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Clinical Review

Diagnosis and management of thyrotoxicosis

BMJ 2006; 332 doi: https://doi.org/10.1136/bmj.332.7554.1369 (Published 08 June 2006) Cite this as: BMJ 2006;332:1369

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Diagnostic and Prognostic Utilty of Autoantibodies in Thyrotoxicosis

Graves’ disease is usually caused by production of autoantibodies
against Thyrotropin receptors (TSH-R Abs).
These TSH-R Abs mimic the effects of the thyroid stimulating hormone (TSH)
on thyroid cells leading to autonomous production of thyroxine and
triiodothyronine.
In her elegant review article on Diagnosis and Management of
Thyrotoxicosis, the Author Elizabeth N Pearce, has not been quite clear
about the diagnostic utility of different thyroid autoantibodies.
She mentions the presence of raised serum concentration of thyroperoxidase
antibodies (TPO) indicating an autoimmune thyroid disease and a raised
thyroid stimulating immunoglobulin (TSI) titre as indicative of Graves’
disease.

TSH-R Abs, the most specific antibodies for detection of Graves’
disease, were not mentioned in the review.
TSH-R Abs do not only confer a diagnostic value, but also a prognostic
one.
A high titre of these antibodies reflects the “immunologic” activity of
Graves’ disease. A declining titre is a good indicator of successful
treatment with antithyroid drugs or radioiodine treatment.
When on antithyroid drugs, a high titre of TSH-R Abs with a large goitre
are two important signs of poor chance of remission.
A high titre of TSH-R Abs might be associated with extrathyroidal
manifestations of Graves’ disease such as Graves’ ophthalmopathy and
dermopathy.
A high titre during pregnancy might be a risk factor for foetal
hyperthyroidism or even hypothyroidism (if the antibodies switch gear and
start to block the TSH receptors of the foetal thyroid in stead of
stimulating them).

TSI antibodies are a completely different set of antibodies. They do
stimulate thyroid growth; they are a risk factor for goitre in Graves’
disease. I use TSI very often in Graves’ disease associated with
pregnancy, but always in conjunction with TSH-R Abs. Their presence in
pregnant women might be a risk factor for foetal goitre. Sometimes goitres
big enough to obstruct labour.

TPO antibodies, although their titre might be high in Graves’
disease, are considered non specific for Graves’ disease, but they are
usually detected in all the 3 phases of Hashimoto’s thyroiditis, including
the thyrotoxic phase. We should bear in mind that not all patients with
Hashimoto’s thyroiditis go through an initial thyrotoxic phase.

Competing interests:
None declared

Competing interests: No competing interests

18 June 2006
Shirwan A. Mirza
Clinical Assistant Professor of Medicine
None
37 West Garden Street, Auburn, NY 13021, USA