The reported incidence in MEN type I syndrome Patients may also be screened for gonadotropin-
varies from 0 to 100%.716'40 However, pituitary secreting tumor with basal- and thyrotropin-
abnormalities may be the first manifestation of releasing hormone-stimulated LH, LH-P, LH-a,
MEN type I; therefore, screening with prolactin lev- and FSH. Baseline free thyroxine (T4) and TSH will els is recommended. There is a 2 to 1 female-to- identify patients with central hypopituitarism and male ratio. When compared with sporadic pituitary the rare patient with a TSH-secreting tumor (an tumors, the overall distribution of tumor types is increase in T4 and increased level of TSH).16 altered in MEN type I; there are fewer gonadotropin Galactorrhea, amenorrhea, and/or infertility are and null cell tumors and more plurihormonal and common presentations in women with prolactinoma.
prolactin-producing tumors.41 The most common In men, hypogonadism and mass effect may be the pituitary adenoma associated with MEN type I is a only signs of prolactinoma. Prolactin levels are typ-
prolactinoma. Other hormones commonly secreted ically > 300 ng/mL.
by pituitary tumors associated with MEN type I The diagnosis of Cushing's syndrome is made by include GH, GH-prolactin, and ACTH (Figure increased glucocorticoid levels (increased 24-hour 16-5). Rarer tumors associated with MEN type I urine cortisol excretion) or diminished response of include luteinizing hormone (LH)/follicle-stimulat- glucocorticoid feedback. The feedback is most coming hormone (FSH), thyroid-stimulating hormone monly assessed by the overnight dexamethasone (TSH), and nonsecreting adenomas. Patients present suppression test (dexamethasone 1 mg orally at with symptoms and signs secondary to mass effect 11:00 pm should normally suppress cortisol to (headache, visual field loss), hypopituitarism, < 5 p,g/dL at 8:00 am). The differential diagnosis and/or excessive hormone production. includes pituitary-dependent ACTH excess (ade-The evaluation for pituitary tumors includes a noma or hyperplasia), ectopic ACTH from bronchial history of reproductive function (menstrual dates, carcinoid tumor, or primary neoplasm of the adrenal
Figure 16-5. Photographs of a typical patient with multiple endocrine neoplasia type I and acromegaly owing to a growth hormone-secreting pituitary adenoma. Note the prominent brow and mandible. He also had gradual enlargement of his hands and feet.
gland. The differential diagnosis begins with checking ACTH. Values < 10 pg/mL identify ACTH-inde-pendent Cushing's syndrome, in which case, a CT scan is indicated to evaluate the adrenal glands. If there is more than one lesion, then iodocholesterol scanning may be useful to identify functioning masses. Finally, the response to high-dose dexametha-sone can differentiate the ACTH-dependent forms of Cushing's syndrome, either ectopic or pituitary.42-44
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