• Elena K Enax-Krumova, Melanie Lenz, Jule Frettlöh, Oliver Höffken, Annika Reinersmann, Andreas Schwarzer, Andrea Westermann, Martin Tegenthoff, and Christoph Maier.
• Departments of Neurology, BG University Hospital Bergmannsheil GmbH, Ruhr University Bochum, Bochum, Germany.
• Pain Med. 2017 Jan 1; 18 (1): 95-106.

ObjectiveThe most prominent sensory sign of the complex regional pain syndrome (CRPS) is blunt hyperalgesia, but longitudinal studies on its relation to the outcome of long-term multimodal treatment are lacking.MethodsWe examined 24 patients with CRPS type I using standardized Quantitative Sensory Testing on the affected hand and the contralateral hand at baseline and 6 months following treatment. Somatosensory evoked potentials after single and paired-pulse stimulation of the median nerve were performed to assess the paired-pulse suppression (n = 19). Treatment response at follow-up was defined as pain relief > 30% and improved hand function. Statistics: Wilcoxon test, Pearson correlation.ResultsAt baseline, similar to previous studies, the pressure pain threshold (PPT) was significantly decreased and the pain response to repeated pinprick stimuli was significantly increased, while all detection thresholds were within the normal range without any difference between the later treatment responders and non-responders. After 6 months of treatment, the PPT increased significantly in the whole study group. However, the pressure hyperalgesia improved only in treatment responders (n = 17, P  < 0.05), whereas there was no improvement in non-responders (n = 7). The rest of the sensory profile remained nearly unchanged. There was a correlation between the paired-pulse suppression and the PPT only at follow-up (r = 0.49, P  < 0.05), but not at baseline, where low pressure pain threshold was associated with impaired paired-pulse suppression.ConclusionThus, the persistence of blunt hyperalgesia seems to be associated with impaired paired-pulse suppression, both representing maladaptive central nervous changes in CRPS, which may account for the treatment non-response in this subgroup.

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