Increased frequency of euthyroid ophthalmopathy in patients with Graves' disease associated with myasthenia gravis

We previously showed that myasthenia gravis (MG) has a mild clinical expres sion when associated with autoimmune thyroid diseases (AITD). In the presen t study we have investigated the frequency of thyroid-associated ophthalmop athy (TAO) in patients with Graves' disease (GD) associated with MG as comp ared with GD patients without MG. A total of 418 patients with GD were stud ied, 31 with MC and 387 without MG. TAO was evaluated by physical examinati on, exophthalmometry, computerized tomography, and computerized visual fiel ds assessment. The overall prevalence of TAO was similar in GD patients wit h MG (61.2%) and in those without MG (56.4%). When the analysis was restric ted to CD patients with ocular MG, a greater frequency of TAO was found (84 .6%), compared with GD patients without MG or with GD patients with general ized MG, although the differences did not reach the statistical significanc e. GD patients with MG had a significantly greater prevalence (12.9%) of eu thyroid ophthalmopathy (clinically overt ophthalmopathy without previous an d/or current hyperthyroidism) than those without MG (3.1%; p = 0.003). The results suggest a preferential association between the ocular manifestation s of GD and MG, which may be due to immunological cross-reactivity against common autoimmune targets in the eye muscle as well as to a common genetic background.