortical thinning of the left superior temporal gyrus (BA 22) [ROI: (32,44); whole-brain: (31,34,37,41)]. Some whole-brain studies also reported more widespread cortical thinning across the temporal lobes [including regions of the temporal pole (BA 38) (34, 37), middle temporal gyrus (BA 21) (34,37), and inferior temporal gyrus (BA 20) (34,37,41)].…”

“…Six studies reported cortical thinning of the left superior temporal gyrus (BA 22) [ROI: (32,44); whole-brain: (31,34,37,41)]. Some whole-brain studies also reported more widespread cortical thinning across the temporal lobes [including regions of the temporal pole (BA 38) (34, 37), middle temporal gyrus (BA 21) (34,37), and inferior temporal gyrus (BA 20) (34,37,41)]. Three studies reported on the cortical thickness of the parahippocampal gyrus (33,38,41).…”