Medicine – Causes of Secondary Hyperlipidaemia

Secondary hyperlipidaemia means elevated blood lipids caused by an underlying disease, medication, lifestyle factor, or physiological state rather than by a primary inherited lipid disorder.

The pattern may be predominantly:

Raised cholesterol, especially LDL cholesterol,

or

Raised triglycerides,

although mixed abnormalities are common.

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1. Mainly Raised Cholesterol

Conditions that predominantly increase cholesterol include:

Hypothyroidism.

Cholestasis.

Nephrotic syndrome.

Renal transplantation.

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2. Hypothyroidism

Hypothyroidism commonly causes:

Raised total cholesterol

and

Raised LDL cholesterol.

The major mechanism is reduced hepatic expression and activity of:

LDL receptors.

This decreases clearance of LDL particles from the circulation.

Therefore:

HYPOTHYROIDISM → ↓ LDL CLEARANCE → ↑ LDL CHOLESTEROL.

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3. Lipid Pattern in Hypothyroidism

The typical pattern is:

↑ LDL cholesterol.

↑ Total cholesterol.

Triglycerides may also rise, especially in more severe disease, so the abnormality is not always purely hypercholesterolaemic.

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4. Clinical Importance

When otherwise unexplained hypercholesterolaemia is found, particularly with symptoms such as:

Fatigue.

Weight gain.

Cold intolerance.

Constipation.

it is reasonable to consider:

Hypothyroidism.

Treating the thyroid disorder may improve the lipid profile.

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5. Cholestasis

Cholestasis means impaired formation or flow of bile.

It can produce marked:

Hypercholesterolaemia.

This may occur in:

Extrahepatic biliary obstruction

or

Intrahepatic cholestatic disease.

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6. Mechanism in Cholestasis

An important abnormal lipoprotein can appear in cholestasis:

Lipoprotein X – Lp-X.

This cholesterol-rich particle contributes to the marked increase in measured serum cholesterol.

Therefore:

CHOLESTASIS → Lp-X ACCUMULATION → MARKED HYPERCHOLESTEROLAEMIA.

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7. Clinical Clues to Cholestasis

Associated features may include:

Jaundice.

Pruritus.

Dark urine.

Pale stools.

Raised alkaline phosphatase.

Thus a high cholesterol concentration in a jaundiced patient may reflect:

Cholestasis rather than a primary lipid disorder.

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8. Nephrotic Syndrome

The original notes correctly include:

Nephrotic syndrome.

The classic nephrotic picture consists of:

Heavy proteinuria.

Hypoalbuminaemia.

Oedema.

Hyperlipidaemia.

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9. Mechanism of Hyperlipidaemia in Nephrotic Syndrome

Loss of albumin in urine lowers plasma oncotic pressure and stimulates increased hepatic synthesis of proteins and lipoproteins.

At the same time, lipid clearance may also be impaired.

This produces increases in:

LDL.

VLDL.

Total cholesterol.

Triglycerides.

Therefore nephrotic syndrome may produce:

Mixed hyperlipidaemia, not only isolated hypercholesterolaemia.

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10. Typical Lipid Pattern in Nephrotic Syndrome

The most striking finding is often:

Markedly raised cholesterol.

However, triglycerides can also rise.

Therefore:

NEPHROTIC SYNDROME → ↑ CHOLESTEROL ± ↑ TRIGLYCERIDES.

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11. Renal Transplantation

Hyperlipidaemia is common after:

Renal transplantation.

The lipid pattern may include:

Raised total cholesterol.

Raised LDL.

Raised triglycerides.

So, again, it may be:

Mixed rather than purely cholesterol-predominant.

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12. Why Renal Transplantation Causes Dyslipidaemia

Several factors contribute, including:

Immunosuppressive medications.

Persistent CKD.

Weight gain.

Diabetes.

Hypertension.

Reduced physical activity.

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13. Immunosuppressive Drugs

Important transplant medications that can worsen lipid profiles include:

Corticosteroids.

Ciclosporin.

Sirolimus and related mTOR inhibitors.

Tacrolimus tends to have a less pronounced lipid effect than ciclosporin, although metabolic complications can still occur.

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14. Mainly Raised Triglycerides

Conditions that predominantly increase triglycerides include:

Obesity.

Insulin resistance.

Diabetes mellitus.

Chronic alcohol excess.

Several other secondary causes can also produce hypertriglyceridaemia.

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15. Obesity

Obesity, particularly:

Visceral or central obesity,

is strongly associated with:

Insulin resistance.

Insulin resistance increases release of free fatty acids from adipose tissue and promotes hepatic synthesis of:

Triglycerides and VLDL.

Therefore:

OBESITY → INSULIN RESISTANCE → ↑ VLDL → ↑ TRIGLYCERIDES.

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16. Insulin Resistance

Insulin normally suppresses:

Lipolysis in adipose tissue.

With insulin resistance, this suppression becomes less effective.

More free fatty acids reach the:

Liver.

The liver uses these fatty acids to synthesise:

Triglycerides.

These are exported mainly in:

VLDL particles.

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17. Metabolic Syndrome Pattern

The typical dyslipidaemia of insulin resistance includes:

Raised triglycerides.

Low HDL cholesterol.

Small dense LDL particles.

This pattern is often seen in:

Metabolic syndrome.

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18. Diabetes Mellitus

Poorly controlled diabetes, especially with marked insulin deficiency or resistance, can cause:

Hypertriglyceridaemia.

The mechanism includes:

Increased lipolysis.

Increased hepatic VLDL production.

Reduced triglyceride-rich lipoprotein clearance.

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19. Severe Hypertriglyceridaemia in Diabetes

Very poorly controlled diabetes can occasionally produce:

Severe hypertriglyceridaemia.

When triglycerides become extremely high, there is an increased risk of:

Acute pancreatitis.

Therefore severe triglyceride elevation should prompt assessment for:

Uncontrolled diabetes.

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20. Chronic Alcohol Excess

The original notes correctly include:

Chronic alcohol excess.

Alcohol increases hepatic:

Fatty acid synthesis

and

Triglyceride production.

It can therefore increase:

VLDL secretion.

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21. Alcohol and Triglycerides

The typical pattern is:

Raised triglycerides.

The rise may be particularly marked when alcohol excess occurs together with:

Obesity.

Diabetes.

High carbohydrate intake.

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22. Pancreatitis Risk

Alcohol excess can therefore contribute to pancreatitis in two different ways:

Direct alcohol toxicity

and

Severe hypertriglyceridaemia.

This becomes particularly relevant when triglycerides are very high.

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23. Other Important Causes of Secondary Hypertriglyceridaemia

Important additional causes include:

Pregnancy.

Chronic kidney disease.

Certain medications.

Excessive refined carbohydrate intake.

Some endocrine disorders.

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24. Pregnancy

During pregnancy, especially later pregnancy, triglycerides physiologically increase because of changes in:

Oestrogen.

Insulin resistance.

Hepatic lipoprotein production.

Usually this is physiological, but in susceptible individuals triglycerides can become markedly elevated.

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25. Chronic Kidney Disease

CKD commonly causes abnormalities in triglyceride-rich lipoprotein metabolism.

The typical pattern may include:

Raised triglycerides.

Reduced HDL.

LDL concentration may be normal or variably elevated.

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26. Medications Causing Hypertriglyceridaemia

Drugs that may increase triglycerides include:

Corticosteroids.

Oestrogens.

Retinoids.

Some antipsychotics.

Certain HIV therapies.

Some beta-blockers.

Thiazide diuretics, particularly at higher doses.

The degree of effect varies considerably between patients and agents.

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27. Mixed Secondary Hyperlipidaemia

Many secondary causes do not fit neatly into a single “cholesterol” or “triglyceride” category.

Examples include:

Nephrotic syndrome.

Renal transplantation.

Diabetes.

CKD.

These can produce:

Mixed dyslipidaemia.

Therefore the original classification is useful for memorisation but should not be considered absolute.

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28. Mainly Raised Cholesterol – Note Form

Hypothyroidism:

↓ LDL receptor activity.

↓

↓ LDL clearance.

↓

↑ LDL cholesterol.

⸻

Cholestasis:

Lipoprotein X accumulation.

↓

Marked hypercholesterolaemia.

⸻

Nephrotic syndrome:

↑ Hepatic lipoprotein synthesis + impaired clearance.

↓

↑ Cholesterol ± ↑ triglycerides.

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Renal transplantation:

Immunosuppressive drugs + metabolic factors.

↓

Often mixed dyslipidaemia.

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29. Mainly Raised Triglycerides – Note Form

Obesity:

Insulin resistance.

↓

↑ Free fatty acids.

↓

↑ Hepatic VLDL.

↓

↑ Triglycerides.

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Diabetes mellitus:

Insulin resistance or deficiency.

↓

↑ VLDL production + impaired clearance.

↓

↑ Triglycerides.

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Chronic alcohol excess:

↑ Hepatic triglyceride synthesis.

↓

↑ VLDL.

↓

↑ Triglycerides.

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30. Important Corrections and Clarifications

The original division into:

“mainly raised cholesterol”

and

“mainly raised triglycerides”

is useful for revision, but many secondary causes produce overlapping abnormalities.

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Nephrotic syndrome often produces:

BOTH HIGH CHOLESTEROL AND HIGH TRIGLYCERIDES, although cholesterol may be especially prominent.

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Renal transplantation can also produce:

MIXED DYSLIPIDAEMIA, rather than isolated hypercholesterolaemia.

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Diabetes particularly raises triglycerides when metabolic control is poor, and it often produces the characteristic insulin-resistant pattern of:

↑ TG + ↓ HDL + SMALL DENSE LDL.

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Key Clinical Pattern

For rapid recall:

HYPOTHYROIDISM → ↑ LDL CHOLESTEROL.

CHOLESTASIS → ↑ CHOLESTEROL, OFTEN VIA LIPOPROTEIN X.

NEPHROTIC SYNDROME → ↑ CHOLESTEROL ± ↑ TRIGLYCERIDES.

RENAL TRANSPLANT → MIXED DYSLIPIDAEMIA, OFTEN DRUG-RELATED.

OBESITY / INSULIN RESISTANCE / DIABETES → ↑ TRIGLYCERIDES.

ALCOHOL EXCESS → ↑ TRIGLYCERIDES.

A useful final distinction is:

CHOLESTEROL-PREDOMINANT → THINK HYPOTHYROIDISM, CHOLESTASIS, NEPHROTIC SYNDROME.

TRIGLYCERIDE-PREDOMINANT → THINK INSULIN RESISTANCE, DIABETES, OBESITY, ALCOHOL.