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In the October 2002 issue of the Annals Nabili and colleagues described a case of orbital myositis (OM) associated with rheumatoid arthritis and suggested that the major differential diagnosis was thyroid ophthalmopathy.1
The mechanical component of orbital involvement in Graves’ disease (GD) can produce diplopia (5–10%), proptosis, chemosis, scleral injections, and retrobulbar pressure or pain, whereas eyelid lag or retraction and stare are caused by the spastic component (in some cases lid retraction can be obscured by periorbital oedema). The extraocular muscles most commonly affected are the medial and inferior rectus muscles.
The authors suggested characteristics which would distinguish the two conditions, and among these they included the systemic manifestations of GD.
GD should be seen as a systemic disease with various combinations of hyperthyroid goitre, ophthalmopathy, and dermopathy. Current pathogenetic theory shows that ophthalmopathy itself is a direct, independent manifestation of autoimmunity, caused by autoreactivity to the thyrotropin receptor expressed by the preadipocyte subpopulation of orbital fibroblasts, mediated by type 2 helper T cells and thyroid stimulating antibodies. Moreover, it is well established that ophthalmopathy may precede hyperthyroidism or occur after its resolution (particularly in smokers after treatment with radioactive iodine). GD can be found in association with other autoimmune disorders such as type 1 diabetes mellitus, Addison’s disease, vitiligo, pernicious anaemia, alopecia areata, myasthenia gravis, coeliac disease, systemic lupus erythematosus, Sjögren’s syndrome, and other HLA-DR3 associated diseases. The association with rheumatoid arthritis is rarer, but recognised, even in multiple autoimmune syndromes. So where there is autoimmunity with orbital involvement the absence of clinical hyperthyroidism should not rule out the diagnosis of GD.
Finally, the diagnosis of thyroid ophthalmopathy was unlikely because only one eye was affected. As suggested by the authors, magnetic resonance imaging is indicated to establish the correct diagnosis. This would show oedematous extraocular muscles with enlargement of the tendons in OM, and normal tendons in GD. Early response to systemic glucocorticoids confirms the diagnosis of OM.
Another disease that should be considered in the differential diagnosis is arteriovenous malformation, such as indirect carotid-cavernous fistula, which can develop spontaneously in older women. In this case the presence of a diffuse head murmur would be an important observation.2–5
We thank Dr Fadini for his interest in our case report of orbital myositis in association with rheumatoid arthritis.1
He rightly discusses in some detail the possibility of thyroid ophthalmopathy occurring in the absence of a systemic hyperthyroid diathesis. As we made clear in our article, there is a considerable variety of presenting clinical features in this condition. We sought to present these as concisely as possible, with particular reference to the most common presentation.
The differential diagnosis of an arteriovenous malformation was not likely in the clinical setting outlined. We agree that, ultimately, the diagnosis was made on the basis of typical magnetic resonance imaging findings and the prompt clinical response to corticosteroid treatment.
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