Orbital Myositis in Pediatric and Adult Patients: A Comparative Case Report and Review of the Literature.

Idiopathic orbital inflammatory disease (IOID) is a rare, noninfectious inflammatory disorder of the orbit and a diagnosis of exclusion. Orbital myositis, a subtype characterized by inflammation of one or more extraocular muscles, is uncommon in both children and adults and may mimic infectious, neoplastic, or systemic inflammatory conditions. We report two cases of orbital myositis in different age groups to highlight the variability in clinical presentation, diagnostic challenges, and management. An 11-year-old previously healthy girl presented with left periocular pain, eyelid edema, and conjunctival hyperemia. Initial treatment for presumed orbital cellulitis with oral and IV antibiotics failed, and the patient developed painful restriction of elevation and adduction. Computed tomography and MRI demonstrated enlargement of the left medial rectus muscle without sinus disease, abscess, or orbital mass. A 46-year-old previously healthy woman presented with headache, upper eyelid edema, binocular diplopia, and limitation of downgaze. MRI revealed enlargement of the left superior rectus muscle. In both cases, laboratory investigations excluded infectious, autoimmune, and systemic inflammatory etiologies. Prompt corticosteroid therapy resulted in rapid clinical improvement and complete resolution without recurrence. These cases illustrate the clinical spectrum of orbital myositis across different age groups. The pediatric patient initially mimicked orbital cellulitis, whereas the adult patient presented with painful ophthalmoplegia. Failure of presumed orbital cellulitis to improve with appropriate antibiotics, particularly in the absence of fever, sinusitis, or elevated inflammatory markers, should prompt consideration of orbital myositis. Characteristic imaging findings, including isolated extraocular muscle enlargement in the absence of sinus disease, abscess formation, or neoplasia, were crucial for diagnosis. Early recognition and prompt corticosteroid treatment generally result in excellent clinical outcomes, although biopsy and radiotherapy may be necessary in atypical or recurrent cases.