To present a rare case of idiopathic orbital myositis involving levator palpebrae superioris.

A 27-year-old male presented with a 1-week history of redness, discomfort, swelling, and drooping of his left upper eyelid. A computed tomography scan showed isolated enlargement of the right superior rectus/levator muscle complex. On examination, there was a left blepharoptosis, although eye movements were normal. The authors treated the patient with 3rd-generation cephalosporin; however, after 3 days, the symptoms did not improve. Subsequently, the patient was diagnosed with idiopathic orbital myositis and treated with oral corticosteroids for 1 month; the symptoms gradually resolved.

Idiopathic orbital myositis is a subtype of nonspecific orbital inflammation primarily involving the extraocular muscles. Although the exact cause of orbital myositis is unknown, an immune-mediated pathophysiologic mechanism appears to be one of the causes. Medial rectus myositis is the most common, and isolated levator muscle myositis is very rare. The authors of the present study reported a case of orbital myositis involving the levator palpebrae superioris which should be considered a differential diagnosis of blepharoptosis with eyelid swelling.