The small fiber neuropathy screening list: Construction and cross-validation in sarcoidosis

Small fiber neuropathy (SFN) appears to be relatively common in sarcoidosis patients. However, there is no golden standard to establish SFN and diagnostic tests for SFN are not widely available. There is a need for an easy to administer SFN screening instrument for clinical assessment, research or therapeutic trials. The aim of the present study was to develop a screening list to identify sarcoidosis patients with SFN in general clinical practice.

We studied 139 sarcoidosis patients. The first consecutive 84 patients (Group 1) underwent temperature threshold testing (TTT) and completed an extensive SFN-symptoms-questionnaire. Based on data from Group 1 and using distribution measures and discriminant analyses, a screening list for SFN in sarcoidosis consisting of 21 questions was constructed: the Small Fiber Neuropathy Screening List (SFNSL). Subsequently, this SFNSL was crossvalidated in the next 55 consecutive patients (Group 2).

The same cut-off scores as found for Group 1 were appropriate in Group 2. The SFNSL was found to have high levels of internal consistency (Cronbach's alpha 0.90) and exploratory factor analysis showed that it measures only one underlying factor. Convergent validity seems good.

To assess the presence of SFN in clinical practice the SFNSL, a brief and easy to administer questionaire, was developed in a sarcoidosis population. The results of the present study support the idea that SFN is a serious problem in chronic sarcoidosis. Future studies are needed to establish the broad usefulness of this SFN screening list and expand knowledge on the psychometric properties.