Dosing transcranial magnetic stimulation in major depressive disorder: Relations between number of treatment sessions and effectiveness in a large patient registry

Background: The number of sessions in an acute TMS course for major depressive disorder (MDD) is greater than in the earlier randomized controlled trials. Objective: To compare clinical outcomes in groups that received differing numbers of TMS sessions.Methods: From a registry sample (N = 13,732), data were extracted for 7215 patients treated for MDD with PHQ9 assessments before and after their TMS course. Groups were defined by number of acute course treatment sessions: 1-19 (N = 658), 20-29 (N = 616), 30-35 (N = 1375), 36 (N = 3591), 37-41 (N = 626), or >41 (N = 349) and compared in clinical outcomes at endpoint and at fixed intervals (after 10, 20, 30, and 36 sessions). The impact of additional treatments beyond 36 sessions was also examined.Results: Groups that received fewer than 30 sessions had inferior endpoint outcomes than all other groups. PHQ-9 symptom reduction was greatest in the group that ended treatment at 36 sessions. The extended treatment groups (>36 sessions) differed from all other groups by manifesting less antidepressant response early in the course and had a slower but steady rate of improvement over time. Extending treatment beyond 36 sessions was associated with further improvement without evidence of a plateau.Conclusions: In real-world practice, there are strong relations between the number of TMS sessions in a course and the magnitude of symptom reduction. Courses with less than 30 sessions are associated with diminished benefit. Patients with longer than standard courses typically show less initial improvement and a more gradual trajectory, but meaningful benefit accrues with treatment beyond 36 sessions.