Systemic sclerosis patients are at higher risk of hyperthyroidism and have a worse survival than those without hyperthyroidism: A nationwide population‐based cohort study

BACKGROUND: A high prevalence of thyroid disorders has been reported in patients with autoimmune diseases. The link between hyperthyroidism and systemic sclerosis (SSc) has been relatively overlooked, and only a few studies utilizing small samples or case reports have been reported so far. OBJECTIVES: To investigate the association between SSc and hyperthyroidism. METHODS: We designed a case-control study utilizing the medical database of the Clalit Health Services. Chi-square and t tests were used for univariate analysis, and a logistic regression model was used for multivariate analysis. RESULTS: The study included 2,431 SSc patients and 12,710 age- and sex-matched controls. The mean age of the study population was 63.32 +/- 18.06 years (median 66 years), and female-to-male ratio was 4.5:1. Age (P < .0001, OR 1.03 [95% CI 1.02-1.04]), female sex (P = .0015, OR 1.86 [95% CI 1.27- 2.74]) and diagnosis of SSc (P = .0011, OR 1.81[95% CI 1.27-2.58]) were all independently associated with hyperthyroidism. Patients with SSc and hyperthyroidism had 1.54-fold increase of mortality rates during a mean follow-up of 17 years than SSc patients without hyperthyroidism, even though at the Cox multivariate survival analysis, only age (HR 1.06 [95% CI 1.06-1.07], P < .0001) and diagnosis of SSc (HR 2.35 [CI 2.06 to 2.69], P < .0001) resulted associated with a higher risk of mortality. CONCLUSIONS: Hyperthyroidism is highly prevalent among SSc patients and can negatively impact on their survival rates. Therefore, a pre-emptive screening may be warranted in all SSc patients. Further studies are needed to evaluate whether tight control and optimal treatment for hyperthyroidism may lead to a reduction of all-cause mortality in patients with SSc.