From Autoimmune Sialadenitis to Central Pain: Hypothesizing Shared Pathogenesis for Fibromyalgia and Primary Sjogren’s Disease and Identifying Essential Screening Strategies

Even though primary Sjögren disease (pSjD) is mainly associated with sicca symptoms, there are extraglandular manifestations of the disease which affect the quality of life of patients the most and may even be life-threatening. Among the most severe, polyneuropathy and myopathy are worth mentioning. Additionally, clinical observations suggest a higher prevalence of fibromyalgia (FM) in this group of patients, clouding physicians' assessment and potentially leading to unsuccessful therapeutic decisions. The aim of our study was to evaluate the frequency of pSjD and FM co-occurrence as well as to find the most effective screening tools and markers of such overlap. A total of 97 consecutive patients with diagnosed pSjD were incorporated in the study after obtaining their informed consent. Participants completed a set of broadly available questionnaires, including Fibromyalgia Survey Questionnaire, SF-36 and EULAR Sjögren's Syndrome Patient-Reported Index (ESSPRI). Data on their laboratory results was collected in the dedicated database. Moreover, patients underwent electroneurographic (ENG) and electromyographic (EMG) testing. Central nervous system (CNS) abnormalities were detected using MRI. Objective disease activity was evaluated based on EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI). The mean age was 55.3 (range 19.0-78.0 years, SD = 13.9). The disease duration ranged from 2 to 42 years (M = 9.03 years, SD = 7.1 years). Nearly half of the participants (n = 44, 45%) met diagnostic criteria of FM. Interestingly, the diagnosis of FM correlated with CNS involvement. There was no significant correlation between FM and either polyneuropathy/myopathy nor laboratory findings (however, C3c and folic acid concentrations were near the level of significance-mean 1.2 vs. 1.29; <i>p</i> = 0.075 and mean 11.35 vs. 9.21; <i>p</i> = 0.071, respectively). Within the subcategories of SF-36 and ESSPRI scales, significant positive correlation was noted with ESSPRI total score and ESSPRI pain score (neuropathic subcategory), while a negative correlation was found with SF-36 vitality score, physical functioning score, and the SF-36 total score. FM is common among pSjD patients and should be considered rather a comorbidity requiring different therapeutic approaches. At the fast-paced clinical environment, a concise ESSPRI assessment may be helpful in the initial screening of patients at risk of FM. Even though the origin of this phenomenon is unknown, the concepts of central sensitization and microglia polarization may be potential explanations and more molecular research in this direction could benefit the pSjD patients.