Skin Autofluorescence Assessment of Advanced Glycation End Products in Rheumatic Diseases

Inclusion Criteria: * Age between 18 and 75 years * Diagnosis of an inflammatory rheumatic disease (including rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, reactive arthritis, connective tissue diseases, Behçet disease, familial Mediterranean fever, or crystal arthropathies), confirmed by a rheumatologist * Healthy volunteers without a history of rheumatic or chronic inflammatory disease (for the control group) * Ability to undergo non-invasive skin autofluorescence measurement * Ability and willingness to provide written informed consent Exclusion Criteria: * Diagnosis of diabetes mellitus (type 1 or type 2) * Chronic kidney disease with estimated glomerular filtration rate (eGFR) \< 60 mL/min/1.73 m² * Active malignancy or history of malignancy within the past 5 years * Presence of acute infection or acute inflammatory condition at the time of assessment * Secondary causes of systemic inflammation unrelated to the underlying rheumatic disease (e.g., uncontrolled endocrine disorders, chronic liver disease) * Use of medications known to markedly affect AGE accumulation or skin autofluorescence measurements (e.g., recent high-dose systemic glucocorticoids) * Pregnancy or breastfeeding * Presence of significant skin conditions (e.g., extensive dermatitis, scars, tattoos, or burns) at the measurement site that may interfere with skin autofluorescence assessment * Inability to comply with study procedures or to provide informed consent