This is a rare case of a 57-year-old man who developed Sweet's syndrome (SS) secondary to Hashimoto thyroiditis (HT). He was initially misdiagnosed with cellulitis (a bacterial skin infection). HT is an autoimmune condition that causes an underactive thyroid.
Thyroid function tests should be part of the diagnostic examination of a patient with possible SS. These tests look at levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) in the blood. A high level of TSH and a low level of T4 can indicate an underactive thyroid. It may also be appropriate to test for thyroid peroxidase (TPO) antibodies even when there are no obvious signs or symptoms of thyroid dysfunction. Additional note: approx. 95% of patients with HT are positive for TPO antibodies.
The exact relationship between SS and HT is not understood. The two conditions may share a trigger or SS may stimulate the immune system in such a way that it leads to the development of HT.
POSSIBLE ROLE OF T-HELPER CELLS: T and B cells are immune cells/white blood cells called lymphocytes. T-helper cells are a type of T cell that provide help to other cells in the immune response by recognizing foreign invaders and secreting substances called cytokines. These cytokines then activate other T and B cells. There are different types of T-helper cell which can be placed into at least 2 main classes, Th1 and Th2.
Studies have suggested that Th1 cells play a greater role than Th2 cells in the development of SS. T-helper cells are also thought to be involved in the development of HT. A recent study showed that proportions of Th1 cells were significantly higher with overt hypothyroidism (increased TSH and low T4) compared to subclinical hypothyroidism (TSH slightly raised, but normal T4). This suggests that a greater amount of Th1 cells in SS may act as a trigger, 'pushing' a susceptible individual into clinical thyroid disease.
Goodwin, J., Ives, S. and Hashmi, H. (2020) Sweet Syndrome and Hashimoto Thyroiditis: A Case Report and Review of the Literature. American Association of Clinical Endocrinologists: Clinical Case Reports, Jul-Aug; 6(4): e179–e182 (PMC).