Differences between Graves’ Disease and Thyroid Eye Disease
Notable Differences in Symptoms and Diagnostic Criteria
In Graves’ disease, patients have hyperthyroidism, which is readily suspected when the patient presents with typical symptoms such as palpitations, weight loss, heat intolerance, tremor, and others. Widely available blood tests will confirm a low TSH and high thyroid hormone levels confirming the diagnosis. Hyperthyroidism of any cause can cause mild eye symptoms: the parasympathetic system is hyperactive and increases the tone of the levator palpebrae superioris muscle. This phenomenon results in functional retraction of the upper eye lid (lid lag) and in a delay in the eye lid following the iris in the downward gaze (von Graefe’s sign).¹ These changes result in the typical “stare” seen in many hyperthyroid patients, but do not necessarily signal thyroid eye disease, and will resolve with resolution of the hyperthyroidism.
The presentation of TED includes fixed eye lid retraction, inflammatory in nature, but also several other important findings such as eyelid edema and erythema, conjunctival injection and chemosis, proptosis and diplopia. In most cases, the diagnosis of TED is made on clinical grounds. TSH receptor antibodies are always present in hyperthyroid Graves’ disease, with or without TED.²
TED without Graves’ Disease
TED almost always occurs in the setting of Graves’ hyperthyroidism. Other forms of hyperthyroidism such as toxic multinodular goiter or toxic adenomas do not carry an increased risk of TED. However, in about 15 % of cases TED occurs in hypothyroid or euthyroid patients.³ The diagnosis may be delayed and more difficult in these cases, which also tend to be more often monolateral. In these cases, the diagnosis is based on the demonstration of positive TSH receptor antibodies. Imaging is also useful in unclear cases. In TED, orbital CT scans can show a typical pattern of extrinsic muscle involvement, with swelling of the muscle bellies and sparing of the tendons.
Graves’ Disease Treatment and TED Risk
Radioactive iodine is an excellent treatment for Graves’ hyperthyroidism. Unfortunately, it has become clear that it may also increase the risk of new TED, or worsen pre-existing TED.⁴˒⁵ It is very important that patients selecting radioactive iodine as treatment for their hyperthyroidism are adequately counseled on this risk, to allow for informed decisions.
An oral course of moderate dose glucocorticoids can prevent exacerbations of TED after radioactive iodine treatment,⁴ and should be considered in all patients with preexisting TED undergoing this treatment. It remains unknown whether novel agents used for TED can also help in this setting. No matter what treatment is chosen for hyperthyroidism, rapid control of hyperthyroidism and avoidance of iatrogenic hypothyroidism are necessary, as both can cause worsening of TED.⁵
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