Skin fibrosis correlates with circulating thyrotropin levels in systemic sclerosis: translational association with Hashimoto’s thyroiditis

Systemic sclerosis (SSc) is a connective tissue disease, characterized by cutaneous and multi-organ fibrosis, and vascular abnormalities. Skin thickening is a characteristic feature of SSc and resembles myxedematous skin. Our aim was to correlate the degree of skin involvement in SSc patients with serum TSH levels, since TSH receptors are widely expressed in human tissues, including the skin. In this cross-sectional study, we enrolled 70 SSc patients, all females with a mean age of 47 ± 11 year. Thirty-five age- and sex-matched HT patients were recruited, as controls. Subjects under L-thyroxine therapy and/or with positive anti-TSH receptor antibodies were excluded. In all subjects, we measured serum TSH, FT4, and free tri-iodothyronine (FT3) levels. Skin thickness was evaluated using the modified Rodnan total skin score (mRSS). mRSS averaged 14 ± 9 for SSc and 4 ± 6 for HT patients. TSH levels positively correlated with skin scores in both SSc and HT patients groups. In SSc patients, FT3 and FT4 showed an inverse correlation with mRSS, while in HT only FT4 levels showed this inverse significance. When divided by cutaneous extent, SSc patients with diffuse disease form had higher TSH serum levels compared to those with the limited form; additionally, the correlations between TSH, FT4, and mRSS reached statistical significance. Our preliminary data clearly indicate that serum TSH is higher in SSc patients with more severe skin disease, and significantly correlate with the mRSS. Therefore, TSH could play a role in the development of cutaneous changes in SSc patients.