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- Following along with the transcription
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Let’s start our USMLE Review with Hypothyroidism and Hyperthyroidism from the Gold Standard USMLE Foundations of Medicine Audio Review program.
Play USMLE Audio MP3 11 11 Summary of Classes Below
Begin 11 11 Summary of Classes Transcription
Student doctor please pause the tape and summarize the classes of eye changes in Graves’ disease as defined by the American Thyroid Association. Start with the pneumonic, remembering the classes and then give the sign in detail for each class.
- The eye signs of Graves’ disease as classified by the American Thyroid Association, include classes 0-6, from least to most eye involvement, with the first letter of each corresponding sign forming the pneumonic NO SPECS. Class 0-N for no signs or symptoms. Class 1 is O for only signs, no symptoms. The chief sign is spasm of the upper lids associated with active thyrotoxicosis. Class 2 is S for soft tissue involvement with periorbital edema and conjunctival redness, congestion and swelling, also called Chemosis. Class 3 is P for proptosis, where the distance from the orbital ridge to the anterior cornea is measured using a hertel exophthalmometer. Class 4-E for extraocular muscles involved are the inferior rectus limiting upward gaze and the medial rectus impairing lateral gaze. Class 5-C for corneal involvement is marked by keratitis. And class 6-S is for site loss due to impairment of the optic nerve.
Let’s look briefly at the mechanics behind a few of the eye conditions mentioned. Thyroid ophthalmopathy involves an acute inflammatory reaction that stems from infiltration of two substances into the extraocular muscles.
What are these substances?
- Thyroid ophthalmopathy is due to infiltration of lymphocytes and edema fluid into the extraocular muscles.
What is the orbit in the eye?
- The orbit is the bony cavity containing the eyeball and its anexa and is made up of parts of seven bones.
And what occurs in this closed cavity to cause proptosis of the globe?
- Swelling of the extraocular muscles within the orbit causes proptosis of the globe.
And the resulting impairment of muscle movement results in which sight abnormality?
- Diplopia or double vision.
Which two diagnostic tests can be used to demonstrate ocular muscle enlargement?
- Orbital CT scan or MRI will reveal ocular muscle enlargement.
When muscle swelling occurs posteriorly toward the apex of the orbital cone, what may occur to cause loss of vision?
- Compression of the optic nerve may cause loss of vision.
Student doctor please pause the tape and summarize the mechanics behind the occurrence of thyroid ophthalmopathy, proptosis of the globe, diplopia and vision loss as can occur with eye changes in Graves’ disease.
- Thyroid ophthalmopathy in Graves’ disease is due to infiltration of the extraocular muscles with lymphocytes and edema fluid in an acute inflammatory reaction. Swelling of extraocular muscles within the orbit causes proptosis of the globe and impaired muscle movement may cause diplopia, double vision. When ocular muscle swelling occurs posteriorly toward the apex of the orbital cone, the optic nerve is compressed possibly causing loss of vision.
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