Right orbitofrontal corticolimbic and left corticocortical white matter connectivity differentiate bipolar and unipolar depression.
OBJECTIVE
The absence of pathophysiologically relevant diagnostic markers of bipolar disorder (BD) leads to its frequent misdiagnosis as unipolar depression (UD). We aimed to determine whether whole brain white matter connectivity differentiated BD from UD depression.


METHODS
We employed a three-way analysis of covariance, covarying for age, to examine whole brain fractional anisotropy (FA), and corresponding longitudinal and radial diffusivity, in currently depressed adults: 15 with BD-type I (mean age 36.3 years, SD 12.0 years), 16 with recurrent UD (mean age 32.3 years, SD 10.0 years), and 24 healthy control adults (HC) (mean age 29.5 years, SD 9.43 years). Depressed groups did not differ in depression severity, age of illness onset, and illness duration.


RESULTS
There was a main effect of group in left superior and inferior longitudinal fasciculi (SLF and ILF) (all F > or = 9.8; p < or = .05, corrected). Whole brain post hoc analyses (all t > or = 4.2; p < or = .05, corrected) revealed decreased FA in left SLF in BD, versus UD adults in inferior temporal cortex and, versus HC, in primary sensory cortex (associated with increased radial and decreased longitudinal diffusivity, respectively); and decreased FA in left ILF in UD adults versus HC. A main effect of group in right uncinate fasciculus (in orbitofrontal cortex) just failed to meet significance in all participants but was present in women. Post hoc analyses revealed decreased right uncinate fasciculus FA in all and in women, BD versus HC.


CONCLUSIONS
White matter FA in left occipitotemporal and primary sensory regions supporting visuospatial and sensory processing differentiates BD from UD depression. Abnormally reduced FA in right fronto-temporal regions supporting mood regulation, might underlie predisposition to depression in BD. These measures might help differentiate pathophysiologic processes of BD versus UD depression.
Versace
Amelia
A
Department of Psychiatry, University of Pittsburgh School of Medicine, Pennsylvania, USA.
Almeida
Jorge R C
JR
Quevedo
Karina
K
Thompson
Wesley K
WK
Terwilliger
Robert A
RA
Hassel
Stefanie
S
Kupfer
David J
DJ
Phillips
Mary L
ML
D000293:Adolescent; D000328:Adult; D016880:Anisotropy; D001714:Bipolar Disorder / Q000175:diagnosis / Q000473:pathology*; D001921:Brain / Q000473:pathology; D003866:Depressive Disorder / Q000175:diagnosis / Q000473:pathology*; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D009434:Neural Pathways / Q000473:pathology*