How is pheochromocytoma best diagnosed?

For screening purposes, a 24-hour urine collection for vanillylmandelic acid (VMA), total catecholamines (epinephrine, norepinephrine), and metanephrine, normetanephrine, and creatinine will frequently establish the diagnosis in the hypertensive patient. Occasionally, urinary catecholamines and their metabolities collected during a typical spell will be helpful in diagnosing the patient with episodic disease. In patients requiring further evaluation, plasma catecholamines can be measured under standardized conditions; patients with pheochromocytoma have plasma catecholamine values 950 pg/ml (5.62 nmol/L). These values will not suppress on the clonidine suppression test. Provocative stimulation tests for pheochromocytoma such as glucagon, histamine, and tyramine are considered dangerous and should be avoided.

What is syndrome X?

This multimetabolic syndrome describes the association of certain clinical features and risk factors predictive of coronary artery disease: abdominal obesity (waist/hip 0.85), hypertension, carbohydrate intolerance or type II diabetes mellitus, and dyslipidemia (hypertriglyceridemia and low high-density lipoprotein [HDL] levels). The unifying associations with these clinical states are hyperinsulinemia and insulin resistance. Other related findings in these patients include hyperuricemia, physical inactivity, and aging. In contrast to this metabolic syndrome X, a cardiac syndrome X exists in which patients have anginal symptoms, normal coronary arteries on catheterization studies, but small, more distal occlusive disease (microvascular angina). Both syndromes may coexist in the same patient.

How common is coronary artery disease in patients with diabetes mellitus?

Coronary artery disease is the most common cause of morbidity and mortality in diabetic individuals, being 1.2-6.6 times more prevalent than in the nondiabetic population. Its predominance is even greater in individuals with non-insulin-dependent diabetes and in diabetic females. Seventy-seven percent of all diabetic hospitalizations are related to coronary artery disease.

What are the risk factors for coronary artery disease in diabetic patients?

Diabetes alone is an independent cardiovascular risk factor, along with the classic cardiac risk factors of advancing age, male gender, postmenopausal status in females, cigarette smoking, hypertension, family history of coronary artery disease, and dyslipidemia. Diabetes has been noted to amplify the effects of these classic risk factors for coronary artery disease. In patients with insulin-dependent diabetes mellitus, hypertension and proteinuria are the strongest risk factors associated with coronary artery disease. In individuals with non-insulin-dependent diabetes, hypertriglyceridemia and proteinuria are the most potent risk factors.

How is proteinuria implicated?

Proteinuria is the strongest predictor of cardiovascular mortality in all individuals with diabetes mellitus. It is frequently associated with hypertension and is a marker of renal disease. It is also associated with increased fibrinogen and increased platelet aggregability, as well as abnormalities in lipid profiles.

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