The Pain Dynamics of Small Fiber Neuropathy

Pain is a central feature in small fiber neuropathy (SFN), with only moderate effects of pharmacologic treatment. The evaluation of the efficacy of therapies on pain has been driven by static measures, and a circadian cycle has been suggested. The aim of this study is to evaluate the pain dynamics in SFN. A total of 165 patients completed a standardized pain diary 4 times per week over a 4-week period. Patients used the 11-point numeric rating scale for average diurnal, nocturnal, and maximum pain, taking into account the circumstances in which pain emerged most. Medication used, SFN-related complaints, sleep quality, and anatomic location of pain were also assessed. Neuropathic pain showed a length-dependent pattern. For pain intensity, marginal higher pain scores at night than during the day were shown, likely not clinically meaningful, with stable lower pain intensities in weekends compared with weekdays. The average pain intensity was stable during the 4-week period. Maximum pain was experienced mainly at rest and during sleep. Besides, pain intensity at night showed an inverse relationship with quality of sleep. In conclusion, for trials in SFN it is justified to use pain scores from any time of the day during short measurement periods. Perspective: This article presents for the first time the pain dynamics of SFN. The effect of pharmacologic treatment in SFN is often disappointing, partly owing to insufficient trial designs. The results of this study have added value in the development of new proper clinical trials in SFN.