Figure 420

Pituitary Cushing's disease. Pituitary Cushing's disease results from excessive production of adrenocorticotropic hormone (ACTH), typically owing to a benign adenoma. Excess ACTH stimulates both adrenals to produce excessive amounts of cortisol and results in bilateral adrenal hyperplasia. The increased cortisol production does not suppress ACTH release, however, because the pituitary tumor is unresponsive to the normal feedback suppression of increased cortisol levels. The diagnosis usually is made by demonstration of elevated levels of ACTH in the face of elevated cortisol levels, particularly in the afternoon or evening, representing loss of the normal circadian rhythm (see Fig. 4-4). Radiographic studies of the pituitary (computed tomographic scan and magnetic resonance imaging) will likely demonstrate the source of increased ACTH production. When the pituitary is the source, surgery and irradiation are therapeutic options.

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