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A 28-year-old woman is evaluated for fatigue, weight gain and occasional constipation. The patient has a history of craniopharyngioma, which was resected; she was subsequently given radiation therapy. She has hypopituitarism and diabetes insipidus after tumor resection and radiation. Her medications include hydrocortisone, levothyroxine, oral contraceptives, and desmopressin. She does not have dizziness, nausea, vomiting, polyuria, or polydipsia. She has regular menstrual cycles. The physical examination is unremarkable.
Laboratory Studies
Complete blood count
Normal
Electrolyte panel
Normal
TSH
0.1 µU/mL (0.1 mU/L)
Free T4
0.5 ng/dL (6.4 pmol/L)
Which of the following changes should be made to the patient therapy?
A Hydrocortisone dose should be lowered
B Oral contraceptives should be discontinued
C Desmopressin should be discontinued
D Thyroid hormone dose should be increased
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Correct Answer = D)
* The serum TSH cannot be used to monitor thyroid hormone replacement therapy in patients with central hypothyroidism
* On patients with central hypothyroidism, the goal of thyroid hormone replacement is to titrate the dose to normalize the free T4 (or total T4 and free thyroxine index) not to normalize the TSH.
This patient's thyroid hormone dose should be increased to normalize the free T4 level and alleviate signs and symptoms of hypothyroidism. The TSH cannot be used to monitor thyroid hormone replacement therapy in patients with central hypothyroidism. In these patients the pituitary thyrotropes do not produce adequate TSH to stimulate thyroid hormone production by the thyroid gland. It is not uncommon for such patients to have their thyroid hormone dose decreased because the suppressed TSH appears to suggest hormone over-replacement. The goal of thyroid hormone replacement in these patients is to titrate the dose to normalize the free T4 (or total T4 and free thyroxine index), not to normalize the TSH.
The hydrocortisone dose does not need to be reduced in the patient because she does not have any signs to suggest over-replacement. Similarly, the desmopressin dose should not be altered because her symptoms are controlled on her current dose and she has normal electrolytes. The desmopressin should not be discontinued as this patient who has had both surgery and radiation will undoubtedly have permanent diabetes insipidus. Finally, the patient is doing well on oral contraceptives and there is no reason to discontinue them. They will help prevent the development of osteopenia/osteoporosis induced by hypogonadism.
