Isolated lateral rectus myositis as a manifestation of idiopathic orbital inflammation

We report the case of of a patient with isolated, acute, monolateral and monomuscular lateral rectus myositis as a manifestation of a localized, nonspecific, idiopathic orbital inflammation.

A 25-year-old man presented to our clinic with a painful right eye and associated double vision on right gaze due to a limitation of abduction. Conjunctival hyperemia was observed in the area of the right lateral muscle insertion. A slight axial proptosis of the right eye was evident. On axial CT scans a fusiform enlargement of the right lateral rectus muscle including a thickened anterior tendon at its insertion was recorded. A thorough systemic and laboratory investigation showed neither any further abnormal findings nor any systemic disease.

A monocular, monomuscular myositis as a clinical manifestation of idiopathic orbital inflammation was diagnosed by the clinical findings and imaging with orbital CT/MRI scans. By appropriate treatment with oral steroids slowly tapered over weeks, symptoms and signs showed full remission without any complications. Clinical improvement was observed within a few days after the beginning of steroid administration.

Isolated lateral rectus myositis can be a manifestation of idiopathic orbital inflammation. Diagnosis is made by the clinical presentation and imaging with orbital MRI/CT-scans. Other local or systemic inflammatory, endocrine or neoplastic diseases must be ruled out.