Longitudinal Diagnostic Reassessment and Multimodal Treatment in Difficult-to-Treat Depression: A Case Report

Background: Severe depressive illness may remain symptomatic despite multiple evidence-based treatments, while diagnostic formulation may evolve as longitudinal information accumulates. The difficult-to-treat depression (DTD) framework may be particularly relevant when sustained remission remains elusive and management requires sequential or overlapping interventions. Case presentation: We describe a longitudinal case of a predominantly depressive illness beginning in adolescence, with recurrent severe episodes, suicidality, numerous psychiatric hospitalizations, and extensive treatment exposure across different healthcare systems. The illness was initially conceptualized within the schizoaffective spectrum and was later reformulated as recurrent depressive disorder following longitudinal reassessment. Treatment included pharmacotherapy, psychotherapy, electroconvulsive therapy (ECT), repeated intranasal esketamine, and implanted vagus nerve stimulation (VNS). ECT produced clinically meaningful but time-limited improvement, while esketamine and VNS became components of longer-term multimodal management. During repeated esketamine treatment, the patient reported changes in acute perceptual phenomena and differences in subjective experience according to auditory context, including self-selected use of binaural-beat music. A temporary qualitative change in the esketamine experience was also reported after ECT. These uncontrolled observations are presented as hypothesis-generating rather than evidence of a therapeutic interaction. Conclusions: This case illustrates the importance of longitudinal diagnostic reassessment and of distinguishing diagnostic revision from retrospective invalidation of earlier formulations. It also demonstrates the limitations of attributing improvement to individual treatments when interventions with different therapeutic timescales are used sequentially and concurrently. In severe DTD, clinically meaningful outcomes may extend beyond categorical remission to include reductions in suicidality and symptom burden and improvements in functioning. Detailed patient-reported phenomenology may complement standardized assessment and generate questions for prospective investigation, but should be interpreted cautiously when derived from an uncontrolled individual case.