Prognostic Factors for Fatigue in Patients With Systemic Lupus Erythematosus

Fatigue will be assessed using the Fatigue Assessment Scale. This tool provides information on the physical and psychological aspects of fatigue. This scale is highly reliable. This self-reported questionnaire consists of 10 items with a 5-point Likert response scale. Five items reflect the physical component and five reflect the psychological component. The score range of the scale is 10-50 (the higher the score, the greater the degree of fatigue).

The State-Trait Anxiety Inventory will be used to measure the presence and severity of anxiety symptoms in patients with systemic lupus erythematosus. There are two subscales within this measure: state and trait. The state anxiety scale assesses the current state of anxiety, while the trait anxiety scale assesses relatively stable aspects of the propensity for anxiety. This scale has 40 items, 20 assigned to each of the subscales, with a range of 1 to 4 points (the higher the score, the higher the level of anxiety).

Quality of life in patients with systemic lupus erythematosus will be measured using the Spanish version of the Lupus Quality of Life (LupusQoL) questionnaire. This questionnaire consists of 34 items in 8 domains (physical health, emotional health, body image, pain, planning, fatigue, intimate relationships, and burden on others). The questionnaire scores range from 0 (worst quality of life) to 100 (best quality of life).

The Spanish version of the Short Form-36 Health Survey (SF-36) questionnaire will be used to measure health-related quality of life. It consists of 36 items that investigate eight dimensions (physical function, physical role, bodily pain, general health, vitality, social function, emotional role, and mental health, including a health transition item). The score ranges from 0 to 100 (better perception of quality of life).

Physical activity level will be assessed using the International Physical Activity Questionnaire (IPAQ). This tool consists of seven questions that inquire about the frequency, duration, and intensity of physical activity performed in the last week. It also assesses the time spent walking and sitting. The results are classified into three categories: low, moderate, and high activity, identifying whether individuals meet the WHO activity recommendations. The unit of measurement is the metabolic equivalent of task (METS), where a higher number of METS indicates greater physical activity.

The Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) is a widely used tool in the evaluation of systemic lupus erythematosus. This global index assesses disease activity over the last 10 days and consists of 24 items that collect specific manifestations in 9 organs or systems. The SLEDAI score ranges from 0 to 105, with higher scores indicating greater disease activity.

The assessment of cumulative damage in patients with systemic lupus erythematosus will be performed using the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SLICC/ACR). The tool includes 12 organ systems and measures irreversible damage from the onset of the disease, regardless of its activity, adverse effects due to treatment, or comorbidities. For damage to be considered, it must have been present for at least six months, thus avoiding confusion with active inflammatory processes. The total index score ranges from 0 to 46, with a higher score indicating a greater degree of cumulative damage.

The sociodemographic variable 'age' will be measured in full months from the patient's date of birth to the date of assessment.

The sociodemographic variable marital status will be measured using 4 response options (qualitative variable): single / married / divorced / widowed.

The sociodemographic variable sex will be measured using a dichotomous variable (Male/Female)

The sociodemographic variable educational level will be measured using 4 response options (qualitative variable): primary education / secondary education / university education / postgraduate education.

The sociodemographic variable employment status will be measured using 4 response options (qualitative variable): self-employed / employed by others / unemployed / disability-retirement.