Explanatory Factors and Predictors of Fatigue in Patients With Sjögren's Disease: A 3-month Longitudinal Study

The MFI-20 is a 20-item self-reported questionnaire assessing fatigue across five dimensions: general fatigue, physical fatigue, mental fatigue, reduced motivation, and reduced activity. Each item is scored on a 5-point Likert scale. Total scores range from 20 to 100, with higher scores indicating greater fatigue.

ESSDAI is a clinician-reported index assessing systemic disease activity in Sjögren's syndrome across multiple domains including constitutional, glandular, articular, cutaneous, pulmonary, renal, muscular, peripheral and central nervous system, hematological, and biological features. Higher scores indicate greater disease activity.

ESSPRI is a patient-reported outcome measure evaluating fatigue, pain, and dryness using a 0-10 numerical rating scale. The final score is calculated as the mean of the three domains. Higher scores indicate worse symptom severity.

PPT will be assessed using a digital pressure algometer applied at a constant rate of 50 kPa/s with a 1 cm² probe. Measurements will be taken bilaterally at predefined anatomical sites (trapezius muscle, thumb nail base, and knee). The mean of three consecutive measurements at each site will be recorded. A global PPT value will be calculated by averaging all sites. Higher values indicate lower pain sensitivity.

HADS is a 14-item self-report questionnaire assessing anxiety and depression. It consists of two subscales (anxiety and depression), each ranging from 0 to 21. Higher scores indicate greater psychological distress.

The PCS is a 13-item self-report questionnaire assessing catastrophic thinking related to pain. Each item is rated on a 5-point Likert scale (0-4), with total scores ranging from 0 to 52. Higher scores indicate greater levels of pain catastrophizing. The scale includes three subdomains: rumination, magnification, and helplessness.

The PSQI is a 19-item self-reported questionnaire assessing sleep quality over the past month. It generates a global score ranging from 0 to 21, with higher scores indicating poorer sleep quality. The instrument evaluates seven components including sleep quality, latency, duration, efficiency, disturbances, use of sleep medication, and daytime dysfunction.

The IPAQ-SF is a 7-item questionnaire assessing physical activity levels over the last 7 days, including walking, moderate-intensity, and vigorous-intensity activities. Total physical activity is expressed as MET-minutes per week. Higher scores indicate higher levels of physical activity.