Association between idiopathic retroperitoneal fibrosis and autoimmune thyroiditis: A case–control study

BackgroundIdiopathic retroperitoneal fibrosis (IRF) is a rare disease often associated with autoimmune disorders. Whether IRF is associated with Hashimoto's thyroiditis (HT) is poorly understood and only addressed by case-reports. We evaluated the prevalence of HT in a large IRF cohort and in matched controls.MethodsWe studied 73 consecutive patients with new-onset IRF and 71 controls. The association between HT and IRF was cross-sectionally evaluated in a referral center. Longitudinally, thyroid function tests were also performed. Serum concentrations of FT4, TSH, and anti-thyroperoxidase antibodies (AbTPO) were evaluated together with thyroid ultrasound (US). Lymphocytic infiltrates were characterized in thyroid nodule fine needle aspirates (FNAB). In patients undergoing thyroidectomy, thyroid histology was also reviewed.ResultsA higher prevalence of AbTPO positivity (P < 0.03) and US findings suggestive of autoimmune thyroiditis (US-AIT) (P < 0.0001) were found in IRF patients compared to controls. In the logistic regression analysis, the risk of AbTPO-diagnosed HT and that of US-AIT was significantly higher in IRF patients than in controls (ORs, 3.56, 95% CI 1.48–8.59, P = 0.004 and 4.74, 95% C.I., 2.34–9.61, P < 0.0001 in AbTPO-diagnosed HT and US-AIT, respectively). Thyroid histology in IRF patients showed either classical or the fibrous variant of HT. At the end of the follow-up (median, 45 and 36 months in patients and controls, respectively), 25% of IRF patients and 3% of controls were receiving l-thyroxine.ConclusionsIRF patients have a higher risk of HT compared to controls. Thyroid function should be monitored in patients with IRF.