Figure 5a. Late-stage Hashimoto thyroiditis in a 59-year-old woman who complained of weight gain, diffuse muscle weakness, and somnolence. At physical examination, the patient’s thyroid felt very firm. Laboratory values were as follows: T4 = 2.8 µg/dL and TSH = 98 µIU/mL. The 24-hour RAIU was 7%. (a) Distant (left) and close-up (right) anterior images reveal nonuniform and relatively low thyroid activity compared with background activity. (b) Photomicrograph (original magnification, x200; H-E stain) of a histologic specimen obtained at open biopsy shows the thyroid architecture distorted by fibrosis with lymphoid follicles containing reactive germinal centers (arrow).