Small-fiber polyneuropathy SFPN affects unmyelinated and thinly myelinated peripheral axons. Several questionnaires have been developed to assess polyneuropathy from diabeties or chemotherapy, but none for SFPN from other or unknown causes. A comprehensive survey could help clinicians diagnose and assess treatment responses, define prevalence natural history and cures, and identify research subjects. Thus, we developed the one-page Small-fiber Symptom Survey (SSS), using input from patients and 21 medical/scientific experts. Participants comprised consenting consecutive patients evaluated for SFPN at the Massachusetts General Hospital plus normal controls. Participants SFPN status was stratified based on the results of their objective diagnostic tests (distal-leg skin biopsy and autonomic-function testing). We measured internal consistency, test re-test reliability, convergent validity and performed a receiver operating curve analysis.
The 179 participants averaged 46.6±15.6 years old; they were 73.2% female and 92.2% Caucasian. Eighty-five had confirmed SFPN, mostly idiopathic. Principal component analysis revealed 5 symptom clusters. The questionnaire had good internal consistency (Cronbach alpha=0.893), excellent test re-test reliability (r=0.927, p<0.001) and good-to-fair convergent validity. Participants with confirmed SFPN had more severe symptoms than others (p=0.009). The SSS has satisfactory psychometric properties, indicating potential future utility for surveying patient-reported symptoms of SFPN regardless of its cause.
Perspective
This article reports the initial development and early psychometric validation of a new patient-reported outcome measure intended to capture the wide range of multi-system symptoms of small fiber polyneuropathy. Once further developed, it could potentially help clinicians diagnose and monitor patients, and help advance research.