Isthmin-1 as a Biomarker of Disease Activity in Rheumatoid Arthritis: Correlation With Musculoskeletal Ultrasound Findings

Rheumatoid arthritis is a chronic autoimmune disease characterized by persistent synovitis, pannus formation, and bone erosion leading to joint damage and functional impairment . It manifests as a symmetrical polyarthritis predominantly affecting the small joints of the hands, the earliest and most severely affected site in RA. A total of 94% of the patients suffered from at least one hand or wrist symptom after 2-4 years of disease duration. The most frequently described symptoms were pain, stiffness of the hand, muscle weakness, paresthesia, and a limited fist, which significantly impair their daily hand function. Current monitoring tools, including ESR, CRP, and DAS-28, lack sensitivity for subclinical synovitis. These limitations underscore the need for novel biomarkers integrating systemic inflammatory activity with joint pathology and functional status.

Isthmin-1 (ISM1), a multifunctional adipokine that suppresses NF-κB pathway, thereby reducing pro-inflammatory cytokine production and promoting tissue repair . This mechanism holds relevance in RA, where aberrant NF-κB activation drives synovitis and Th17-mediated immune responses . Its observed reduction in active RA signifies a loss of endogenous anti-inflammatory counter-regulation, establishing ISM1 as a promising biomarker for disease activity monitoring .

Musculoskeletal ultrasound (MSUS) provides superior sensitivity compared to physical examination for detecting synovitis (. MSUS findings correlate with structural damage and functional decline, making it a valuable tool for monitoring disease impact on hand joints . This study investigates correlations between serum ISM1 levels, MSUS findings, and hand function to identify biological links for novel RA therapies that preserve joint function and enhance quality of life.

Inclusion criteria

-Adult patients (≥18 years old) clinically diagnosed with rheumatoid arthritis according to the 2010 ACR/EULAR classification criteria.

Exclusion criteria

• Patients less than 18 years old.
• Patients with other autoimmune diseases.
• Participants with active infections, malignancies or diabetes.
• Recent hand surgery, trauma, deformity and neurological conditions affecting hand function