Medicine – Hyperlipidaemias

Hyperlipidaemia refers to an abnormal increase in circulating lipids or lipoproteins, particularly LDL cholesterol and triglyceride-rich particles. These abnormalities are clinically important because prolonged exposure to atherogenic lipoproteins contributes to the development of atherosclerotic cardiovascular disease – ASCVD.

Hyperlipidaemia may be primary, due to inherited disorders of lipid metabolism, or secondary, due to conditions such as hypothyroidism, diabetes, nephrotic syndrome, cholestasis, obesity, alcohol excess or certain medications.

1. Lipids and Atherosclerotic Disease

The original notes state that atherosclerotic disease is associated with:

High total cholesterol.

High LDL cholesterol.

High triglycerides.

This is broadly correct, although the strength and mechanism of association differ between these measurements.

2. LDL Cholesterol

Low-density lipoprotein – LDL is the major cholesterol-carrying atherogenic lipoprotein in the circulation.

Persistently elevated LDL promotes cholesterol deposition within the:

Arterial wall.

This contributes directly to:

Atherosclerotic plaque formation.

Therefore:

HIGH LDL → HIGHER ASCVD RISK.

3. LDL and the Arterial Wall

LDL particles cross the vascular endothelium and become retained within the arterial intima.

They can then undergo modification, including:

Oxidation.

Modified LDL promotes recruitment of:

Monocytes and macrophages.

Macrophages ingest the lipid and become:

Foam cells.

4. Formation of Atherosclerotic Plaque

Accumulation of foam cells initially produces:

Fatty streaks.

With continuing lipid deposition and inflammation, this may progress to:

Fibrous atherosclerotic plaques.

These plaques may gradually narrow the arterial lumen or rupture and provoke:

Acute thrombosis.

5. Clinical Consequences of Atherosclerosis

Depending on the affected circulation, atherosclerotic disease may cause:

Coronary artery disease.

Myocardial infarction.

Ischaemic stroke.

Transient ischaemic attack.

Peripheral arterial disease.

Therefore LDL lowering is one of the major strategies for prevention of cardiovascular disease.

6. Total Cholesterol

Total cholesterol includes cholesterol carried in several lipoprotein classes, particularly:

LDL.

HDL.

VLDL and remnant particles.

Therefore total cholesterol alone does not tell us exactly how much cholesterol is present in:

Atherogenic particles.

7. Why Total Cholesterol Can Be Misleading

A high total cholesterol may occur because LDL is elevated, which increases cardiovascular risk.

However, total cholesterol can also be influenced by:

HDL cholesterol.

Therefore modern cardiovascular risk assessment generally places greater emphasis on:

LDL cholesterol

and measures of total atherogenic lipoprotein burden.

8. Non-HDL Cholesterol

An important useful measurement is:

Non-HDL cholesterol.

This represents:

Total cholesterol minus HDL cholesterol.

It therefore includes cholesterol contained within essentially all major:

ApoB-containing atherogenic particles.

These include:

LDL.

VLDL.

IDL.

Remnant lipoproteins.

Lipoprotein(a).

9. ApoB

Apolipoprotein B – ApoB is present as one major structural ApoB molecule on each atherogenic lipoprotein particle.

Therefore ApoB can provide an estimate of the:

Number of circulating atherogenic particles.

This may be especially useful when LDL cholesterol and particle number are discordant, such as in:

Diabetes.

Metabolic syndrome.

Hypertriglyceridaemia.

10. Triglycerides

Raised triglycerides are also associated with increased cardiovascular risk.

However, the triglyceride molecule itself is not generally considered the primary substance directly deposited in the arterial wall in the same way as cholesterol carried in LDL.

Instead, elevated triglycerides often indicate increased numbers of:

Triglyceride-rich lipoproteins and their remnants.

11. Triglyceride-Rich Remnant Particles

These particles include remnants derived from:

VLDL

and

Chylomicrons.

Remnant particles carry substantial cholesterol and can enter the arterial wall.

They are therefore considered:

Atherogenic.

Thus:

HIGH TRIGLYCERIDES OFTEN SIGNAL INCREASED ATHEROGENIC REMNANT PARTICLES.

12. Causes of Raised Triglycerides

Common causes include:

Obesity.

Insulin resistance.

Diabetes mellitus.

Alcohol excess.

Chronic kidney disease.

Some medications.

Inherited hypertriglyceridaemia.

13. Severe Hypertriglyceridaemia

When triglycerides become very high, the immediate clinical concern shifts toward:

Acute pancreatitis.

Therefore triglycerides have two major clinical implications:

Moderate elevation → increased cardiovascular risk.

Severe elevation → pancreatitis risk.

14. HDL Cholesterol

High-density lipoprotein – HDL participates in cholesterol transport and has historically been considered:

Protective against atherosclerosis.

Epidemiological studies consistently show that low HDL cholesterol is associated with:

Higher cardiovascular risk.

15. Reverse Cholesterol Transport

One important function of HDL is:

Reverse cholesterol transport.

HDL accepts cholesterol from peripheral tissues, including cells within the arterial wall, and transports it toward the:

Liver.

The cholesterol can then be recycled or eliminated through:

Biliary pathways.

This helps explain the traditional description of HDL as:

“Good cholesterol.”

16. HDL Has Other Biological Functions

HDL particles also have properties related to:

Cholesterol efflux.

Antioxidant activity.

Endothelial function.

Inflammatory regulation.

However, HDL biology is complex and cannot be reduced simply to the amount of cholesterol measured inside HDL particles.

17. Important Correction – Is High HDL Always Protective?

The original statement:

“HDL protective”

is useful for basic teaching but is somewhat oversimplified.

A higher HDL cholesterol level is generally associated observationally with lower cardiovascular risk, but:

Artificially increasing HDL cholesterol has not consistently been shown to reduce cardiovascular events.

Therefore modern treatment does not primarily aim to raise HDL levels.

Instead, the strongest therapeutic emphasis is on lowering:

LDL and other ApoB-containing atherogenic lipoproteins.

18. Low HDL

Low HDL is commonly associated with:

Obesity.

Insulin resistance.

Type 2 diabetes.

Smoking.

Physical inactivity.

Hypertriglyceridaemia.

It often occurs as part of the dyslipidaemia of:

Metabolic syndrome.

19. Typical Insulin-Resistance Lipid Pattern

Insulin resistance often produces:

Raised triglycerides.

Low HDL.

Small dense LDL particles.

This combination is particularly associated with increased:

Atherosclerotic cardiovascular risk.

20. Primary Hyperlipidaemia

Primary disorders arise largely from:

Inherited abnormalities of lipoprotein metabolism.

Important examples include:

Familial hypercholesterolaemia.

Familial combined hyperlipidaemia.

Familial hypertriglyceridaemia.

Familial chylomicronaemia syndromes.

21. Secondary Hyperlipidaemia

Secondary hyperlipidaemia develops because of another condition or exposure.

Important causes include:

Hypothyroidism.

Diabetes mellitus.

Obesity and insulin resistance.

Nephrotic syndrome.

Chronic kidney disease.

Cholestasis.

Alcohol excess.

Renal transplantation and some medications.

Therefore secondary causes should be considered before assuming every abnormal lipid result represents a purely inherited disorder.

22. Familial Hypercholesterolaemia

Familial hypercholesterolaemia produces:

Markedly elevated LDL cholesterol from a young age.

It is associated with:

Tendon xanthomas.

Premature coronary artery disease.

Early myocardial infarction if untreated.

This condition demonstrates particularly clearly the causal relationship between prolonged LDL exposure and atherosclerosis.

23. Lipid Deposits

Severe lipid disorders may cause visible lipid deposition.

Examples include:

Tendon xanthomas → especially familial hypercholesterolaemia.

Eruptive xanthomas → severe hypertriglyceridaemia.

Xanthelasma → may accompany hypercholesterolaemia but is less specific.

Corneal arcus in a young person → may suggest significant hypercholesterolaemia.

24. Assessment of Hyperlipidaemia

A lipid profile commonly includes:

Total cholesterol.

LDL cholesterol.

HDL cholesterol.

Triglycerides.

Depending on the clinical context, assessment may also include:

Non-HDL cholesterol.

ApoB.

Lipoprotein(a).

25. Lipoprotein(a)

Lipoprotein(a) – Lp(a) is an LDL-like particle containing:

ApoB

linked to:

Apolipoprotein(a).

Its level is largely genetically determined.

Elevated Lp(a) is an independent risk factor for:

Atherosclerotic cardiovascular disease

and

Calcific aortic valve disease.

26. Treatment Principles

The primary aim of treatment is to reduce:

Atherosclerotic cardiovascular risk.

Management includes:

Dietary improvement.

Regular physical activity.

Weight management where appropriate.

Smoking cessation.

Management of diabetes and hypertension.

Treatment of secondary causes.

27. LDL-Lowering Therapy

The major drug class used to lower LDL is:

Statins.

Statins inhibit:

HMG-CoA reductase.

This decreases hepatic cholesterol synthesis and increases hepatic:

LDL receptor expression.

The result is:

Reduced circulating LDL cholesterol.

28. Additional LDL-Lowering Therapy

When greater LDL reduction is needed, therapy may include:

Ezetimibe.

PCSK9-targeted therapies.

Other agents may be considered according to cardiovascular risk, lipid phenotype and clinical circumstances.

29. Triglyceride-Lowering Therapy

Management of high triglycerides includes addressing:

Obesity.

Poor glycaemic control.

Alcohol intake.

Dietary factors.

Secondary causes.

In selected patients, medications such as:

Fibrates

may be appropriate, particularly when triglycerides are markedly elevated.

30. Important Corrections to the Original Notes

The statement:

“Atherosclerotic disease associated with high total cholesterol, LDL and triglycerides”

is broadly correct, but the major directly causal treatment target is:

LDL AND OTHER ApoB-CONTAINING ATHEROGENIC LIPOPROTEINS.

Total cholesterol is useful but less informative by itself because it includes cholesterol carried in both:

Atherogenic LDL-type particles

and

HDL.

Raised triglycerides are associated with cardiovascular risk largely because they reflect increased:

TRIGLYCERIDE-RICH REMNANT LIPOPROTEINS, which contain atherogenic cholesterol.

The statement:

“HDL protective”

is best refined to:

LOW HDL IS ASSOCIATED WITH HIGHER CARDIOVASCULAR RISK, BUT SIMPLY RAISING HDL PHARMACOLOGICALLY DOES NOT NECESSARILY REDUCE THAT RISK.

The main therapeutic focus remains:

REDUCING LDL/ApoB-CONTAINING PARTICLES.

Key Clinical Pattern

Remember:

↑ LDL → STRONG CAUSAL DRIVER OF ATHEROSCLEROSIS.

↑ TOTAL CHOLESTEROL → MAY REFLECT ↑ ATHEROGENIC CHOLESTEROL, BUT INTERPRET COMPONENTS.

↑ TRIGLYCERIDES → REMNANT-PARTICLE/ASCVD RISK; VERY HIGH LEVELS → PANCREATITIS RISK.

↓ HDL → ASSOCIATED WITH INCREASED CARDIOVASCULAR RISK.

And the most important modern principle is:

ATHEROSCLEROTIC RISK IS DRIVEN PARTICULARLY BY CUMULATIVE EXPOSURE TO ApoB-CONTAINING LIPOPROTEINS, ESPECIALLY LDL.