To evaluate success rate and predictive factors for the success of botulinum toxin injection for the treatment of restrictive myopathy in thyroid-associated orbitopathy (TAO).

Twenty patients with restrictive myopathy of TAO entered the study.Abnormal thyroid function tests were not required for all patients to be accepted into the study.In each extraocular muscle, 25 units of Dysport were injected. The success rate, calculated at 2 years or the last follow-up before surgery, was defined as proportion of the cases with esotropia (ET) <10 prism diopters (PD), vertical deviation<5 PD, and no diplopia in primary position and downgaze for at least 1 year. Both univariateanalysis and multivariate logistic regressions were performed to identify the factors associated with success.

The procedure was successful in 11 cases (55%). In subgroup analysis, the procedure was successful in 8 patients (80%) of predominantly ET subgroup, 1 patient (12.5%) of predominantly HOT subgroup, and both patients (100%) of mixed subgroup. Four factors were significantly associated with the success: type of deviation (p=0.007), lower amounts of HOT (p=0.001) and ET (p=0.05), and lower degree of extorsion (p=0.01). In the multivariate logistic regression, only lower amount of HOT was significantly associated with the success (p=0.09, OR=1.36).

The injection of botulinum toxin can be an effective alternative for the treatment of the restrictive myopathy in TAO. The best candidates for injection of the toxin are patients with ET, smaller angle of horizontal and vertical deviations, and lower degree of extorsion.