Idiopathic orbital myositis is considered as a subgroup of
idiopathic orbital inflammatory disease. It is a non-infectious
inflammatory disorder primarily affecting the extraocular muscles
and causes various eye symptoms including pain, diplopia and
limitation of extraocular movement. Cases of isolated ptosis
by idiopathic orbital myositis have been very rarely described in
the literature. We report a patient who developed unilateral
painless ptosis caused by idiopathic orbital myositis. A 52-year-
old man presented with drooping of the right eyelid for 3 days.
There was no history of headache, double vision or any other
complaints. Neurological examination revealed right ptosis
without pupil and extraocular muscles involvement. Repetitive
nerve stimulation test was normal. Ptosis did not improve after
the neostigmine injection. Magnetic resonance imaging scan showed
asymmetric enlargement of right superior rectus/levator palpebrae
superioris muscle complex and medial rectus muscle. Ptosis
resolved dramatically after oral corticosteroid therapy. Isolated
unilateral ptosis can be caused by various etiologies. Idiopathic
orbital myositis should be considered in the differential
diagnosis of ptosis.

KEYWORDS : Orbital myositis, Blepharoptosis, Oculomotor muscles