MKSAP Quiz: three-month history of sweating, appetite and weight loss
MKSAP Quiz: three-month history of sweating, appetite and weight loss
A 38-year-old woman is evaluated for a 3-month history of increased sweating, increased appetite, and a 7.3-kg (16-lb) weight loss. The patient also reports a 4-month history of amenorrhea, before which time she felt "completely healthy." Medical history is otherwise unremarkable, and she takes no medications.
Physical examination shows a thin, restless woman with smooth, fine, moist skin and fine hair. Blood pressure is 108/60 mm Hg, pulse rate is 96/min, respiration rate is 14/min, and BMI is 18.1. Mild lid lag is noted, but no proptosis, diplopia, or conjunctival injection is detected. Her thyroid gland is soft and enlarged approximately twofold. There is a mild, fine tremor of the outstretched hands. Reflexes are brisk.
Laboratory studies:
| Thyroid-stimulating hormone | 2.4 µU/mL (2.4 mU/L) |
| Thyroxine (T4), free | 2.7 ng/dL (34.8 pmol/L) |
| Triiodothyronine (T3), total | 387 ng/dL (5.96 nmol/L) |
Which of the following is the most appropriate next test to perform on this patient?
A. MRI of the pituitary gland
B. Thyroid anti–peroxidase antibody test
C. Thyroid radioactive iodine uptake determination
D. Thyroid scan
E. Thyroid-stimulating immunoglobulin measurement
MKSAP Answer and Critique
The correct answer is A) MRI of the pituitary gland. This item is available to online to MKSAP 15 subscribers as item 41 in the Endocrinology and Metabolism module.
This patient should undergo MRI of the pituitary gland to detect a possible thyroid-stimulating hormone (TSH)–secreting tumor. This patient clinically has hyperthyroidism, and testing shows clearly elevated levels of free thyroxine (T4) and total triiodothyronine (T3). However, her serum TSH level is not suppressed, as it is in almost all causes of hyperthyroidism. This incongruity raises the possibility of a TSH-secreting pituitary adenoma as the cause of her hyperthyroidism.
Antiperoxidase antibodies are usually present in patients with autoimmune thyroid disease, such as Hashimoto disease. The presence or absence of such antibodies in this patient with a probable TSH-secreting pituitary adenoma, however, would not be diagnostically helpful.
A determination of thyroid radioactive iodine uptake helps to quantitate hyperactivity in the thyroid gland and may help differentiate thyroiditis from Graves disease. In this patient, the uptake would not be useful in the differential diagnosis because the patient most likely has a TSH-secreting pituitary adenoma and not a primary thyroid gland disorder.
A thyroid scan is useful in showing functional morphology of a gland. Although a thyroid scan is likely to show diffuse hyperfunction in this patient, it would not be useful in the differential diagnosis because the most likely cause of this patient's symptoms is not primary thyroid disease but a TSH-secreting pituitary adenoma.
Patients with Graves disease have an unregulated production of T4 and T3 because of the presence of autoantibodies, such as thyroid-stimulating immunoglobulin, against the TSH receptor, but these autoantibodies are not always present at all time points. In this patient, the titer of such antibodies is likely to be low because the cause of this patient's hyperthyroidism is not likely to be Graves disease.
Key Point
- In a patient with hyperthyroidism, the finding of an inappropriately normal level of thyroid-stimulating hormone suggests a pituitary cause of the hyperthyroidism.