[Orbital myositis, a cause of pediatric painful ophthalmoplegia].

Introduction: Orbital myositis (OM) is a serious inflammation of extraocular muscles with unknown etiology. Pe diatric presentation is rare and often affects more than one individual in a family, suggesting a genetic predisposition.

Objective: To describe a pediatric case of orbital myositis, its clinical characteristics, and the usefulness of MRI for confirming the diagnosis.

Clinical case: A 13-year-old female patient presenting with acute headache, right periorbital pain, exacerbated by eye movements, and blurred vision. We ruled out thyrotoxic myopathy, infectious diseases, autoimmunity, and malignancy. An MRI showed right medial rectus muscle myositis and no evidence of optic neuritis. She was treated with intravenous systemic glucocorticoids followed by oral steroids with complete clinical resolution.

Conclusions: OM has unknown etiology and can present a malignant course. Due to its unspecific clinical presentation, a comprehensive differential diagnosis should be made and it should consider performing MRI. Early treatment avoids permanent damage of extraocular muscles.