Prevalence of undifferentiated inflammatory arthropathy in patients with Hashimoto's thyroiditis in an endocrinology clinic

Aim Rheumatic manifestations are common in patients with Hashimoto's thyroiditis (HT). Since previous reports on the prevalence of arthritis in this disease may have a rheumatology referral bias, we sought to establish the prevalence of undifferentiated inflammatory arthropathy (UIA) in unselected HT patients as seen in an endocrinology clinic. Methods Cross‐sectional study of 92 consecutive HT patients and no definite rheumatic disease from the Endocrinology Division, Hospital Universitario de Caracas diagnosed by the presence of anti‐thyroid peroxidase antibodies (n = 68) or typical ultrasonographic findings (n = 24). Undifferentiated inflammatory arthropathy was defined as combination of morning stiffness and joint pain with ≥2 characteristics of inflammatory joint pain. The study was revised and approved by the Ethics Committee of our hospital and all patients signed an informed consent form. Results Twenty‐three patients (25%; 95% CI 16‐34) met the criteria for UIA. Joints most commonly affected were the knees, hands and ankles and the most common pattern was oligoarticular (82.6%). In the multivariate analysis, variables associated to the presence of UIA were the presence of myalgia (odds ratio [OR] = 19.41; 95% CI = 2.38‐158.38) and Raynaud's phenomenon (OR = 4.32; 95% CI = 1.01‐18.60). No association was found with demographics, duration of disease, comorbidities or thyroid function status. Conclusions Almost 1 in 4 patients with HT had no definite rheumatic disease present with UIA. An early identification of concurrent arthritis in HT patients is necessary for thorough differential diagnosis and prompt treatment initiation to halt potential joint damage and disability.