Attempts to identify the factor structure in patients with
treatment-resistant depression have been very limited.
Principal component analysis was performed using the baseline datasets from
3 add-on studies [2 with repetitive transcranial magnetic stimulation and one
with transcranial pulsed electromagnetic fields (T-PEMF)], in which the
relative effect as percentage of improvement during the treatment period was analyzed.
We identified 2 major factors, the first of which was a general factor. The
second was a dual factor consisting of a depression subscale comprising the
negatively loaded items (covering the pure depression items) and a treatment
resistant subscale comprising the positively loaded items (covering lassitude,
concentration difficulties and sleep problems). These 2 dual subscales were
used as outcome measures. Improvement on the treatment resistant subscale was
40% in the active treatment group compared to 17-30% improvement in the sham
It is possible to describe patients with therapy-resistant depression by a
factor structure. Both rTMS and T-PEMF had a clinical effect on the
factor-derived scales when compared to sham treatment.