Cushing Syndrome and Pituitary Disease
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Answer: aThe findings of Cushing Syndrome often include central obesity, hypertension, hirsutism, fatigue, easy bruisability, stria, moon-like facies, dorsal fat pad, and often depression or other mental changes. Less common abnormalities include headache, osteoporosis, diabetes mellitus, galactorrhea, peripheral edema and amenorrhea. Often, a patient presents without the classic cushingoid appearance and complains only of severe fatigue or depression.
The cause of hypercortisolism is an ACTH-secreting pituitary adenoma (Cushing disease) in up to 80% of cases, with remainder due either to an adrenocortical tumor or to an ectopic neoplasm secreting ACTH or corticotropin-releasing factor. Pituitary-dependent hypercortisolism is much more common in women(80%) and an ectopic etiology more common in men.
Up to 60% of patients with pituitary etiologies have nondiagnostic imaging studies, therefore, the diagnosis often relies completely on endocrine testing. Multiple measurements of cortisol and ACTH to evaluate the diurnal pattern are important but often misleading.
They are mainly of value when clearly elevated. The determination of urinary free cortisol excretion over 24 hours is an extremely important measurement. If the overnight dexamethasone screening test yields an 8 AM serum cortisol level of less than 5 ug/dl, then hypercortisolism is rarely present.
Generally, patients with a pituitary etiology of hypercortisolism do not show suppression with the low-dose dexamethasone test, but do with the higher dose test. Patients with adrenal or ectopic etiologies do not experience suppression with either dose. Chest and abdominal CT scans are appropriate to look for adrenal or lung tumors.
The most specific test when the MRI is negative and evidence implicates the pituitary, is simultaneous measurement of ACTH levels in both inferior petrosal sinuses and a concurrent determination of the peripheral ACTH level. This approach produces specific information about the existence of an ACTH-secreting pituitary tumor and even the laterality of the tumor.
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