Recurrent Orbital Myositis Mimicking Sixth Nerve Palsy: Diagnosis with MR Imaging

Abstract

SUMMARY:We present a case with recurrent orbital myositis sequentially affecting both lateral rectus muscles separately. In the first episode, the absence of the required symptoms for the diagnosis of orbital myositis led to the erroneous diagnosis of sixth nerve palsy. Eventually, the correct diagnosis was established with cerebral MR imaging. Orbital myositis should be included in the differential diagnosis of what appears clinically to be abducens palsy, and MR imaging with a focus on the orbita is mandatory in such patients.

Cutting the edge of idiopathic recurrent orbital myositis

“…Pollard [4] diagnosed neuroradiologically the IOM of 7 children, showing isolated acute painful lateral rectus muscle palsy similarly to Fischer et al adult case [5] who mimicked a 6 th nerve affection. The differential diagnosis of IOM include focal myasthenia gravis, pathologic processes of the base of the skull, mitochondrial disorders as progressive external ophthalmoplegia, sarcoidosis, ophthalmoplegic migraine, lupus erythematosus, Wegener's disease, multiple post-infectious combinations of cranial nerve involvement [1][2][3][4][5][6][7][8][9][10]. The final diagnosis of IOM can be challenging due to difficulty in obtaining affected tissues or in using EMG as diagnostic tool [2,3,5,6].…”

“…CT and MRI scans in our cases showed enlargement, altered signal of suspected muscles, in absence of signs of orbital pseudotumor [2][3][4][5][6][7]. Multiple muscles were affected in their entirety, from origin to insertion differing from most common causes of orbital inflammation, such as the thyroid ophthalmopathy, which predilects muscle's belly [1,2,[4][5][6][7]. Normal appearance of cavernous sinus, superior orbital fissure, intact sensation over trigeminal nerve distribution excluded a Tolosa-Hunt syndrome or other invading granulomatous processes [7].…”

“…The differential diagnosis of IOM include focal myasthenia gravis, pathologic processes of the base of the skull, mitochondrial disorders as progressive external ophthalmoplegia, sarcoidosis, ophthalmoplegic migraine, lupus erythematosus, Wegener's disease, multiple post-infectious combinations of cranial nerve involvement [1][2][3][4][5][6][7][8][9][10]. The final diagnosis of IOM can be challenging due to difficulty in obtaining affected tissues or in using EMG as diagnostic tool [2,3,5,6]. Lee et al patient [10] was thought to have cluster headache 6 years before MRI demonstrated thickened superior rectus muscle; Pagès et al case [3] presented sudden lateral rectus palsy 2 years before CT scan revealed fusiform hypertrophy of affected muscle.…”

“…Recurrences occasionally involve different muscles of the controlateral eye [1][2][3]6]. Diagnosis is usually made clinically on account of persisting, often recurrent orbital pain and signs of inflammation [1][2][3][4][5][6][7][8]. The purpose of this report is to present a case series of IOM possibly providing a frame work for the diagnosis.…”

“…The spectrum of orbital inflammations ranges from specific diseases as connective tissue disorders, thyroid ophthalmopathy to non specific disorders involving orbital structures [1][2][3][4][5][6][7][8]. Idiopathic orbital myositis (IOM) may a localized process, involving primarily extraocular muscles without systemic involvement or it can be associated with systemic diseases [1][2][3][4][5][6][7][8].…”