LIPID DISORDERS
GENERAL FEATURES
• More than 25% of the adult US population has hyperlipidemia. Despite wide promotion of the National Cholesterol Education Program Adult Treatment Panel (ATP) III guidelines, control of hyperlipidemia remains suboptimal.
• A strong familiar tendency toward hyperlidemia exists, and 70% of patients with lipid abnormalities have a family history of a lipid disorder.
• Lipoproteins are classified into five subclasses: chylomicrons, very-lowdensity lipoprotein, intermediatedensity lipoprotein, low-density lipoprotein (LDL), and high-density lipoprotein (HDL).
• LDL cholesterol (LDL-C) is the major carrier of cholesterol to peripheral tissues. The reverse transport lipoprotein, HDL cholesterol (HDLC), carries cholesterol back to the liver to be excreted as bile salts. HDL-C is referred to as the good cholesterol.
• Risk of atherosclerotic vascular disease increases with increasing levels of LDL-C in both sexes and for people from different racial and ethnic groups.
• LDL-C promotes atherosclerosis by damaging the endothelium, altering vascular tone, increasing platelet aggregation, activating pro-inflammatory signaling pathways, and inducing growth factors.
• Risk of coronary heart disease (CHD) increases with decreasing levels of HDL-C.
• Lowering LDL-C level in patients with CHD significantly reduces mor tality and recurrence of cardiovascular events.
• Several types of primary familial hypercholesterolemia are caused by genetic disorders of lipid metabolism. Patients with certain genetic lipid disorders should be referred to a lipid specialist.
• Secondary causes of hyperlipidemia include obesity, hypothyroidism, diabetes, chronic renal failure, nephrotic syndrome, obstructive liver disease, and certain medications.
CLINICAL ASSESSMENT
• History
– Ascertain family history of hyperlipidemia, premature MI, or sudden cardiac death; delineate other cardiovascular risk factors, such as smoking, alcohol intake, diet, physical activity, and diabetes.
— Patients with mild hyperlipidemia are usually asymptomatic.
— Symptoms of angina, transient ischemic attack, fatigue, and dyspnea suggest atherosclerotic vascular involvement.
— Patients with severe hypertriglyceridemia may complain of nausea, vomiting, and abdominal pain related to pancreatitis.
• Physical examination
— Few clinical findings are seen in patients with hyperlipidemia, and often physical examination findings are within normal limits.
— BP, waist circumference, weight, signs of vascular compromise, and presence of corneal opacification should be noted.
— Xanthomas are occasionally seen in patients with familial lipid disorders or extremely high cholesterol levels.