Trajectories of depression and anxiety symptoms during psychological therapy for common mental health problems

Background: There is substantial variation in patient symptoms following psychological therapy for depression and anxiety. However, reliance on endpoint outcomes ignores additional interindividual variation during therapy. Knowing a patient’s likely symptom trajectories could guide clinical decisions. Aim: Identify latent classes of patients with similar symptom trajectories over the course of psychological therapy and explore associations between baseline variables and trajectory class. Method: Patients received high-intensity psychological treatment for depression or anxiety at NHS Improving Access to Psychological Therapies (IAPT) services in South London (N = 16,258). To identify trajectories, we performed growth mixture modelling of depression and anxiety symptoms over 11 sessions. We then ran multinomial regressions to identify baseline variables associated with trajectory class membership. Results: Trajectories of depression and anxiety symptoms were highly similar and best modelled by four classes. Three classes started with moderate-severe symptoms and showed (1) minimal change, (2) gradual improvement, and (3) fast improvement. A final class (4) started with mild symptoms and demonstrated small improvement. Within the trajectory classes with moderate-severe baseline symptoms, patients in the two classes showing improvement as opposed to minimal change tended not to be prescribed psychotropic medication or report a disability and were in employment. Those showing fast improvement additionally reported lower baseline functional impairment on average. Conclusion: Multiple trajectory classes of depression and anxiety symptoms were associated with baseline characteristics. Identifying the most likely trajectory for a patient at the start of treatment could inform decisions about the suitability and continuation of therapy, ultimately improving patient outcomes.