Pain threshold and temporomandibular function in systemic sclerosis: comparison with psoriatic arthritis

The aim of the study was to evaluate whether a reduced pain threshold is associated with increased temporomandibular dysfunction in systemic sclerosis (SSc) compared to psoriatic arthritis (PsA) and healthy controls. Ninety subjects participated in the study (30 SSc, 30 PsA, and 30 healthy controls). The Helkimo index was used to evaluate temporomandibular dysfunction. Digital palpation was performed at the temporomandibular joint (TMJ) surface and at the superficial masseter muscle (SMM) and pain intensity was recorded on a visual analog scale (VAS), while pain pressure threshold (PPT) was measured at the same sites through a pressure algometer. PPT scores were lower in SSc patients compared to PsA patients and controls. In addition, the average Helkimo index score, measuring the degree of TMJ dysfunction, was higher in SSc compared to PsA and controls. A significant inverse correlation was observed between every PPT score, and both Helkimo index and VAS palpation in SSc and PsA. Both the range of motion and all the other pain-related subdomains of the Helkimo index score (pain on movement, pain palpation TMJ and pain palpation muscle) were significantly worse in SSc compared to PsA, while no significant differences were observed in the TMJ function subdomain. In SSc patients, the skin score was directly associated with the range of motion subdomain of the Helkimo index. Our results confirm that TMJ function is impaired in SSc; further longitudinal studies are needed to assess the role of pain threshold in the assessment of limitations in TMJ function and to identify an objective marker of therapeutic response.