Predictors of Shoulder Pathology in Rheumatoid Arthritis: A Cross-Sectional Study

TL;DR

This study identifies blood and metabolic factors linked to shoulder pain and disability in rheumatoid arthritis patients.

Contribution

The study identifies novel clinical and laboratory predictors of shoulder pathology and disability in rheumatoid arthritis.

Findings

Lower hemoglobin and higher platelet count predict abnormal ultrasound findings in RA patients.

Elevated ESR and vitamin D deficiency are associated with shoulder pathology.

Metabolic factors like blood sugar and thyroid hormone levels affect shoulder disability scores.

Abstract

Background: Shoulder pain is a frequent but under‑recognized manifestation of rheumatoid arthritis (RA), contributing substantially to disability and impaired quality of life. High‑resolution musculoskeletal ultrasound (HRUS) offers sensitive detection of structural abnormalities, while the Shoulder Pain and Disability Index (SPADI) provides patient‑reported assessment of pain and function. However, the clinical and laboratory predictors of shoulder pathology and disability in RA remain incompletely defined.

Methods: In this cross‑sectional study, 105 RA patients presenting with shoulder pain were enrolled. All participants underwent HRUS evaluation of the affected shoulder(s) and completed the SPADI questionnaire. Baseline demographic and laboratory parameters were recorded. Binary logistic regression was used to identify predictors of abnormal HRUS findings and seropositivity, while linear regression analyses examined associations with SPADI total (SPADI‑T), pain (SPADI‑P), and disability (SPADI‑D) scores.

Results: Abnormal HRUS findings were present in 69 patients (65.7%). Logistic regression identified lower Hb (p=0.006, OR=0.01) and higher platelet (PLT) count (p=0.016, OR=1.16) as significant predictors of abnormal HRUS findings, with erythrocyte sedimentation rate (ESR) (p=0.010) and vitamin D deficiency (p=0.050) approaching significance. Higher ESR was also correlated with higher CRP. Linear regression demonstrated that longer disease duration, lower Hb, higher PLT count, elevated random blood sugar, and higher thyroid-stimulating hormone were predictors of worse SPADI‑T scores (R²=54.4%).

Conclusion: Shoulder pathology in RA is multifactorial, with anemia, thrombocytosis, systemic inflammation, metabolic derangements, and vitamin D deficiency contributing to pain and disability. HRUS abnormalities are strongly linked to hematologic and metabolic markers, while functional impairment is influenced by both inflammatory and endocrine factors.

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