Inferior oblique myositis presenting as superior oblique muscle palsy.

A 14-year-old girl presented with progressive vertical strabismus simulating superior oblique muscle palsy. However, because of the presence of limitation of infraduction, computed tomography was done; it showed a large mass in the region of the right inferior oblique muscle. A biopsy specimen of the enlarged muscle showed mainly degenerative and some regenerative changes. The diagnosis was orbital myositis, which should be considered in the differential diagnosis of strabismus, especially if the clinical findings are atypical of strabismus.