Cross-Cultural Adaptation and Psychometric Evaluation of the Italian Version of the Systemic Lupus Erythematosus Symptom Checklist

Background/Objectives: Systemic lupus erythematosus (SLE) causes a wide, fluctuating range of disease- and treatment-related symptoms that objective indices capture only partially. The SLE Symptom Checklist (SSC) is a disease-specific patient-reported measure of symptom occurrence and perceived burden, but no Italian version exists, and its latent structure has never been examined with confirmatory methods. This study aimed to translate, culturally adapt and psychometrically evaluate the Italian SSC in patients with SLE, and to characterize its dimensionality. Methods: A cross-sectional study was conducted in 331 patients (301 with SLE, with or without antiphospholipid syndrome [APS]; 30 with primary APS as an exploratory subgroup). Items were recoded to a single 0–4 ordinal metric (0 = absent; 1–4 = burden). Analyses included exploratory factor analysis of polychoric correlations, within-sample ordinal confirmatory factor analysis, cross-validation, bifactor modeling and a sensitivity analysis excluding primary APS. Concurrent validity was assessed against the EQ-5D visual analog scale (EQ-VAS), GAD-7 and PHQ-9. Results: An exploratory 23-item short form, derived with loading-based retention rules, comprised five symptom clusters (pain/somatic–systemic, neuropsychological/mood, skin/treatment-related, appetite/weight, photosensitivity) and showed acceptable within-sample fit (CFI = 0.96; RMSEA = 0.055), but limited discriminant validity. Bifactor analysis showed a dominant general factor (ECV = 0.61; omega hierarchical = 0.85). The 38-item total score showed high internal consistency (α = 0.92) and correlated with EQ-VAS (ρ = −0.49), GAD-7 (ρ = 0.41) and PHQ-9 (ρ = 0.57); results were similar after excluding primary APS. Conclusions: The Italian SSC showed good internal consistency, content validity and concurrent validity, and should be considered an essentially unidimensional measure of symptom burden with five descriptive symptom clusters requiring independent confirmation. Its usefulness for longitudinal monitoring remains to be established.