Objectives:
To assess and measure occurrence of sleep disorders in patients with psoriatic arthritis (PsA) and psoriasis (Ps).

Material and methods:
The study included 62 patients with psoriatic arthritis and 52 patients with psoriasis. The measurement of sleep quality was conducted using the Pittsburgh Sleep Quality Index (PSQI), the evaluation of fatigue by the fatigue subscale of the FACIT-F questionnaire and the patient’s quality of life by the Health Assessment Questionnaire (HAQ). The psoriasis severity was determined using the Psoriasis Area Severity Index (PASI) and the activity of arthritis by the disease activity score of 28 joints (DAS 28). The Visual Analogue Scale (VAS) was used to assess the severity of pain.

Results:
Poor sleep quality was found in 67.7% of PsA patients, 57.7% in Ps patients and 14.6% within the control group. Sleeping disorders in patients with PsA and Ps were related to worse quality of life and intense fatigue. Methotrexate treatment was not related to sleeping disorders, but an improvement in sleep quality was observed in both PsA and Ps patients who were treated with anti TNF- antibodies (p < 0.001 and p = 0.032 respectively). Following the use of the linear regression model, the following factors worsen the sleep quality in PsA: pain (R2 = 0.462, p < 0.001), tender joint count (R2 = 0.434, p < 0.001), C-reactive protein (CRP) concentration (R2 = 0.391, p < 0.001), patient’s age (R2 = 0.284, p = 0.003) and duration of psoriasis (R2 = 0.166, p = 0.006). In Ps patients the factors were: severity of skin lesions (R2 = 0.329, p < 0.001), duration of psoriasis (R2 = 0.290, p = 0.004) and patient’s age (R2 = 0.282, p = 0.019).

Conclusions:
Poor sleep quality in patients with PsA or Ps is a common symptom. Sleep disorders are more frequent in patients with PsA than in those with psoriasis.