Major Depressive Disorder (MDD) subtypes have been shown to differentially impact psychiatric symptom presentation, clinical features, and functional abilities. While there is extensive research regarding MDD subtypes and clinical characteristics, there has been limited information regarding the relationship between MDD subtypes and neurocognitive functioning. In particular, the neurocognitive impact of the subtype of treatment resistant depression (TRD), defined as MDD that is unresponsive to treatment, is unknown. The aim of this preliminary study was to address this gap by characterizing the neurocognitive profile of TRD. We characterized the performance of older adults with TRD on measures across multiple neurocognitive domains, and explored whether performance varied based on age and education.

Data utilized were drawn from a broader NIMH-funded, randomized, controlled study conducted at the University of New Mexico that investigated the clinical and cognitive outcomes of varying pulse amplitudes during acute electroconvulsive therapy (ECT) in adults with MDD. Participants in the study were age 50+ with a diagnosis of MDD, and further delineated by subtype as TRD. For this analysis, we utilized demographic and baseline neurocognitive data collected prior to start of treatment for those diagnosed with MDD, recurrent, severe (TRD). Neurocognitive measures included the Delis Kaplan Executive Function System (D-KEFS) Verbal Fluency and Color-Word Interference Subtests, Hopkins Verbal Learning Test-Revised (HVLT-R), and the Wechsler Adult Intelligence Scale 4th Edition (WAIS-IV) Digit Spans. Demographic-adjusted scaled scores were computed, and descriptive statistics were used to characterize the demographic and neurocognitive features of the sample. Multiple Analysis of Variance (MANOVA) was used to investigate difference in performance across neurocognitive measures based on level of education, with age as a covariate.

The sample (n = 42) had a mean age of 65 (SD=8), education level between12 and 14 years, 66.6% were female and 93% were Caucasian. DKEFS Verbal Fluency Category Switching Total Switching Accuracy fell in the Average range (Mean SS=9.5, SD=3.1), and Color Word Inhibition Total Completion Time fell in the Average range (Mean SS=8.5, SD=3.3). HVLT-R Total Recall Correct fell in the Mildly Impaired range (Mean T=35.5, SD=9.9) and Delayed Recall Correct fell in the Mildly to Moderately Impaired range (Mean T=32.9, SD=11.0). WAIS-IV Digit Span fell in the Average range (Mean SS=9.5, SD=2.2). Results indicated that age did not adjust outcomes on the neurocognitive variables, Wilks's λ=0.63, F(6, 23)=2.13, p=0.08. We found no evidence for significant effect of level of education on neurocognitive functioning when controlling for the covariate of age, Wilks's λ=-0.16, F(36, 103.7)=1.47, p=0.07.

To our knowledge, this is one of two studies to examine neurocognitive functioning in patients with TRD. The analysis indicated generally intact performance in the neurocognitive domains of executive function (inclusive of verbal fluency, cognitive flexibility, and inhibition), auditory attention and working memory, and Impaired performance on indices of verbal learning and memory. Age did not impact performance on neurocognitive measures, and there was no significant effect for level of education. Further research is warranted to confirm these findings and further explicate the neurocognitive profile of TRD.