Idiopathic orbital myositis mimicking orbital cellulitis.

Idiopathic orbital myositis (IOM) is a subtype of orbital inflammatory disease characterized by primarily involving the extraocular muscle. The signs and symptoms of IOM may also be seen in such processes as orbital cellulitis, primary or metastatic orbital neoplasm, carotid-cavernous fistulae, arteriovenous malformations, cavernous sinus thrombosis, and thyroid eye disease, and because there is no pathognomonic sign, symptoms, laboratory test, or radiologic findings, its diagnosis is often provisional. In our case, diagnosis of IOM was more difficult because our patient presented with proptosis after alloplastic implant insertion in the blow-out fracture. After considering radiologic and physical findings, we concluded that cellulitis was more likely as initial diagnosis. To remove foreign body or pus, surgical exploration was done, but intraoperative findings did not show any pus or sign of infection but diffuse enlargement and swelling of inferior rectus muscle. The diagnosis was confirmed as IOM, and the patient was treated with systemic corticosteroid. Although proptosis after alloplastic insertion in blow-out fracture is usually a sign of cellulitis, this case illustrates that it may also occur in patients with IOM.