Chronic pain, somatic unexplained complaints and multimorbidity: A mutimorbidity painful syndrome?

Introduction: Chronic illnesses are a major research challenge due to its implications in aging and quality of life of adults and elders, and it can be associated with chronic illnesses and other complaints. The objective of this study was to investigate the role of morbidities (chronic diseases with or without somatic unexplained symptoms) and somatic unexplained complaints in a hypothetical model of a multimorbidity painful syndrome. Our hypothesis is that chronic pain should be considered part of a syndrome that includes other chronic diseases and pathological states, especially conditions with somatic unexplained symptoms, and fibromyalgia is one of the evidence on that. Methods: A pilot sample of 306 subjects was investigated in this study (254; 83.0% with chronic pain). The following features were investigated: demographic data, chronic diseases (classified as with or without somatic unexplained symptoms), medications in use, pain characteristics, fulfillment of diagnostic criteria of fibromyalgia, and somatic unexplained complaints (gastric complaints, sleep disturbances, numbness, and the dry mucosa score). Statistical analysis included descriptive data, tested with chisquare, Fisher's exact, nonpara-metric Kolmogorov-Smirnoff, Student's t test; data normalization with Z-score; Pearson's coefficient for correlation, two-steps cluster classification, multivariate linear regression, LASSO and logistic regression. Results: Both groups of chronic diseases were more prevalent in the group of patients (p < 0.001 and p = 0.013, respectively), which had higher frequency of somatic unexplained complaints (gastrointestinal, dry mucosa and numbness) than controls. There was a high positive correlation between number of pain areas and somatic unexplained symptoms score (R-2 = 0.626; p < 0.001), and diseases with these symptoms were a risk factor for chronic pain (R-2 = 0.5748) and fibromyalgia (AlC = 5.8952). Conclusions: Diseases with somatic unexplained symptoms and somatic unexplained complaints were associated with chronic pain, including fibromyalgia. They may be risks factors for pain spread. The findings support that chronic pain could be further investigated as part of a multimorbid syndrome, which should be better assessed to improve aging and quality of life of patients.