Treatment-related changes during and after inpatient treatment for refractory somatic symptom disorder or functional neurological symptom disorder: testing the applicability of a new approach for analyzing routine outcome monitoring data

The aim of the current observational study was to examine changes and the moments of change during and after intensive integrated multidisciplinary inpatient treatment for patients with refractory Somatic Symptom Disorder (SSD) or Functional Neurological symptom Disorder (FND). Observational Routine Outcome Monitoring (ROM) data were analyzed to examine changes during and after tertiary care inpatient treatment. Treatment was a combination of acceptance and commitment therapy, body-oriented mentalization therapy, psychophysiology therapy, and systemic therapy. Fifty-five inpatients were included. Eight domains of health status (RAND-36) and symptoms of psychopathology (BSI) were analyzed with multiple-lag two-phase mixed model regression analysis. In this new approach, a series of regression analyses evaluated changes and the moments of change (i.e., the improvement lag). Graphs were created for each outcome measure to visualize estimates and significances as a function of all lags explored. A Monte Carlo validation study with simulated data demonstrated the applicability of this approach. Regarding the RAND-36, the most pronounced and significant (p