Objectives: To study whether poor sleep and comorbidities are associated with high symptom levels of patient-reported outcomes (PROs) pain, patient global assessment and fatigue in patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA), in a nation-wide cross-sectional setting.

Methods: Clinical data were extracted from The Finnish Rheumatology Quality Register between 1.2021 and 9.2022. Self-reported sleep was categorized as "good" (little/no difficulties) or "poor" (great difficulties/can't) sleep. Data concerning comorbidities were collected from national registers. Descriptive statistics were used. Regression analyses were applied to analyze independent associations of sleep status, comorbidities and disease activity with pain in RA and PsA, adjusting for age and sex.

Results: Among 13,512 patients with RA, 6052 [mean (SD) age 62 (13), 71% female] had sleep status reported; in PsA 1861/3636 [age 55 (13), 48% female]. In RA, 5072 (84%) reported good and 980 (16%) poor sleep; the corresponding numbers in PsA were 1460 (78%) and 401 (22%). Median values for objective disease activity were low and similar in patients with poor sleep and good sleep in both diseases. Among patients with no swollen joints, the median values for PROs were approximately three times higher for patients with poor sleep vs. good sleep in both diagnoses (P<0.001). In regression analyses, "poor" sleep was independently associated with higher symptoms in pain [B (95%CI) 20 (18,22) in RA and 23 (19, 26) in PsA], followed by comorbid fibromyalgia, as well as depression in RA and sleep apnea in PsA.

Conclusion: "Poor" sleep quality and comorbidities are independently associated with pain. Patient's sleep status is important to know especially in patients with severe symptoms without objective disease activity.