Abstract
Achieving perceptual gains in healthy individuals or facilitating rehabilitation in patients is generally considered to require intense training to engage neuronal plasticity mechanisms. Recent work, however, suggested that beneficial outcome similar to training can be effectively acquired by a complementary approach in which the learning occurs in response to mere exposure to repetitive sensory stimulation (rSS). For example, high-frequency repetitive sensory stimulation (HF-rSS) enhances tactile performance and induces cortical reorganization in healthy subjects and patients after stroke. Patients with complex regional pain syndrome (CRPS) show impaired tactile performance associated with shrinkage of cortical maps. We here investigated the feasibility and efficacy of HF-rSS, and low-frequency rSS (LF-rSS) to enhance tactile performance and reduce pain intensity in 20 patients with CRPS type I. Intermittent high- or low-frequency electrical stimuli were applied for 45 min/day to all fingertips of the affected hand for 5 days. Main outcome measures were spatial two-point-discrimination thresholds and mechanical detection thresholds measured on the tip of the index finger bilaterally. Secondary endpoint was current pain intensity. All measures were assessed before and on day 5 after the last stimulation session. HF-rSS applied in 16 patients improved tactile discrimination on the affected hand significantly without changes contralaterally. Current pain intensity remained unchanged on average, but decreased in four patients by ≥30%. This limited pain relief might be due to the short stimulation period of 5 days only. In contrast, after LF-rSS, tactile discrimination was impaired in all four patients, while detection thresholds and pain were not affected. Our data suggest that HF-rSS could be used as a novel approach in CRPS treatment to improve sensory loss. Longer treatment periods might be required to induce consistent pain relief.
Highlights
The complex regional pain syndrome (CRPS) is a chronic pain syndrome, which is characterized by sensory, autonomic, and motor disturbances [1, 2]
Translating protocols used in long-term potentiation (LTP), or long-term depression (LTD) studies to sensory stimulation experiments in humans, it could be shown that high-frequency repetitive somatosensory stimulation (rSS) (HF-rSS) improved tactile acuity, while in contrast the application of low-frequency rSS (LF-rSS) lead to impaired tactile discrimination performance [26]
On the non-affected hand, the mechanical detection threshold (MDT) did not significantly change, there was a clear trend toward lower MDTs (1.28 ± 0.26 mN, p = 0.25)
Summary
The complex regional pain syndrome (CRPS) is a chronic pain syndrome, which is characterized by sensory, autonomic, and motor disturbances [1, 2]. It is subdivided into type I without and type II with nerve lesion. Aside from pharmacological treatment, rehabilitation based on concepts to induce neuroplasticity [11], such as sensory training, mirror therapy, or graded motor learning, are currently used to improve the sensorimotor limb function and to reduce pain [9, 12,13,14,15,16]. Among other deficits, patients with CRPS show reduced tactile discrimination performance in combination with a shrunken cortical representation of the affected hand [9, 12, 29,30,31,32,33], rSS might be a promising intervention for an additional non-pharmacological concept in the treatment of CRPS
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