Background/Purpose: Cystic Fibrosis (CF) is a common genetic mutation in Caucasian populations. Many patients have musculoskeletal complaints and 12% develop arthritis, including CF arthropathy (CFA), a poorly understood entity of episodic mono or polyarthritis, and other inflammatory arthropathies. Prior studies have been limited to small patient cohorts showing no clear association with disease severity or complications, or specific laboratory results. Thus, diagnostic criteria are not well defined and the pathogenesis remains unclear. The goal of this study was to compare disease characteristics and laboratory findings between patients with CF with and without arthritis from a large cohort.

Methods: Patients with CF seen at 2 tertiary care hospitals over a 6 year period were screened for musculoskeletal symptoms via questionnaire or referral. Patients with symptoms underwent a comprehensive evaluation including chart review, medical history and physical examination by a rheumatologist, laboratory testing and pulmonary function testing. Patients were diagnosed with arthritis if they had physician documented evidence of joint effusion, warmth, or limited range of motion. Age- and gender-matched control patients with CF without arthritis were also evaluated.  Comparisons between cases and controls were made by univariate and multivariate logistic regression analyses to identify independent markers of arthritis.

Results: The study cohort consists of 25 patients with CF and arthritis and 72 without arthritis. Demographic features were similar with no differences in the presence of disease complications (Table 1). Univariate analysis did find a higher percentage of rheumatoid factor (RF) positivity in patients with arthritis compared to patients without arthritis (18% vs. 3%, p = 0.04), with no other between group differences (Table 2). Regression analysis suggested this association held (p=0.05) after controlling for other markers of disease severity (age, IgG level, and FEV1).

Conclusion: In this largest cohort to date, patients with CF and arthritis were more likely to have a positive RF compared to patients without arthritis, suggesting that the pathophysiology may be related to accumulation of antigenic immune markers. There were no other differences, indicating that the etiology and spectrum of disease may vary and requires additional exploration, including genotype evaluation and longitudinal follow-up.

Table 1. Comparison of demographic features and disease complications between groups

Table 2. Comparison of laboratory features among groups

Data are mean (SD) unless otherwise indicated. IQR = interquartile range.