Painful acute esotropia as a presenting sign of presumed post-infectious orbital myositis in a child: a case report.

purposeTo describe a self-limited presentation of pediatric orbital myositis and discuss its implications for management. OBSERVATIONS: A previously healthy 9-year-old boy presented with acute painful diplopia and esotropia following a recent febrile upper respiratory tract infection and presumed viral conjunctivitis. Best-corrected visual acuity was 20/40 OD and 20/40 OS. Examination demonstrated an esotropia of 30 prism diopters (PD) at corrected distance and 35 PD at corrected near, bilateral abduction limitation (- 1), and localized temporal conjunctival injection over the lateral rectus insertions, with clinical features also suggestive of lacrimal gland involvement. Magnetic resonance imaging (MRI) of the orbits revealed bilateral enlargement and post-contrast enhancement of the lateral rectus muscles with mild tendon involvement and surrounding inflammatory changes, consistent with orbital myositis within the spectrum of idiopathic orbital inflammation (IOI). Dacryoadenitis was also suggested by imaging findings. Clear clinical improvement in pain, diplopia, and conjunctival injection was observed within 24 h of presentation, prior to initiation of any medical therapy. Although oral antibiotics and systemic corticosteroids were prescribed, corticosteroid therapy was not initiated due to intolerance. At three-month follow-up, the patient was orthophoric with full restoration of extraocular motility. CONCLUSIONS AND IMPORTANCE: This case illustrates a self-limited presentation of presumed post-infectious pediatric orbital myositis manifesting as painful acute esotropia, with bilateral lateral rectus muscle involvement and spontaneous recovery without corticosteroid therapy. Careful clinical and imaging assessment is essential to distinguish orbital myositis from neurogenic, accommodative, and infectious causes of acute esotropia in children. The reduced best-corrected visual acuity may reflect underlying refractive amblyopia and/or significant astigmatism and warrants continued monitoring. This report highlights an unusual but recognizable phenotype within the spectrum of pediatric idiopathic orbital inflammation and underscores the importance of comprehensive diagnostic evaluation and longer-term follow-up.