Can repetitive transcranial magnetic stimulation increase muscle strength in functional neurological paresis? A proof-of-principle study

Background and purposeTherapeutic options are limited in functional neurological paresis disorder. Earlier intervention studies did not control for a placebo effect, hampering assessment of effectivity. A proof-of-principle investigation was conducted into the therapeutic potential of repetitive transcranial magnetic stimulation (rTMS), using a single-blind two-period placebo-controlled cross-over design. MethodsEleven patients received active 15Hz rTMS over the contralateral motor cortex (hand area), in two periods of 5days, for 30min once a day at 80% of resting motor threshold, with a train length of 2s and an intertrain interval of 4s. Eight of these eleven patients were also included in the placebo treatment condition. Primary outcome measure was change in muscle strength as measured by dynamometry after treatment. Secondary outcome measure was the subjective change in muscle strength after treatment. ResultsIn patients who received both treatments, active rTMS induced a significantly larger median increase in objectively measured muscle strength (24%) compared to placebo rTMS (6%; P<0.04). Subjective ratings showed no difference due to treatment, i.e. patients did not perceive these objectively measured motor improvements (P=0.40). ConclusionsOur findings suggest that rTMS by itself can potentially improve muscle weakness in functional neurological paresis disorder. Whereas patients' muscle strength increased as measured with dynamometry, patients did not report increased functioning of the affected hand, subjectively. The results may indicate that decreased muscle strength is not the core symptom and that rTMS should be added to behavioral approaches in functional neurological paresis.