What we see is enlargement of the extraocular muscles that "spares" the myotendinous junction.
This is Thyroid Ophthalmopathy
- Usually occurs in patients with Grave's disease - but can be seen in any thyroid state
- Resolves in >90% of patients
- Most common cause of proptosis in adults
- Histology - inflammatory leukocytic infiltration with edema and deposition of mucopolysaccharides - leading to fibrosis, lipomatosis, fatty degeneration.
- Can compress optic nerve leading to optic neuropathy
- Can cause diplopia due to muscle entrapment
- Proptosis - can lead to corneal ulcers and conjunctival congestion
- Most frequently involves medial and inferior recti - IMSLow - Inferior, medial, superior, lateral; muscles >4 mm
- More frequent in women but more severe in men
- Expansion of orbital fat
- Upper and lower eyelid retraction
- Often bilateral and symmetric
- Painless
- TX - prednisone, radiotherapy, surgical decompression, thyroid surgery, I-131
- DDX - pseudotumor (painful, unilateral, involves tendons, inflammed fat, good response to steroids) [can be idiopathic, sarcoid, endocrine, focal infections, foreign bodies], cavernous hemangioma of the orbit, Histiocytosis X, cavernous sinus thrombosis, intraconal varices, lacrimal gland tumor and don't forget mets (usually osseous)
- Imaging - Ultrasound, CT (good bone imaging and shows all the features but has radiation), MRI
References: http://emedicine.medscape.com/article/383412-overview ; Neuroradiology Companion by Mauricio Castillo and Primer of Diagnostic Imaging by Weissleder et al.
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