Prevalence of autonomic nervous system dysfunction in complex regional pain syndrome

We aimed to investigate the prevalence of dysautonomia in complex regional pain syndrome (CRPS) via the combined autonomic nervous system (ANS) function tests, including the deep breathing test (DBT), orthostatic test (OST) and sympathetic skin response (SSR).

We retrospectively examined 263 patients who underwent the combined ANS tests to evaluate CRPS between August 2013 and December 2016. Based on the Budapest clinical criteria, patients were stratified into confirmed-CRPS or suspected-CRPS groups. We performed binary logistic regression analysis using the inverse probability of treatment weighting to investigate the association between the tests and CRPS. Sensitivity and specificity were calculated to assess the diagnostic performance of the ANS tests for CRPS. We compared the results of these tests between the outcomes of sympathetic nerve blocks (SNBs).

Among 247 patients, finally included in this study, 199 patients (80.6%) were diagnosed with CRPS. Abnormal results of overall or each ANS function test showed significant associations with CRPS, excluding OST (overall abnormality: OR 2.44, 95% CI 1.51 to 3.95; p<0.001; DBT: OR 2.57, 95% CI 1.23 to 5.38, p=0.013; OST: OR 1.88, 95% CI 0.92 to 3.84, p=0.085; SSR: OR 2.71, 95% CI 1.38 to 5.32, p=0.004). However, their prevalence in CRPS and their sensitivities for CRPS were low (overall abnormality: 26.1%; each test: <15%). No significant association existed between dysautonomia and SNB outcomes.

Dysautonomia, as evaluated using the combined ANS tests, were observed in a small portion of patients with CRPS. The diagnostic performances of these tests for CRPS were inadequate for clinical purposes.