Homotopic stimulation can reduce the area of allodynia in patients with neuropathic pain

Allodynia is a common, troublesome feature of neuropathic pain conditions. In a previous study of postherpetic neuralgia we observed that repeated tactile stimulation appeared to reduce the size of the area of allodynia in some patients. We have undertaken a pragmatic clinical study to characterise this phenomenon in neuropathic pain patients with a range of different aetiologies.Neuropathic pain patients with a discrete area of tactile allodynia were recruited (n=20). We assessed the sensitive area using punctate and dynamic tactile stimuli, and thermal quantitative sensory testing. On two separate testing visits, the patients had repeated (10× over 1min) noxious heat or cotton bud strokes applied to the affected site or contralaterally.Tactile stimulation of the affected area evoked pain (median 7 NRS) and a reduction (>30%) in the area of allodynia in 9/18 patients (maximum −48±9%, after 20min), although the intensity of allodynic pain was unchanged. This effect persisted for over 1h and was present the following day in all patients tested (n=5/5). No subjects showed an increase in area after allodynic stimulation. There was no change in heat pain threshold at a distant site following allodynic stimulation, suggesting no activation of diffuse noxious inhibitory control. Repeated thermal noxious stimulation (median NRS 7) could also elicit changes (>30%) in the area of allodynia in some patients (reductions in 7/20, increases in 3/20).Thus, we have found that a brief period of homotopic painful stimulation can reduce the area of allodynia in around half of patients with established neuropathic pains.