Dysthyroidism in dermato/polymyositis patients: A case‐control study

Background Dermatomyositis (DM) and polymyositis (PM) are two rare autoimmune disorders occasionally described with dysthyroidism; however, no solid evidence still proves such an association. Aim To evaluate the prevalence of dysthyroidism among DM/PM patients. Design and setting A nation‐wide case‐control study was conducted. Methods From the Clalit Health Services health records database, we extracted 2085 (DM = 1475 (70.7%), PM = 610 (29.3%)) PM/DM cases and 10 193 sex‐age matched controls in the period 2000‐2018. Both univariate and multivariate analyses were performed to evaluate the link dysthyroidism and PM/DM. Survival analysis was also performed. Results The rate of hyperthyroidism was significantly ( P  = .0097) higher in cases (n = 40, 1.9%) with respect to controls (n = 123, 1.2%). Similarly, the rate of hypothyroidism was significantly ( P  < .0001) associated with cases (n = 234, 11.2%) when compared to controls (n = 853, 8.4%). At the multivariate logistic regression analysis, both DM (OR 1.31 [95%CI 1.07‐1.60], P  = .0087) and PM (OR 1.54 [95%CI 1.21‐1.95], P  = .004) were significantly associated with hypothyroidism, whereas DM (OR 1.70 [95%CI 1.10‐2.61], P  = .0165) but not PM (OR 1.45 [0.83‐2.55], P  = .1947) was found to be associated with hyperthyroidism. Subjects with PM and positive for anti‐Sjögren's syndrome‐related antigen A (SSA) auto‐antibody displayed a significant risk of developing hyperthyroidism (OR 5.85 [95%CI 1.02‐33.74], P  = .0480), whereas individuals with DM and positive for antinuclear antibody (ANA) had a higher risk of developing hyperthyroidism (OR 2.65 [95%CI 1.00‐7.03], P  = .0498). Conclusions Physicians treating PM/DM patients should consider screening for thyroid dysfunction on a regular basis.