Complex Regional Pain Syndrome (CRPS) is clinically characterized by pain in combination with sensory, autonomic, and motor symptoms that may include weakness, tremor, myoclonus and dystonia of the affected limb(s). The syndrome is multifactorial in origin and mostly attributed to tissue injury. There is some evidence that the human leukocyte antigen (HLA) system plays a role in the pathophysiology of CRPS, but previous studies lacked power. Here we performed the most extensive study investigating the contribution of HLA alleles (i.e. HLA-A, HLA-B, HLA-DRB1, and HLA-DQB1) in 150 CRPS patients who also had fixed dystonia. HLA-B62 (OR=2.05 [95% CI 1.41-2.99], P=0.0005) and HLA-DQ8 (OR=1.75 [95% CI 1.20-2.57], P=0.005) were found significantly associated with CRPS and dystonia. The association remained significant after correction (HLA-B62 P(corrected) [P(c)] = 0.02 and HLA-DQ8 P(c)=0.04). The involvement of HLA-B62 and HLA-DQ8 in CRPS with dystonia may indicate that these HLA loci are implicated in the susceptibility or expression of the disease.

Genetic factors are suggested to play a role in complex regional pain syndrome (CRPS), but familial occurrence has not been extensively studied. In the present study we evaluated familial occurrence in Dutch patients with CRPS. Families were recruited through the Dutch Association of CRPS patients and through referral by clinicians. The number of affected members per family, the phenotypic expression and inheritance were assessed. Demographic and clinical characteristics of familial CRPS (fCRPS) patients were compared with those of sporadic CRPS (sCRPS) patients from a Dutch population-based study and with a group of sCRPS patients that was proportionally matched for referral center of the fCRPS probandi to control for referral bias. Thirty-one CRPS families with two or more affected relatives were identified, including two families with five, four with four, eight with three and 17 with two affected relatives. In comparison with sCRPS patients, fCRPS patients had a younger age at onset and more often had multiple affected extremities and dystonia. We conclude that CRPS may occur in a familial form, but did not find a clear inheritance pattern. Patients with fCRPS develop the disease at a younger age and have a more severe phenotype than sporadic cases, suggesting a genetic predisposition to develop CRPS.

Complex Regional Pain Syndrome (CRPS) usually develops after a noxious event, but spontaneous onsets have been described in 3-11% of the cases. The existence of spontaneous-onset CRPS is highly debated and the aim of the present study was therefore to compare the phenotypic characteristics of CRPS patients with a spontaneous onset, with those of patients with a trauma-induced onset. Data of 537 CRPS patients followed up at four departments of anesthesiology were analyzed and comprised 498 (93%) patients with and 39 (7%) patients without a known eliciting event. There where no significant differences between the two groups in gender, or in onset in upper or lower limb or left or right side of the body. Compared to CRPS patients with a trauma-induced onset, spontaneous-onset cases were on average 9 years younger at disease onset and had a 1.4 years longer median disease duration. No significant differences in frequency were found for any of the 34 compared signs and symptoms when the effect of multiple testing was controlled. In conclusion, CRPS may develop both with and without a precipitating noxious event, with both groups exhibiting a largely similar clinical presentation. Spontaneous-onset CRPS patients generally develop the syndrome at a younger age, possibly indicating a susceptibility to develop the condition. The longer disease duration in spontaneous-onset cases may reflect a more gradual disease onset, poorer prognosis, or a delay in diagnosis, possibly as a result of reluctance to make this diagnosis in the absence of a clear initiating event.

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Complex regional pain syndrome type 1 (CRPS-1) is a chronic pain disorder that in some patients is associated with fixed dystonia. The pathogenesis of CRPS and its relation to dystonia remain poorly understood. Several genes (so-called DYT genes) identified in other causes of dystonia play a role in mechanisms that have been implicated in CRPS. Because different mutations in the same gene can result in diverse phenotypes, we sequenced all coding exons of the DYT1, DYT5a, DYT5b, DYT6, DYT11, DYT12, and DYT16 genes in 44 CRPS patients with fixed dystonia to investigate whether high-penetrant causal mutations play a role in CRPS. No such mutations were identified, indicating that these genes do not seem to play a major role in CRPS.