Cerebellar Volumes Are Smaller in Veterans with PTSD and a History of Mild Traumatic Brain Injury, but Not Mild Traumatic Brain Injury Alone

Mild traumatic brain injury (mTBI), a common health burden among combat veterans, has been associated with alterations in brain structure. Moreover, post-traumatic stress disorder (PTSD), frequently comorbid with mTBI, is linked to smaller cerebellum volumes; however, little is known about whether mTBI (absent comorbid psychiatric symptoms) similarly affects cerebellar structure. The cerebellum may play a central role in common postconcussive symptoms due to its contributions to cognitive and emotional functions. In a sample of 122 combat veterans, we examined whether total cerebellum volumes differed among those with a remote history of mTBI with (n = 29) or without (n = 42) comorbid PTSD and healthy controls (n = 51). An automated cerebellum parcellation protocol was applied to T1-weighted anatomical scans to derive volumetric estimates of the cerebellum (and 28 subregions). Hierarchical regression analysis (adjusting for total intracranial volume, age, sex, and combat exposure) revealed that, compared with controls, participants with comorbid mTBI-PTSD had a significantly smaller volume of the total cerebellum (p = 0.010). There was no significant effect of mTBI-only on total cerebellum volume (p = 0.165). Follow-up exploratory analyses of subregional cerebellum volume differences suggested that volume differences in comorbid mTBI-PTSD were primarily localized to the posterior lobe (crus I, lobules VIIB, VIIIB). In sum, in a sample of combat veterans, mTBI was associated with a smaller volume of the cerebellum, but only when comorbid with PTSD. Consistent with recent work, exploratory subregional analyses indicated that volume differences were primarily attributable to regions of the cerebellum most prominently involved in cognition and emotion. These results underscore the profound effects of PTSD on brain health in military veterans and suggest that mTBI may not produce long-lasting structural damage to the cerebellum. Future work is needed, as it remains possible that subtle cerebellar volume changes may emerge in specific subgroups or as a function of injury-related factors (e.g., mechanism of injury, time since injury) not fully captured in the present study.