Validation of the composite autonomic symptom scale 31 (COMPASS-31) in patients with and without small fiber polyneuropathy

Background and purposeThe recently developed composite autonomic symptom score 31 (COMPASS-31) is a questionnaire that assess symptoms of dysautonomia. It was distilled from the well-established Autonomic Symptom Profile questionnaire. COMPASS-31 has not yet been externally validated. To do so, its psychometric properties and convergent validity in patients with and without objective diagnosis of small fiber polyneuropathy (SFPN) were assessed. MethodsInternal validity and reliability of COMPASS-31 were assessed in participants with or without SFPN spanning the full range of severity of autonomic symptoms. Convergent validity was assessed by comparing results of the COMPASS-31 with the gold standard autonomic function testing that measures cardiovagal, adrenergic and sudomotor functions. Additionally, relationships between COMPASS-31 and the Short Form McGill Pain Questionnaire, Short Form Health Survey and 0-10 numeric pain scale were measured. COMPASS-31 and all other questionnaire results were compared between patients with or without evidence of SFPN, objectively confirmed by distal-leg PGP9.5-immunolabeled skin biopsy. ResultsAmongst 66 participants (28 SFPN+, 38 SFPN-), COMPASS-31 total scores had excellent internal validity (Cronbach's =0.919), test-retest reliability (r(s)=0.886; P<0.001) and good convergent validity (r(s)=0.474; P<0.001). COMPASS-31 scores differed between subjects with or without SFPN (Z=-3.296, P<0.001) and demonstrated fair diagnostic accuracy. Area under the Receiver Operating Characteristic curve was 0.749 (P=0.01, 95% confidence interval 0.627-0.871). ConclusionsCOMPASS-31 has good psychometric properties in the population of patients being evaluated for SFPN and thus it might be useful as an initial screening tool for the more expensive SFPN objective tests.