In this study, the effects of pain site and intensity on function were examined in patients with myotonic dystrophy type 1 (DM1) and facioscapulohumeral muscular dystrophy (FSHD) and chronic pain. Questionnaires assessing pain sites, pain extent (number of sites), pain intensity, and pain interference were completed by 182 individuals with DM1 (43%) or FSHD (57%) and chronic pain. There was a positive association between pain extent and intensity with pain interference and a negative association with psychological functioning in both DM1 and FSHD. Pain intensity at specific sites had differential impact beyond the effects of pain intensity alone. Head pain intensity independently affected psychological functioning, while leg, foot, hip, and knee pain independently contributed to the prediction of pain interference. Pain site and intensity differentially modulates the effect of chronic pain on function in DM1 and FSHD patients. Researchers and clinicians should consider these factors when assessing and treating pain.
