Isolated Unilateral Ptosis Caused by Orbital Myositis Involving the Superior Rectus-Levator Muscle

Abstract

Purpose: To present a case of orbital myositis involving the levator palpebrae superioris/superior rectus muscle (LPS/SR) complex with isolated unilateral ptosis and preserved extraocular muscle function and to review of the literature.Case summary: A healthy, 54-year old man presented with acute right upper ptosis detected 3 hours before. His best-corrected visual acuity was 20/20 in both eyes. His margin-reflex distance 1 was -2 mm and +4 mm, and levator function was 11 mm and 14 mm in the right and left eyes respectively. There was no proptosis. He had full extraocular motility with no strabismus, and normal pupillary function. There was no improvement in ptosis with the ice test and 0.5% apraclonidine test. Orbital magnetic resonance imaging demonstrated thickening and enhancement of right LPS/SR complex. Consequently, we diagnosed him with orbital myositis involving the LPS/SR complex. We started treatment with corticosteroid and ptosis completely resolved after 1 month since onset.Conclusions: We report a case of orbital myositis who showed inflammation of the LPS/SR complex early in the disease course and allowed the preservation of normal SR function. Inflammation of the LPS/SR complex might affect the function of these muscles differently due to the differences in muscle mechanics. Although orbital myositis involving LPS/SR complex is rare, it should be considered as a differential diagnosis in patients with acute unilateral ptosis.