Patterns of recurrence in idiopathic orbital myositis.

Purpose: To characterise patterns of disease recurrence in idiopathic orbital myositis (IOM).

Methods: Multi-centre retrospective longitudinal study of IOM patients. Serial imaging was also analysed. Patients with incomplete clinical records and specific orbital myositis (e.g. thyroid-associated ophthalmopathy) were excluded.

Results: Thirty-three patients (Female: 18, mean age: 40.8 ± 16.8-years-old) presenting between 2001 and 2023. Twelve (36.4%) patients had disease recurrence. There was no difference between age or sex predilection of patients with and without recurrence (P = 0.107 and 0.469, respectively). There was no association between patients presenting with multiple EOM involvement, unilateral disease, anterior tendon sparing or lacrimal gland involvement with recurrence (P = 0.328, 1.0, 0.630 and 0.686, respectively). Recurrence with single EOM involvement occurred in eight (66.7%) patients, and ten (83.3%) patients had recurrence involving different EOM(s) than on initial presentation. Seven (58.3%) patients had metachronous contralateral orbital involvement and one (8.3%) had simultaneous bilateral involvement. There was no association between age, sex, patients presenting initially with single EOM or lacrimal gland involvement with the development of contralateral orbital myositis (i.e. metachronous bilateral disease) (P = 0.777, 0.491, 0.109, and 0.236, respectively). Of the patients with a single acute episode, two (9.5%) patients experienced residual ocular symptoms, compared to four (33.3%) patients with recurrent disease (P = 0.159).

Conclusion: This study summarises the patterns of recurrence in IOM. Recurrence was not associated with age, sex, multiple EOM involvement, bilateral disease, tendon-sparing or lacrimal gland involvement. Recurrence was observed in a heterogenous sample of patients and may frequently develop contralateral disease or involve different EOMs (i.e. 'migratory' disease).