Background Orbital myositis (or idiopathic orbital myositis) is an inflammatory process affecting extraocular muscles.It is essential to distinguish it from other inflammatory conditions affecting the orbit including (but not limited to) Thyroid associated ophthalmopathy, vasculitides including GPA, Sjogrens syndrome, sarcoidosis.At intial presentation it might be confused with other disease processes including infections, malignancies, congenital lesions (eg hemangioma), foreign body etc. For optimal management it is essential to differentiate it from these entities. We aim to help in understanding this disease by sharing our experience in diagnosis and management of patients presenting with this condition.

Objectives We aim to describe the salient features including clinical presentation, laboratory, imaging and histopathologic findings and treatment in patients seen in a tertiary care pediatric rheumatology center with a diagnosis of orbital myositis.

Methods Retrospective chart review was performed in this series of patients presenting with inflammatory lesions of the orbit/s involving extraocular muscles, between December 2004 and August 2014

Results 9 patients with median age of 14 years (with range 6yrs – 16yrs) at the time of initial diagnosis were identified. Duration of symptoms at the time of presentation ranged from a few weeks (2 weeks) to several years (2 years). Most common presenting symptom was orbital pain in all the patients followed by headache and diplopia in 78% and 56% patients respectively. Motility restriction was fairly common on exam seen in 67% patients. Increased intraocular pressure was seen in 3 patients. Bilaterality was seen in 8 cases (89%). Decreased visual acuity was seen in 1 patient due to optic nerve involvement. Laboratory workup did not reveal any specific characteristics and only 1 patient had positive anti thyroid antibodies in absence of any clinical signs/symptoms suggestive for thyroid disease along with normal thyroid function tests. One patient over course of first year after initial presentation developed inflammatory bowel disease.

Imaging was obtained in all patients with orbital MRI (n=7), orbital CT scan (n=4), both MRI and CT scan (n=2). Biopsy of extra ocular muscles was obtained in one patient with evidence of mild chronic inflammatory infiltrate.

All cases were steroid responsive, although majority required the addition of a steroid sparing agent due disease recurrence or steroid dependence. Methotrexate was the most commonly used initial DMARD in these cases with good response. One patient had recalcitrant disease despite therapy with corticosteroids, methotrexate and Infliximab and is currently being treated with Rituximab with good initial response to therapy.

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Conclusions Idiopathic orbital myositis is a rare inflammatory disorder in the pediatric population. What makes the diagnosis even more difficult is the vast differential diagnosis. Our case series is one of the largest series of patients diagnosed and followed over time with this condition. It is fairly steroid responsive, although recurrence is common and warrants further treatment. First line treatment with methotrexate is appropriate with good response in majority. Further biologic therapy is needed in resistant cases, although there are no set guidelines to direct management.

References

1. Semin Arthritis Rheum 2008 Feb;37(4):207-22. Epub 2007 Sep 4.Orbital inflammatory disease. Lutt JR, Lim LL, Phal PM, Rosenbaum JT.

Disclosure of Interest None declared