Nevertheless, our observation regarding the Great Lakes probably pertains only to certain areas around the Great Lakes, but not to the entire region. Several studies are of interest in this regard. One study from Toronto found that silent thyroiditis occurs in 11% to 12% of hyperthyroid patients.4 Another study5 compared the prevalence of hyperthyroidism due to thyroiditis in Toronto with that of Cardiff, Wales. They found that subacute and silent thyroiditis occurred in 17% of hyperthyroid patients in Ontario and in only 1% in Wales (one case of subacute thyroiditis).5 These studies from Toronto, on the northern shore of Lake Ontario, compared with the data from Rochester, on the southern shore of Lake Ontario, suggest that even around the Great Lakes there is considerable variation in prevalence of silent thyroiditis.
It is also interesting that in the second study from Toronto, only 6% of patients had silent
Goldman JM. Thyrotoxic Silent Thyroiditis: A Geographic Puzzle-Reply. Arch Intern Med. 1985;145(12):2263-2264. doi:10.1001/archinte.1985.00360120135030