Orbital Pseudotumor

Idiopathic orbital pseudotumor may affect orbital structures diffusely or focally. In orbital myositis, the disease affects one or more extraocular muscles. Secondary causes include SLE, sarcoid, Crohn's, Whipple's, lyme, Wegener's , or paraneoplastic. Mean age of occurence is 40. Usually a single muscle is involved, often a medial rectus causing limited abduction of the eye, mimicking a sixth nerve palsy. CT should be as good as MRI.

Differential diagnosis from Graves' disease is helped by MRI. Orbital myositis involves the tendon insertions, Graves' does not; orbital myositis has an acute painful onset whereas Graves' disease has a subacute painless presentation; patients typically respond quickly and dramatically to steroids, 100 mg per day for two weeks with a slow taper thereafter. Half of the patients may recur, requiring repeat treatment, other drugs or radiation.