Dyslipidemia and Atherosclerosis

Primary (genetic) dyslipidemias — defects in lipoprotein handling

• Familial hypercholesterolemia: loss-of-function mutation in the LDL receptor (most common), defective apoB-100, or gain-of-function PCSK9 (PCSK9 degrades recycled LDL receptors) → impaired hepatic LDL clearance. Isolated LDL elevation, tendon xanthomas, premature ASCVD.
• Familial dysbetalipoproteinemia (type III): apoE2/E2 homozygosity impairs hepatic uptake of chylomicron and VLDL remnants → both cholesterol and triglycerides elevated; palmar crease xanthomas and tuberoeruptive xanthomas are the giveaway.
• Familial chylomicronemia (type I): lipoprotein lipase or apoC-II deficiency prevents chylomicron hydrolysis → milky serum, eruptive xanthomas, lipemia retinalis, pancreatitis; atherosclerosis is not the classic complication.
• Familial combined hyperlipidemia: hepatic apoB overproduction with mixed LDL/triglyceride elevation; the most common inherited dyslipidemia.

Secondary (acquired) causes — always excluded before labeling a lipid disorder primary

• Endocrine: hypothyroidism (downregulated LDL receptor expression), insulin resistance and type 2 diabetes (VLDL overproduction, reduced LPL activity, small dense LDL, low HDL).
• Renal/hepatic: nephrotic syndrome (low oncotic pressure drives hepatic lipoprotein synthesis), chronic kidney disease, cholestasis.
• Ingested/iatrogenic: alcohol and obesity (triglyceride-predominant); thiazides, non-selective beta blockers, glucocorticoids, oral estrogen, protease inhibitors, second-generation antipsychotics, cyclosporine, isotretinoin.

Non-modifiable risk factors

• Age and male sex: risk rises steeply with age; women catch up after menopause.
• Family history of premature ASCVD: first-degree male relative <55 or female <65 years.
• Genetic markers: elevated Lp(a) and South Asian ancestry are both listed as risk-enhancing factors in the 2018 ACC/AHA Cholesterol Guideline.

Modifiable risk factors examiners plant in the stem

• Smoking, hypertension, diabetes, obesity, sedentary lifestyle, atherogenic diet: the classic quartet plus lifestyle; smoking and diabetes carry the heaviest weight in the pooled cohort equations used by the 2019 ACC/AHA Primary Prevention Guideline.
• Risk-enhancing conditions: metabolic syndrome, CKD, chronic inflammatory disease (rheumatoid arthritis, psoriasis, HIV), preeclampsia or premature menopause, persistently elevated triglycerides, and elevated hs-CRP — these tip an intermediate-risk patient toward statin therapy.

• Lipoprotein metabolism and LDL oxidation: LDL particles penetrate the arterial intima, where they undergo oxidation (oxLDL) by resident macrophages and smooth muscle cells. Oxidized LDL is highly atherogenic, triggering recruitment of monocytes via chemotactic signals (MCP-1) and expression of adhesion molecules (ICAM-1, VCAM-1) on endothelial cells.

• Macrophage foam cell formation: Monocytes differentiate into macrophages that engulf oxLDL via scavenger receptors (SR-A, LOX-1), becoming engorged with lipid to form foam cells—the hallmark of early atherosclerotic lesions (fatty streaks).

• Arterial inflammation and plaque progression: Foam cells release pro-inflammatory cytokines (TNF-α, IL-1, IL-6) and proteases that attract smooth muscle cells from the media into the intima. These smooth muscle cells proliferate and produce extracellular matrix (collagen, elastin), forming a fibrous cap over the lipid-rich necrotic core. Reduced HDL and elevated triglycerides impair this process, promoting plaque instability.

• Endothelial dysfunction: High LDL and low HDL reduce nitric oxide (NO) bioavailability, impairing vasodilation and promoting vasoconstriction. Loss of NO's protective effects accelerates atherosclerosis through increased oxidative stress, platelet aggregation, and leukocyte adhesion.

• Thrombosis and acute events: Vulnerable plaques with thin fibrous caps, large lipid cores, and abundant inflammatory cells may rupture, exposing tissue factor and collagen. This triggers acute thrombosis with platelet aggregation and coagulation cascade activation, causing acute coronary syndrome (ACS) or stroke.

• Role of triglycerides and remnants: Elevated triglycerides promote atherosclerosis independently; triglyceride-rich lipoproteins (VLDL, chylomicron remnants) deliver cholesterol to arterial walls and promote oxidation and inflammation.

• Asymptomatic dyslipidemia: The majority of patients with dyslipidemia are asymptomatic and identified only through screening lipid panels. This silent nature makes routine screening critical in adults ≥20 years old and essential in those with ASCVD risk factors.

• Xanthomas and xanthelasmas: Tendon xanthomas (firm nodules on Achilles tendon or extensor tendons of hands) and eruptive xanthomas (yellow papules on buttocks/extensor surfaces) indicate severely elevated lipids, particularly in familial hypercholesterolemia (FH). Xanthelasmas (yellow deposits around eyelids) may indicate dyslipidemia but are nonspecific.

• Corneal arcus: A gray-white ring at the corneal periphery can occur in dyslipidemia, especially FH; notable when present in patients <40 years old and suggests aggressive lipid abnormality.

• Acute coronary syndrome (ACS): Patients may present with chest pain, dyspnea, diaphoresis, or cardiogenic shock from atherosclerotic plaque rupture and thrombosis. This represents the clinical manifestation of years of silent atherosclerosis accumulation.

• Stroke or transient ischemic attack (TIA): Atherosclerotic disease in carotid and cerebral arteries may present acutely with focal neurologic deficits, highlighting dyslipidemia's systemic vascular effects.

• Peripheral arterial disease (PAD): Claudication (calf pain with walking) or critical limb ischemia reflects atherosclerotic disease in lower extremity vessels; often accompanies coronary and cerebral atherosclerosis.

• Clinical pearl: The absence of symptoms does NOT indicate absence of significant atherosclerosis; many patients suffer their first cardiac event with no prior warning, underscoring the importance of risk stratification and preventive therapy.

• Fasting lipid panel: The gold standard includes total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides (calculated as total cholesterol − HDL − triglycerides/5). Should be obtained after 9-12 hour fast; non-fasting panels are now acceptable for LDL and total cholesterol estimation but triglycerides require fasting for accuracy.

• LDL particle number (LDL-P) and apolipoprotein B (apoB): More predictive of ASCVD risk than LDL-C alone, especially in patients with metabolic syndrome, type 2 diabetes, or discordant lipid results. Measured via nuclear magnetic resonance (NMR) spectroscopy; not yet standard but increasingly recognized as superior.

• Lipoprotein(a) [Lp(a)]: An independent ASCVD risk factor measured as a single value (not affected by statin therapy). Elevated Lp(a) (>50 mg/dL) markedly increases thrombotic and atherosclerotic risk and warrants intensified LDL-lowering therapy; measured once in adulthood for risk stratification.

• Screening and risk assessment: ATP III and ACC/AHA guidelines recommend lipid screening every 4-6 years starting at age 20; more frequent in those with ASCVD risk factors. 10-year ASCVD risk calculated using Framingham or pooled cohort equations guides intensity of treatment.

• Familial hypercholesterolemia (FH) diagnosis: Suspected in patients with LDL-C >190 mg/dL (untreated), personal or family history of premature ASCVD, xanthomas, or corneal arcus. Confirmed by genetic testing (heterozygous FH ~1:500, homozygous FH ~1:1,000,000); homozygous FH presents in childhood with severe atherosclerosis.

• Secondary dyslipidemia evaluation: Rule out hypothyroidism, nephrotic syndrome, cholestasis, and uncontrolled diabetes; these must be treated first as they may resolve the lipid abnormality.

• Important diagnostic consideration: Non-HDL cholesterol (total cholesterol − HDL) captures all apoB-containing particles and predicts risk better than LDL-C alone, particularly when triglycerides are elevated.

• Lifestyle modifications (foundational for all): Weight loss (5-10% body weight reduction), increased aerobic exercise (150 minutes/week moderate intensity), dietary changes (reduced saturated fat <7%, trans fats, increased fiber 10-25 g/day), smoking cessation, and moderation of alcohol. These reduce LDL by 15-30%, raise HDL by 3-9%, and lower triglycerides by 20-30%.

• Statins (first-line pharmacotherapy): HMG-CoA reductase inhibitors reduce LDL-C by 30-55%. High-intensity statins (atorvastatin 40-80 mg or rosuvastatin 20-40 mg daily) reduce ASCVD events by 20-30% and are indicated for all patients with established ASCVD, LDL >190 mg/dL, or 10-year ASCVD risk ≥7.5%. Moderate-intensity statins (simvastatin 20-40 mg, atorvastatin 10-20 mg) are used for primary prevention with lower risk. Side effects include muscle symptoms (myalgia/myopathy in 0.1-1%) and elevated transaminases; CK and liver enzymes need not be routinely monitored unless symptomatic.

Complications of atherosclerosis itself

• Acute coronary syndrome / MI (emergency): thin-cap plaque rupture exposes tissue factor and collagen → occlusive thrombus. Signals: ischemic chest pain with ST elevation, or dynamic ST-depression/T-wave changes with rising troponin. A new LBBB is not a stand-alone STEMI criterion — apply Sgarbossa criteria.
• Sudden cardiac death (emergency): ischemia-triggered ventricular fibrillation or pulseless VT — the shockable pair; immediate defibrillation.
• Ischemic stroke / TIA (emergency): carotid plaque rupture with artery-to-artery embolism; abrupt focal deficit, carotid bruit, non-contrast CT to exclude hemorrhage before thrombolysis.
• Peripheral arterial disease and acute limb ischemia (emergency): claudication progressing to rest pain, ulceration, ankle-brachial index below normal; the six Ps signal acute occlusion.
• Abdominal aortic aneurysm and acute mesenteric ischemia (emergencies): the abdominal aorta is the most common site of atherosclerosis; rupture presents with hypotension and pulsatile mass, mesenteric ischemia with pain out of proportion to exam.
• Ischemic cardiomyopathy and renovascular hypertension: chronic hypoperfusion → HFrEF (treated with the four pillars: ARNI or ACEI/ARB, beta blocker, MRA, SGLT2 inhibitor) or renal artery stenosis with flash pulmonary edema.
• Cholesterol embolization syndrome: days to weeks after catheterization or anticoagulation — blue toe syndrome, livedo reticularis, AKI, eosinophilia, and low complement.
• Acute pancreatitis (emergency): from severe hypertriglyceridemia, not from atheroma; suspect when triglycerides are extremely high and serum is lipemic.

Complications of therapy

• Statin-associated myopathy and rhabdomyolysis (emergency): reduced mevalonate/CoQ10 and myocyte injury; myalgias with markedly elevated CK, myoglobinuria, and AKI. Risk multiplies with CYP3A4 inhibitors (clarithromycin, azoles, amiodarone, verapamil) and with gemfibrozil — fenofibrate is the safer fibrate to combine.
• Statin hepatotoxicity and new-onset diabetes: transaminase elevation is usually mild; the small diabetes signal does not outweigh ASCVD benefit per the 2018 ACC/AHA guideline.
• Other agents: niacin causes prostaglandin-mediated flushing, hyperglycemia, and hyperuricemia; bile acid sequestrants raise triglycerides and bind fat-soluble vitamins and other drugs; fibrates cause gallstones and a reversible creatinine rise; PCSK9 inhibitors cause injection-site reactions.

• Foam cell = lipid-laden macrophage; fatty streak = earliest visible lesion: the sequence tested is endothelial injury → LDL oxidation → scavenger-receptor uptake → foam cell → fatty streak → fibrous plaque. The abdominal aorta is the most commonly involved vessel overall; the proximal LAD is the classic coronary site.
• Xanthoma type localizes the defect: Achilles/extensor tendon xanthomas → familial hypercholesterolemia (LDL receptor defect); palmar crease xanthomas → apoE2/E2 dysbetalipoproteinemia; eruptive xanthomas on buttocks with lipemic serum → chylomicronemia from LPL or apoC-II deficiency.
• Single best next step by scenario: established ASCVD or untreated LDL ≥190 mg/dL → high-intensity statin regardless of calculated risk (2018 ACC/AHA); diabetes age 40–75 → at least moderate-intensity statin (ADA Standards of Care and ACC/AHA agree); intermediate risk with genuine uncertainty → coronary artery calcium score to reclassify, with a score of zero favoring deferral.
• The association examiners love: elevated Lp(a) is genetically determined, unaffected by statins, and confers thrombotic plus atherogenic risk — the answer when premature ASCVD occurs despite a near-normal LDL.
• Triglycerides above roughly 400 mg/dL invalidate the Friedewald equation: order a directly measured LDL or use non-HDL cholesterol. Severe hypertriglyceridemia is treated first to prevent pancreatitis — fibrate plus very-low-fat diet, not a statin.
• Common distractor — chasing HDL: niacin added to statin therapy raises HDL but has not reduced cardiovascular events; do not select an HDL-raising drug as the outcome-improving choice.
• Common distractor — routine lab monitoring: check a baseline lipid panel and hepatic panel, then follow lipids for adherence; do not check CK or LFTs at every visit in an asymptomatic patient.
• Pregnancy: statins are generally discontinued during pregnancy and lactation and replaced by bile acid sequestrants if therapy is required; recall separately that all ACE inhibitors, including captopril, are contraindicated in pregnancy.