Review Question - QID 214901

This patient who presents with weakness, hirsutism, central obesity, hypertension, and bruising most likely has Cushing syndrome secondary to a pituitary adenoma given the headaches and bitemporal hemianopsia. Overactivity of the adrenal glands in this syndrome will lead to increased conversion of norepinephrine to epinephrine.

The adrenal gland is divided into a cortex and a medulla. The cortex is further subdivided into the zona glomerulosa which produces aldosterone, the zona fasciculata which produces cortisol, and the zona reticularis which produces sex steroids such as dehydroepiandrosterone. The adrenal medulla serves as an end-organ target of the sympathetic nervous system and converts norepinephrine to epinephrine through the action of phenylethanolamine n-methyltransferase. Hypertrophy of the adrenal glands will cause increased production of both cortisol and epinephrine, which can result in the development of hypertension in the setting of Cushing syndrome. This form of hypertension is distinct from that found in hyperaldosteronism, which is regulated separately by the renin-angiotensin-aldosterone system originating from the juxtaglomerular apparatus of the kidney.

Incorrect Answers:
Answer 1: Acetylcholine to acetate conversion would be increased in patients with myasthenia gravis, which can cause proximal weakness that gets worse with prolonged muscle use. These patients would not have associated symptoms of central obesity, bruising, or hirsutism.

Answer 2: Hydroxycorticosterone to aldosterone conversion would be increased in Conn syndrome, which presents with isolated severe hypertension in otherwise healthy patients. Aldosterone is not classically elevated in patients with Cushing syndrome because the production of this hormone is regulated independently by the renin-angiotensin-aldosterone system.

Answer 3: Insulin to C-peptide conversion may be increased in the early stages of diabetes mellitus due to peripheral insulin resistance. Diabetes may be asymptomatic if mild or present with polydipsia and polyuria if severe.

Answer 5: Thyroglobulin to thyroxine conversion would be increased in Graves disease, which may also present with muscle weakness; however, these patients would have associated symptoms of hyperthermia, exophthalmos, and heat intolerance.

Bullet Summary:
Norepinephrine to epinephrine conversion by phenylethanolamine n-methyltransferase in the adrenal medulla will be increased in patients with Cushing syndrome.