Effects of medication on neuroimaging findings in bipolar disorder: an updated review.
OBJECTIVE
Neuroimaging is an important tool for better understanding the neurobiological underpinnings of bipolar disorder (BD). However, potential study participants are often receiving psychotropic medications which can possibly confound imaging data. To better interpret the results of neuroimaging studies in BD, it is important to understand the impact of medications on structural magnetic resonance imaging (sMRI), functional MRI (fMRI), and diffusion tensor imaging (DTI).


METHODS
To better understand the impact of medications on imaging data, we conducted a literature review and searched MEDLINE for papers that included the key words bipolar disorder and fMRI, sMRI, or DTI. The search was limited to papers that assessed medication effects and had not been included in a previous review by Phillips et al. (Medication effects in neuroimaging studies of bipolar disorder. Am J Psychiatry 2008; 165: 313-320). This search yielded 74 sMRI studies, 46 fMRI studies, and 15 DTI studies.


RESULTS
Medication appeared to influence many sMRI studies, but had limited impact on fMRI and DTI findings. From the structural studies, the most robust finding (20/45 studies) was that lithium was associated with increased volumes in areas important for mood regulation, while antipsychotic agents and anticonvulsants were generally not. Regarding secondary analysis of the medication effects of fMRI and DTI studies, few showed significant effects of medication, although rigorous analyses were typically not possible when the majority of subjects were medicated. Medication effects were more frequently observed in longitudinal studies designed to assess the impact of particular medications on the blood oxygen level-dependent (BOLD) signal. With a few exceptions, the observed effects were normalizing, meaning that the medicated individuals with BD were more similar than their unmedicated counterparts to healthy subjects.


CONCLUSIONS
The effects of psychotropic medications, when present, are predominantly normalizing and thus do not seem to provide an alternative explanation for differences in volume, white matter tracts, or BOLD signal between BD participants and healthy subjects. However, the normalizing effects of medication could obfuscate differences between BD and healthy subjects, and thus might lead to type II errors.
Department of Psychiatry, Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA. hafemand@upmc.edu
Danella M
DM
Hafeman
Kiki D
KD
Chang
Amy S
AS
Garrett
Erica M
EM
Sanders
Mary L
ML
Phillips
D000927:Anticonvulsants / Q000494:pharmacology*; D018692:Antimanic Agents / Q000494:pharmacology*; D014150:Antipsychotic Agents / Q000494:pharmacology*; D001714:Bipolar Disorder / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D001921:Brain / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D056324:Diffusion Tensor Imaging; D059907:Functional Neuroimaging; D006801:Humans; D018020:Lithium Compounds / Q000494:pharmacology*; D008279:Magnetic Resonance Imaging
D000927:Anticonvulsants; D018692:Antimanic Agents; D014150:Antipsychotic Agents; D018020:Lithium Compounds