Thyroid volume and severity of Graves' orbitopathy.

Background: Graves' orbitopathy (GO) is thought to be related to one or more autoantigens present in the thyroid and in orbital tissues. Although this may not imply a quantitative relation between thyroid antigens and degree of GO, which in turn is a risk factor for a more pronounced GO, we postulated that the severity of GO may parallel the amount of thyroid tissue, namely, the size of the thyroid gland. This hypothesis is also based on the observation that patients with Graves' disease presenting with large goiters tend to have more severe hyperthyroidism. Thus, we evaluated retrospectively whether there is a correlation between the degree of GO at its first observation and, among other parameters, the thyroid volume.

Methods: Eighty-six consecutive patients with untreated GO lasting for no longer than 24 months underwent an endocrinological and an ophthalmological evaluation, the latter including: exophthalmometry, eyelid width, clinical activity score (CAS), diplopia, and visual acuity. The overall degree of GO was ranked using the NOSPECS score as well as a modification of the NOSPECS score. The following parameters were considered for correlations: time since GO appearance, time since detection of hyperthyroidism, FT3, anti-thyrotropin receptor antibodies, thyroid volume, and cigarette-years.

Results: Thyroid volume, but not the other parameters, correlated significantly by simple regression with exophthalmometry (p=0.02) and CAS (p=0.02). The standard NOSPECS score correlated with FT3 (p=0.05), thyroid volume (p=0.02), and cigarette-years (p=0.03), by simple, but not by multiple regression analysis. The modified NOSPECS score correlated with thyroid volume (p=0.007) and cigarette-years (p=0.04) by simple regression, and with thyroid volume also by multiple regression analysis (p=0.05).

Conclusions: Thyroid volume correlates with the severity of GO at its first observation, especially with exophthalmometry and CAS. The finding is in line with a possible pathogenetic role of antigens shared by the thyroid and orbital tissues. Nevertheless, other mechanisms may explain this observation, including an overall more reactive immune system in patients with a large goiter, resulting in more severe thyroid and eye disease, regardless of the nature of the autoantigen, or whether it is shared by the thyroid and the orbit.