Hyperlipidaemia

Hyperlipidaemia is a medical condition characterised by abnormally elevated levels of lipids or lipoproteins in the blood. This condition can involve any or all types of lipids, including fats, triglycerides, cholesterol, and phospholipids. The term encompasses various acquired or genetic disorders that result in elevated lipid levels.

Hyperlipidaemia is a subset of dyslipidaemia and a superset of hypercholesterolaemia, often requiring chronic management with ongoing medication to control blood lipid levels.

A 4-ml sample of hyperlipidaemic blood in a vacutainer with EDTA. Left to settle for four hours without centrifugation, the lipids separated into the top fraction.

Classification

Hyperlipidaemias are classified into primary (familial) and secondary (acquired) subtypes. Primary hyperlipidaemia results from genetic causes, such as mutations in receptor proteins, while secondary hyperlipidaemia arises from other underlying conditions like diabetes. Lipid and lipoprotein abnormalities are modifiable risk factors for cardiovascular disease and can predispose individuals to acute pancreatitis.

Familial (Primary) Hyperlipidaemias

Familial hyperlipidaemias are classified according to the Fredrickson classification, which is based on lipoprotein patterns observed through electrophoresis or ultracentrifugation. This classification includes several types:

Type I: Characterised by lipoprotein lipase deficiency or altered apolipoprotein C2, leading to elevated chylomicrons. Symptoms include acute pancreatitis, lipaemia retinalis, and hepatosplenomegaly. Treatment involves diet control.

Type IIa: Results from LDL receptor deficiency, presenting with xanthelasma, arcus senilis, and tendon xanthomas. Treatment includes bile acid sequestrants, statins, and niacin.

Type IIb: Involves decreased LDL receptor and increased ApoB, leading to elevated LDL and VLDL levels. Treatment includes statins, niacin, and fibrates.

Type III: Caused by defects in Apo E2 synthesis, leading to elevated IDL levels. Symptoms include tuberoeruptive xanthomas and palmar xanthomas. Treatment involves fibrates and statins.

Type IV: Characterised by increased VLDL production and decreased elimination, which can cause pancreatitis at high triglyceride levels. Treatment includes fibrates, niacin, and statins.

Type V: Similar to Type I but with elevated VLDL in addition to chylomicrons. Treatment includes niacin and fibrates.

Relative prevalence of familial forms of hyperlipoproteinaemia

Acquired (Secondary) Hyperlipidaemias

Acquired hyperlipidaemias often mimic primary forms and can result from conditions such as diabetes mellitus, hypothyroidism, kidney failure, and certain medications (e.g., thiazide diuretics, beta blockers, estrogens). Treatment of the underlying condition or discontinuation of the offending drugs usually improves hyperlipidaemia.

Signs and Symptoms

Hyperlipidaemia predisposes individuals to atherosclerosis, which is the accumulation of lipids, cholesterol, calcium, and fibrous plaques within artery walls. This can lead to narrowed blood vessels, reduced blood flow, and oxygen supply to the heart muscles, potentially causing angina or myocardial infarction. Atherosclerosis in arteries supplying the brain can lead to strokes.

Diagnosis

Screening for hyperlipidaemia involves measuring serum levels of LDL, HDL, and triglycerides. Adults over 20 should have their cholesterol checked every four to six years. Risk assessment tools like the Framingham Risk Score help stratify cardiovascular disease risk and guide medical intervention.

Lipid Levels

• Total Cholesterol: Combined LDL and HDL levels; over 240 mg/dL is abnormal.
• LDL Cholesterol: "Bad cholesterol"; elevated levels are associated with increased cardiovascular disease risk.
• HDL Cholesterol: "Good cholesterol"; higher levels are protective against cardiovascular disease.
• Triglycerides: Elevated triglycerides are an independent risk factor for cardiovascular disease.

Treatment

Management of hyperlipidaemia includes lifestyle modifications and medication.

Lifestyle Modifications

Maintaining a normal body weight, increasing physical activity, reducing refined carbohydrates and simple sugars, and quitting smoking are essential.

Medications

• Statins: Inhibit HMG-CoA reductase, reducing LDL cholesterol.
• Fibric Acid Derivatives: Increase lipolysis in adipose tissue, reducing VLDL and LDL levels.
• Niacin: Decreases LDL cholesterol and triglycerides, and increases HDL cholesterol.
• Bile Acid Binding Resins: Increase excretion of bile acids, reducing LDL cholesterol.
• Sterol Absorption Inhibitors: Decrease cholesterol absorption in the GI tract, reducing LDL cholesterol.

Prevention

Preventive measures include quitting smoking, reducing saturated fat and alcohol intake, losing excess body weight, and adopting a diet rich in fruits, vegetables, and whole grains.

Self-assessment MCQs (single best answer)

Which of the following best describes hyperlipidaemia?

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What is the primary subtype of hyperlipidaemia?

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Which type of familial hyperlipidaemia is characterised by lipoprotein lipase deficiency?

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What is the main cause of Type IIa familial hyperlipidaemia?

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Which of the following is NOT a common treatment for hyperlipidaemia?

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Which medication increases excretion of bile acids to reduce LDL cholesterol?

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What is the recommended frequency for cholesterol checks in adults over 20?

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Which lipid level is referred to as "bad cholesterol"?

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What is a common symptom associated with atherosclerosis due to hyperlipidaemia?

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Which lifestyle modification is recommended for managing hyperlipidaemia?

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