Currently, the management of RA is not only focused on the pharmacological treatment for the control of the activity of the disease, but also in the different disciplines that approach the patients from all aspects and their environment, in order to achieve a management comprehensive therapy that impacts on the prognosis of the disease and their quality of life (18). This strategy is the result of the parallel presence of comorbidities in patients with RA that worsen the functional prognosis of the patient, and which reaches 65.1% of the cases according to the literature (19), a figure similar to what was found in our study (65.2%). In the same way, we have identified the presence of unhealthy lifestyles such as sedentary lifestyle, and smoking or alcohol intake, which increase the burden of disease and increase the risk of incidence of other diseases or the direct complication of RA (20). This coincides with the results of this study since statistically significant associations were identified with a sedentary lifestyle (OR: 1.7 CI 95%: 1.3–2.2) and smoking (OR: 1.7 CI 95%: 1.1–2.6).
The pathophysiology of SDs in RA is still unclear; however, it could be explained by the role played by the immune system, considering that RA is a widespread chronic inflammatory process where humoral and cellular immunity is in constant activity. Thus, changes have been identified in the levels of IL-1, IL-2, IL-6, tumor necrosis factor (TNF), melatonin, intestinal vasoactive peptide, prostaglandins, as well as natural killer cells, which have been shown to be somnogenic and promote deep or slow-wave sleep (21–23). Consequently, these mediators are present in the central nervous system and are directly related to sleep, taking into account that in sleep deprivation these are increased (23), which suggests that during the presence of a chronic inflammatory process the characteristics of sleep may change. Additionally, chronic pain has been associated with quality of sleep or restful sleep, frequent awakenings during the night and time of sleep, becoming a cycle, because pain is also mediated by immunological mechanisms characteristic of RA (7). The study published by Regina et al states that TNF intervenes in narcolepsy, and has been associated with obstructive sleep apnea (OSA) and obstructive sleep apnea-hypopnea syndrome (OSAHS) as well as other SDs, results that are similar in this study, since it identified a relationship between OSAHS and disease activity (OR: 2.2, CI 95%: 1,1–5). This becomes relevant, taking into account that biological medicines are part of the therapy and apparently improve TNF levels (24, 25). Despite this statement, in this study no statistical association was observed between SDs and pharmacological management between conventional and biological DMARDs (OR: 0.9 CI 95%: 0.7–1.2).
SDs in patients with RA have reached prevalence between 38% and 42% (18, 26, 27), which are close to those found in this study (31.1%). These estimates contrast with other studies where prevalence are between 50% and 90%, including a systematic review conducted in 2012 where 23 studies were analyzed with results between 60% and 97% (8, 28, 29). These differences could be explained by the variety of scales used to assess sleep disorders, as well as the specific and directed search since in most cases a comprehensive approach to the patient is not made.
With regards to the demographic characteristics of the population, the literature shows that SDs in patients with RA occur more frequently between the fifth and sixth decade of life (18), which for this study showed differences from the statistical point of view (p = < 0.001). In the same way, the association between schooling and socioeconomic classification was explored (Table 2) finding an association with the presence of SDs, which for the case of schooling the subjects with the highest academic level (secondary or university) have fewer SDs, assuming that there is a relationship between knowledge, understanding, and perception of the disease with adherence and self-care, hence the decrease in comorbidities (30). With respect to the realization of self-care activities, where the execution of manual activities, exercise, participation in social groups and collectives, the present study showed a significant association (Table 2), concordant with the literature, since it has been demonstrated to be a factor that reduces the clinical and symptomatic activity of RA and also decreases the appearance of comorbidities, directly impacting on the characteristics of sleep, specifically in restful sleep (31) .
Clinimetric values such as DAS28 and HAQ are related to the presence of SDs. Xu et al, in a study with 71 subjects with RA, determined that SDs affect the activity of RA (DAS28, r = 0.46, p < 0.01) and quality of life (HAQ, r = 0.36, p < 0.01), results that are not far from those found in our cohort of patients, which showed significant differences in these two scales with respect to the presence of SDs (Fig. 1). These values suggest a close relationship between these two pathologies that, according to the theories proposed in their physiopathology, the treatment with biological drugs and the comprehensive care programs that show an improvement in the activity of the disease and in the same way decreases SDs (27). In the same way, an association with metabolic pathologies such as diabetes and dyslipidemia could be determined (p: <0.001), which can be explained by the association between nocturnal hypoxia and fragmentation of sleep and diabetes, since some studies have been able to identify sleep disturbances, increased oxidative stress, neurohumoral changes, and systemic inflammation, which favor insulin resistance. This relationship can be increased in the presence of an autoimmune process such as RA; however, due to the characteristics of this study, the temporal causal relationship cannot be determined (32).
It is important to mention that the presence of SDs can be associated with other comorbidities such as obesity (33), chronic pulmonary pathologies, neurodegenerative processes, which can be the main cause of SDs as a result of a chronic inflammatory process, as well as for other causes before the diagnosis of RA, however, it has been argued that concomitance with RA can trigger or potentiate SDs due to changes related to pain and the impacts of immunological mediators on the central nervous system, for which disease activity can be associated (25, 34).
According to what has been described, the recommendations for the treatment of RA should be aimed at achieving the objectives of activity in a comprehensive care program (35, 36), which takes into account the quality of life of the patient and the incidence of SDs that directly impact the symptom control, the prevention of structural damage and their functional integration into society (37, 38). These interventions of cognitive and behavioral order are effective for pain management and coping, and other general patient health aspects, displaying objective improvement in pain rating, the number of affected joints, decrease in reports of sexual alterations, the incidence of psychiatric pathologies, and SDs (7, 39).
Finally, it is relevant that health professionals who are part of the comprehensive treatment team explore the different comorbidities that occur in patients with RA, which for the case of SDs, symptom identification would allow a marked improvement in the quality of the patient's life and, therefore, better control of the disease.