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Editor,—A 46 year old woman presented with a 3 week history of discomfort, swelling, and drooping of her right upper lid. Recently she had developed rheumatoid arthritis but was otherwise fit and well. On examination her right visual acuity was 6/4 unaided, there was a complete right ptosis with very poor levator function, and mild periorbital swelling (Fig 1). Eye movements were full and the remainder of the ocular examination was normal. A computed tomograph (CT) scan showed isolated enlargement of the right superior rectus/levator muscle complex (Fig2).
Three weeks later her symptoms had improved. A 3 mm ptosis remained and the levator function had increased to 7 mm. There was lid lag on downgaze (Fig 3) suggesting both abnormal contraction and relaxation of the levator muscle. The ptosis gradually resolved over the next 4 weeks and the levator function returned to normal. It has not recurred.
Orbital myositis is an idiopathic inflammatory condition that affects the extraocular muscles. It may occur with a number of systemic conditions including rheumatoid arthritis.1 Ptosis in orbital myositis is quite common.1-4 The ptosis may result from orbital oedema secondary to inflammation or from direct involvement of the levator muscle with myositis. It is mentioned as a sign in several reports but there are no examination details such as the levator function, the degree of ptosis, or lid lag on downgaze to help establish the cause.1-3 Similarly, enlargement of the superior rectus/levator complex on CT, magnetic resonance imaging, or ultrasound is noted in some cases without any details of a ptosis.2 3 5
Our case had isolated involvement of the levator muscle. To our knowledge this has not been reported before. Isolated involvement of other single extraocular muscles is common. It occurred in 68% of the 75 cases reported by Siatkowski et al, usually the lateral or medial rectus.5 Isolated involvement of the oblique muscles also occurs.6
Siatkowski et al reviewed 75 patients with orbital myositis.5 They found a changing pattern of function in the extraocular muscles affected over the course of the disease. In the first 10 days the extraocular muscle function was normal. At 11–14 days there was a paretic phase. At 17–24 days there was a restrictive or mixed phase which partially or completely resolves. Our patient with isolated myositis of the levator muscle had a very similar course with the levator being almost completely paretic at the first visit. Three weeks later there was a mixed pattern of paresis and restriction with reduced levator function and lid lag on down gaze. A month after that it had completely resolved.
Orbital myositis should be considered in the differential diagnosis of acquired ptosis even if extraocular movements are full. We hope that the features of the ptosis will be reported in other cases to find out if the ptosis is the result of oedema or if the levator is affected by myositis.
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