Myositis of an Extraocular Muscle, a Possible Drug Reaction: Histopathologic and Immunopathologic Analysis

A 58-year-old man presented with left-sided orbital inflammation, including chemosis and a lateral rectus abduction defect. Initially presumed to represent cellulitis, the condition responded poorly to oral and intravenous antibiotics. CT showed the epicenter of an infiltrate to involve the lateral rectus. The patient improved dramatically when oral prednisone was added. Lateral rectus biopsy displayed intramuscular polyclonal lymphoid infiltrates, rich with eosinophils. Complete resolution of the inflammatory process was confirmed by a follow-up CT. The presumptive diagnosis was idiopathic orbital myositis, an uncommon condition of unknown etiology. However, the patient had taken rosuvastatin, which has been rarely associated with diplopia and ophthalmoplegia, raising the question of whether this case was truly idiopathic.