Background/Purpose:  While thymic alteration such as hyperplasia, cyst and neoplasia has been precisely studied particularly in myasthenia gravis [1], only a few small-scale studies have been reported in a part of systemic autoimmune diseases [2-4]. We conducted a large-scale cross-sectional analysis on prevalence of radiographic thymic alteration and its clinical association in various systemic autoimmune diseases.

Methods:  Consecutive and unbiased 500 patients who had visited at our service and had been evaluated by chest CT scan between January 2013 and December 2015 were enrolled. Thymus size and the radiographic pattern on high-resolution CT image were quantitatively interpreted. We defined hyperplasia as more than 13mm thickness and graded the patterns by four-point scale (grade 0-3) according to previous study [5,6]. Their association to clinical information was statistically analyzed.

Results:  Thymoma and thymic cyst were found in 3 (0.6%) and 1 (0.2%), respectively. After above cases and less than 30 year-old patients were excluded, 488 were served for following analysis. 78% were women and mean age was 63.0 ± 13.9 years old. These included 168 patients with rheumatoid arthritis (RA), 63 with systemic sclerosis (SSc), and 37 with primary Sjögren’s syndrome (pSS). Thymic hyperplasia was found in 90 (18%) overall. These included 41 (24%) with RA, 6 (10%) with SSc, and 7 (19%) with pSS. Remarkably, patients with granulated pattern (grade 1 and over) was more frequent (42%) as compared to undiagnosed controls. These included 78 (46%) patients for RA, 32 (51%) patients for SSc, and 17 (46%) for pSS. Regarding clinical association, when RA patients is classified by hyperplasia and granulated pattern, proportion of serum anti-cyclic citrullinated peptide antibody (ACPA)-positivity were significantly higher in alteration group compared to normal group (93% vs. 70% and 89% vs. 63%; P=0.004 and 0.0005, odds ratio=6.1 and 5.0). In addition, titer of ACPA was also positively correlated to both hyperplasia and granulated pattern (P=0.048 and 0.009).

Conclusion:  Thymic alteration was found in quite a few patients with various systemic autoimmune diseases. In RA patients, radiographic thymic alteration, especially granulated pattern significantly correlates to ACPA status and may reflect activation of germinal centers in the thymic medulla. References： [1] Clinic Rev Allerg Immunol 2016 Jun 6. [Epub ahead of print], [2] Semin Arthritis Rheum. 1998; 28:73-79, [3] Joint Bone Spine. 2013; 80:48-51, [4] Rheumatology(Oxford). 2014; 53:732-736, [5] Radiology. 2013; 268(1):245-253, [6] Eur Radiol. 2016; 26(1):15-24

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/prevalence-of-radiographic-thymic-alteration-and-its-clinical-association-in-systemic-autoimmune-diseases/