Transcranial magnetic stimulation (TMS) is an effective treatment for individuals with pharmacoresistant major depressive disorder (MDD), yet identifying which patients best respond remains an important area of inquiry. The Brief Symptom Inventory (BSI-18) serves as a screen for psychological distress, providing measures across three separate domains (e.g., somatization, depression, and anxiety) and one composite score (i.e., global severity index). The psychometric properties of the BSI-18 have been validated across multiple studies; however, it has sparsely been used to track changes in patient symptoms in response to intervention. Assessing patient symptom severity across these domains is imperative since these symptoms can negatively influence cognitive functioning. Accordingly, the current study utilized the BSI-18 to measure psychological distress across these different domains in patients receiving TMS treatment. We hypothesized that all domains of the BSI-18 would see a significant decrease after treatment, that elevated scores in specific domains would predict a less favorable response to treatment, and that measurement of depressive symptoms will be consistent across measures of similar scope.

Veterans (n=94) with MDD and met standard clinical TMS criteria were administered the BSI-18 before and after receiving an adequate dose of treatment (e.g., 30 sessions). Paired Samples T-test were used to compare the pre-treatment and post-treatment scores across domains.

The results of paired sample t-tests indicated a statistically significant reduction in measures of global psychological distress (t(93) = 7.99, p < .001, Cohen's d =.82), as well as depressive (t(93) = 8.34, p < .001, d = .86), anxious (t(93) = 7.64, p < .001, d = .79), and somatic symptoms (t(92) = 5.29, p < .001, d = .55) after receiving treatment. Individuals with elevated levels of anxiety (e.g., BSI-A>63) saw a significant reduction in depressive (t(62) = 8.15, p < .001, d = 1.03), anxious (t(62) = 8.34, p < .001, d = 1.05) and somatic (t(61) = 4.94, p < .001, d = .63) symptoms. Lastly, two measures of depressive symptoms, the BSI-D and PHQ-9, had a statistically significant strong, positive relationship before (r=.66) and after (r=.88) treatment (all n=65 and p<.001).

The BSI-18 can detect changes in different domains of psychological distress as a function of TMS treatment. Unexpectedly, TMS patients with elevated levels of anxiety responded well to treatment despite comorbid anxiety often being associated with less favorable outcomes in treatment trials. The positive relationship of the BSI-D and PHQ-9 before and after treatment suggests the use of the BSI as a valid, additional measure of depressive symptoms.