When conditions of Graves' disease follow unusual phases, conditions of pre-existing or concurrent subacute thyroiditis (SAT) may be suspected. Subacute thyroiditis is a painful, inflammatory disease frequently accompanied by fever that causes a period of thyrotoxicosis lasting 2-3 months typically followed by a similar period of hypothyroidism. In patients with SAT who go on to develop Graves' disease, the onset of Graves' disease typically occurs within 1-8 months following SAT. In the interval between the end of SAT and the onset of Graves' disease there can be signs and symptoms of both diseases. 

In a study of 25,267 patients with thyroid disease followed between 1985 and 2008, researchers found 7 patients who followed this pattern. The age range of these patients was 40-66 years. The causes of Graves' disease following SAT remain unknown although the inflammatory nature of SAT may lead to the activation of the autoimmune response is susceptible patients.

In a previous blog, I mention that TSH receptor antibodies have been found in patients with SAT, usually at lower levels than those found in patients with Graves' disease suggesting that SAT may be an early phase of Graves' disease in some patients.  One way to distinguish SAT from Graves' disease is with an erythrocyte sedimentation rate (ESR, sed rate) blood test, which is normal in Graves' disease and elevated in patients with SAT.  Patients with Graves' disease have also been found to have concurrent conditions of SAT.

Resources:

Nakano Y, Kurihara H and J Sasaki. "Graves' disease following subacute thyroiditis." Tohoku Journal of Experimental Medicine. 2011;225(4):301-9.

 Sairaala, Eira. "Concurrent subacute thyroiditis and Graves' disease." Duodecim; 2012; 128(17): 1808-10.