Case 3. Hashimoto’s thyroiditis :
Type IV Autoimmune disease
Pathologically Hashimoto’s thyroiditis represents an infiltration of thyroid gland with T and B lymphocytes, which often organize to form germinal centers. The lymphocytic infiltration may be visualized on positron emission tomography scanning. Patients with Hashimoto’s thyroiditis may exhibit a focal or diffusely increased 2 fluoro- 2 deoxy- D glucose (FGD) uptake, which correlates with the T/B-cell infiltration. The B cells make antibodies against thyroid antigens, as seen in this patient, whereas the T cells produce cytokines that stimulate the B cells and induce the thyroid cells to undergo apoptosis (programmed death). Eventually, the thyroid is destroyed and is unable to secrete thyroid hormone, resulting in hypothyroidism. The diffusely micronodular appearance on ultrasound is due to disruption of the normal microarchitecture of the thyroid gland. The small nodules seen on ultrasound (“pseudonodules”) represent germinal centers and areas of focal infiltration in the gland.