The patient, a 23-year-old woman, has had a bout of flulike symptoms over the past few weeks. Most recently,
she has become increasingly tired. She is taking birth control pills to control her menses. Her anterior neck
became painful during the past few weeks. The physical examination results reveal that her thyroid is diffusely
enlarged and mildly tender.
Studies
Results
Routine laboratory tests
Within normal limits (WNL)
Total thyroxine (T4), p. 497
8 meg/dL (normal: 5-12 meg /dL)
Free T4
0.5 ng/dL (normal: 0.8-2.7 ng/dL)
Free T4 index
0.4 ng/dL (normal: 0.8-2.4 ng/dL)
Triiodothyronine (T3), p. 506
52 ng/dL (normal: 70-205 ng/dL)
Thyroxine-binding globulin (TBG), p. 495
12 mg/dL (normal: 1.7-3.6 mg/dL)
Thyroid stimulating hormone (TSH), p. 486
32 microunits/mL (normal: 2-10 microunits/mL)
Thyroid scanning, p. 839
Enlarged gland; normal shape, position, and function of the thyroid gland. No areas of decreased or increased
uptake
Thyroid ultrasound, p. 895
Enlarged gland; normal shape and position of the thyroid gland
Thyroid antibodies
Antithyroglobulin antibody, p. 102
1:250 (normal: titer <1:100)
Antithyroid peroxidase antibody, p. 104
1:500 (normal: titer <1:100)
Thyroid-stimulating immunoglobulins, p. 494
Negative
Diagnostic Analysis
Total T4 measures protein-bound and unbound T4. Because the patient was taking birth control pills, her TBG
was elevated; therefore, her total T4 was normal. Free T4 and FT4 index tests measure unbound T4. When the
free T4 and the FT4 index were measured, they were found to be low, indicating that the patient had
hypothyroidism. The TSH level was elevated because of primary failure of the thyroid. The thyroid antibodies
were elevated, indicating that the patient had Hashimoto thyroiditis. Her long-acting thyroid stimulator (LATS)
levels were normal, discounting Graves disease as a cause of her diffusely enlarged thyroid. Her thyroid
ultrasound and scan failed to show any localized, defined tumor.
The patient was started on thyroid replacement therapy, and her TSH level returned to normal. Over the next
few weeks, she felt markedly better. Her thyroid pain and tiredness disappeared.
Critical Thinking Questions
- Why were the thyroid antibodies important in this patient’s diagnosis?
- What symptoms might she experience if too much thyroid replacement medication were administered?
Sample Solution
