Orbital myositis is a rare, inflammatory, noninfectious disorder that affects the ocular muscles. It is presumed to be an autoimmune disorder.
The condition affects women twice as often as men and typically presents in early adulthood.
Clinical features of orbital myositis:
(1) The onset is usually acute or subacute.
(2) The patient presents with diplopia with or without ptosis.
(3) There is a painful ophthalmoplegia.
(4) There is often conjunctival injection and/or chemosis.
(5) There is usually preservation of visual acuity.
(6) There are characteristic changes on orbital MRI (see below).
(7) The patient often shows a rapid response to corticosteroid therapy but refractory cases occur.
There are 2 clinical forms based on the severity of the inflammation:
(1) limited oligosymptomatic ocular myositis (LOOM)
(2) severe exophthalmic ocular myositis (SEOM) with chemosis, pupillitis and proptosis
(1) The changes can be seen in T2-weighted or contrast-enhanced T1 with fat suppression
(2) There is thickening of the affected extra-ocular muscle (EOM) at the myotendinous junction with contrast enhancement of adjacent fat
The diagnosis requires exclusion of other causes of ophthalmoplegia.
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Specialty: Ophthalmology, Immunology/Rheumatology