Repetitive transcranial magnetic stimulation of the parietal cortex transiently ameliorates phantom limb pain-like syndrome

Objective: Phantom pain is linked to a reorganization of the partially deafferented sensory cortex. In this study we have investigated whether the pain syndrome can be influenced by repetitive transcranial magnetic stimulation (rTMS). Methods: Two patients with a longstanding unilateral avulsion of the lower cervical roots and chronic pain in the arm were studied. As a control the acute effects of rTMS (15 Hz, 2 s duration) on pain were studied in 4 healthy subjects. Pain intensity was assessed with the Visual Analogue Scale. Results: Stimulation of the contralateral parietal cortex led to a reproducible reduction in pain intensity lasting up to 10 min. Stimulation of other cortical areas produced only minor alterations in the severity of the pain. Both 1 and 10 Hz rTMS trains applied to the contralateral parietal cortex on weekdays for 3 consecutive weeks did, however, not lead to permanent changes in the pain intensity. Experimentally induced pain (cold water immersion of the right hand) in normal subjects was not influenced by rTMS. Conclusions: These results do not favor the use of rTMS in the treatment of phantom limb pain. The results, however, support the concept that phantom pain is due to a dysfunctional activity in the parietal cortex. The transient rTMS-induced analgesic effect may be due to a temporary interference with the cerebral representation of the deafferented limb.