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Dyslipidemia-2

7 min read

Dyslipidemia: Pathophysiology, Diagnosis & Management

Dr. Eatimad Mahgoub Osheik
Assistant Professor, MD Internal Medicine

Learning Objectives

  • Define dyslipidemia
  • Understand lipid metabolism
  • Interpret lipid profile
  • Identify ASCVD risk
  • Apply ACC/AHA guidelines
  • Choose appropriate therapy

Background

  • Lipids are organic water non soluble molecules
  • Major types include:
    • Triglycerides: serving as long term energy store
    • Phospholipids: key component of cell membrane
    • Cholesterol: vital for building cells, producing hormones (like estrogen, testosterone, vitamin D), and making bile for digestion and brain development
  • Cholesterol and triglycerides are carried in the bloodstream by spherical particles called lipoproteins

What is Lipoprotein?

A lipoprotein is a complex particle made of lipids like cholesterol, triglycerides and a protein that acts as the body’s transport system for these fats through the bloodstream to cells.

Structure and Function

  • Core: Contains fats like triglycerides and cholesterol
  • Outer Shell: Composed of phospholipids and special proteins called apolipoproteins (like ApoB for LDL, ApoA-I for HDL)
  • Function: To carry fats to and from cells throughout the body

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Lipid Metabolism: Lipoprotein Types

  • Chylomicrons
  • VLDL (Very Low-Density Lipoprotein)
  • IDL (Intermediate-Density Lipoprotein)
  • LDL (Low-Density Lipoprotein)
  • HDL (High-Density Lipoprotein)

Major Types, Density, and Size

  • Chylomicrons: Largest and least dense, transport dietary fats from the gut
  • VLDL: Large, low density, carries triglycerides from the liver
  • IDL: Medium, intermediate density, derived from VLDL
  • LDL: Smaller, delivers cholesterol to tissues
  • HDL: Smallest, removes cholesterol from tissues, “good” cholesterol

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Lipid Metabolism Pathway

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Introduction to Dyslipidemia

  • Dyslipidemia = abnormal lipid levels in the blood
  • Consequence of abnormal lipoprotein metabolism
  • Major modifiable risk factor for ASCVD
  • Strong association with:
    • Coronary artery disease
    • Stroke
    • Peripheral arterial disease

Dyslipidemia Types

Includes:

  • ↑ Low Density Lipoprotein (LDL)
  • ↓ High Density Lipoprotein (HDL)
  • ↑ Triglycerides (TG)
  • Mixed dyslipidemia

Classification of Hyperlipidemia

Primary Hyperlipidemia

Single or multiple gene defect results in disturbance of LDL, HDL or/and TG production or clearance

Fredrickson Classification:

  • Type I: Familial Chylomicronemia
  • Type IIa: Familial Hypercholesterolemia
  • Type IIb: Familial Combined Hyperlipidemia
  • Type III: Dysbetalipoproteinemia
  • Type IV: Hypertriglyceridemia
  • Type V: Mixed Chylomicronemia-VLDL Elevation

When to Suspect Primary Hyperlipidemia

  • Early onset hyperlipidemia (childhood or young adulthood)
  • Strong family history of premature cardiovascular disease
  • Very high lipid levels:
    • LDL-C ≥190 mg/dL
    • Triglycerides ≥500 mg/dL
  • Poor response to diet and lifestyle changes
  • No secondary cause
  • Characteristic signs: tendon xanthomas, xanthelasma, corneal arcus at young age

Clinical Signs of Primary Hyperlipidemia

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Secondary (Acquired) Hyperlipidemia

Causes:

  • Endocrine causes: diabetes mellitus, hypothyroidism, obesity
  • Renal disease: nephrotic syndrome, chronic renal failure
  • Hepatic dysfunction: cholestasis
  • Medications: thiazide diuretics, β-blockers, oral estrogens, steroids
  • Lifestyle factors: excessive alcohol intake, high fat and carbohydrate diets, smoking

Lipid Profile Interpretation

Normal Values

ParameterNormal Value
Total Cholesterol< 200 mg/dL
LDL< 100 mg/dL
HDL> 40 mg/dL (men), > 50 mg/dL (women)
Triglycerides< 150 mg/dL

ASCVD Risk Factors

Nonmodifiable

  • Age (men ≥45 y; women ≥55 y)
  • Male sex
  • Family history of premature ASCVD
  • Race/ethnicity

Modifiable

  • Dyslipidemia
  • Hypertension
  • Diabetes mellitus
  • Smoking
  • Obesity/metabolic syndrome

ASCVD: Key Concept

ASCVD includes:

  • Coronary artery disease
  • Cerebrovascular disease; Stroke / TIA
  • Peripheral arterial disease

ACC/AHA focuses on ASCVD risk, not LDL alone

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Lipid-Lowering Therapies Summary

ClassExamplesPrimary EffectUse CaseCommon Side Effects
StatinsAtorvastatin, Rosuvastatin↓ LDL, ↓ TG, ↑ HDLFirst-line for high CV riskMuscle pain, liver enzyme elevation
EzetimibeEzetimibe↓ LDLAdd-on to statins or statin-intolerantGI upset, rare liver effects
PCSK9 InhibitorsEvolocumab, Alirocumab↓↓↓ LDLHigh-risk, familial hypercholesterolemiaInjection site reactions
Bempedoic AcidBempedoic acid↓ LDLStatin-intolerant patientsHyperuricemia, tendon rupture
FibratesFenofibrate, Gemfibrozil↓ TG, ↑ HDLSevere hypertriglyceridemiaMyopathy (esp. with statins), GI upset
Omega-3 Fatty AcidsIcosapent ethyl (Rx fish oil)↓ TGHigh triglycerides, CV risk reductionGI upset, bleeding risk
NiacinNiacin↓ LDL, ↓ TG, ↑ HDLRarely used now due to side effectsFlushing, liver toxicity

Statins: Mechanism of Action

  • Inhibit HMG-CoA reductase (Hydroxy Methyl Glutaryl-CoA reductase) → ↓ cholesterol synthesis in liver
  • Liver compensates by ↑ LDL receptor expression → ↑ LDL clearance from blood
  • Result: ↓ LDL (primary), modest ↓ TG, slight ↑ HDL

Side Effects & Management

  • Muscle pain/myopathy → check CK, reduce dose, switch statin, or try alternate-day dosing
  • Rhabdomyolysis (rare) → stop statin, hospitalize, hydrate
  • Elevated liver enzymes → monitor AST/ALT, stop or reduce dose if >3× ULN
  • GI upset → take with food, at night
  • Drug interactions

Statin Intensity Categories

High-Intensity (↓ LDL ≥50%)

  • Atorvastatin 40–80 mg
  • Rosuvastatin 20–40 mg

Moderate-Intensity (↓ LDL 30–49%)

  • Atorvastatin 10–20 mg
  • Rosuvastatin 5–10 mg
  • Simvastatin 20–40 mg

Management According to ACC/AHA Guidelines

Initial Evaluation (All Patients)

A. Fasting or Non-fasting Lipid Panel

  • Total cholesterol
  • LDL-C
  • HDL-C
  • Triglycerides

B. Identify Secondary Causes, Review Medications

C. Assess ASCVD Risk

  • Use Pooled Cohort Equations (age 40-75)
  • 10-year ASCVD risk categories:
    • Low: <5%
    • Borderline: 5-7.4%
    • Intermediate: 7.5-19.9%
    • High: ≥20%

Lifestyle Measures (All Patients)

  • Heart-healthy diet (Mediterranean/DASH; Dietary Approaches to Stop Hypertension)
  • Weight reduction
  • Physical activity (≥150 min/week)
  • Smoking cessation
  • Limit alcohol

Statin Benefit Groups (ACC/AHA)

Statins recommended for 4 major groups:

  1. Clinical ASCVD
  2. LDL ≥ 190 mg/dL
  3. Diabetes (age 40–75)
  4. High ASCVD risk (≥7.5%)

Clinical ASCVD Management

Includes:

  • Prior MI, stroke/TIA
  • PAD
  • Coronary or arterial revascularization

Management:

  • High-intensity statin:
    • Atorvastatin 40–80 mg
    • Rosuvastatin 20–40 mg

Goals:

  • ≥50% LDL-C reduction
  • LDL-C <70 mg/dL (practical target)

If LDL ≥70 despite max statin:

  • Add ezetimibe
  • If still ≥70 → PCSK9 inhibitor

Severe Hypercholesterolemia Management

LDL-C ≥190 mg/dL (age 20–75)

Initial Management:

  • High-intensity statin (no risk calculation needed)

If LDL ≥100:

  • Add ezetimibe
  • Consider PCSK9 inhibitor (esp. familial hypercholesterolemia)

Diabetes Mellitus Management (Age 40–75, LDL ≥70)

Management:

  • Moderate-intensity statin (minimum)
  • High-intensity statin if:
    • Age 50–75
    • Multiple ASCVD risk factors

Primary Prevention (No ASCVD, No DM, LDL 70-189)

Based on 10-year ASCVD Risk:

  • Borderline (5-7.4%): Consider statin if risk enhancers present
  • Intermediate (7.5-19.9%): Moderate-intensity statin
  • High (≥20%): High-intensity statin

Risk-Enhancing Factors (Help Decide Statin Use)

  • Family history of premature ASCVD
  • LDL ≥ 160 mg/dL
  • Metabolic syndrome
  • CKD
  • Chronic inflammatory diseases
  • South Asian ethnicity
  • Elevated TG ≥ 175 mg/dL
  • hs-CRP ≥ 2 mg/L
  • Lp(a), ApoB elevation

Hypertriglyceridemia Management

TG <5.6 mmol/L (150-499 mg/dL)

  • Statins first-line for ASCVD risk reduction
  • Consider icosapent ethyl (EPA) in high-risk patients on statins
  • Fibrates not routine

TG ≥5.6 mmol/L (≥500 mg/dL)

  • Goal: prevent pancreatitis
  • Fibrate first-line
  • Add omega-3 fatty acids
  • Statin if ASCVD risk present

TG ≥11.3 mmol/L (≥1000 mg/dL)

  • Very high pancreatitis risk
  • Very low-fat diet, strict glucose control
  • Hospitalize if symptomatic

General Management Flowchart

Patient with Dyslipidemia
        ↓
Fasting Lipid Profile
        ↓
Rule out Secondary Causes (DM, Hypothyroidism, CKD, Drugs)
        ↓
Lifestyle Modification (ALL PATIENTS)
        ↓
Assess ASCVD Risk / Statin Benefit Group
        ↓
Start Statin Therapy (if indicated)
        ↓
Reassess Lipids after 4-12 weeks
        ↓
   Target Achieved?
    ↙         ↘
   YES        NO
    ↓          ↓
Continue  ↑ Statin Intensity or Add Ezetimibe
Statin              ↓
            Consider PCSK9 inhibitor (very high risk)

ACC/AHA-Based Statin Decision Algorithm

Does patient have Clinical ASCVD?
            ↓
    YES → High-intensity statin
            ↓
           NO
            ↓
Is LDL ≥190 mg/dL?
            ↓
    YES → High-intensity statin
            ↓
           NO
            ↓
Is patient diabetic (Age 40–75)?
            ↓
YES → Moderate / High-intensity statin
            ↓
           NO
            ↓
Calculate 10-year ASCVD risk
            ↓
Risk ≥7.5% → Moderate / High-intensity statin
Risk <7.5% → Lifestyle modification

Hypertriglyceridemia Management Summary

Triglycerides Level
        ↓
<150 mg/dL → Normal
150–499 mg/dL → Lifestyle + Statin (if ASCVD risk)
≥500 mg/dL → Fibrate ± Omega-3
        ↓
Prevent Acute Pancreatitis

Clinical Scenarios

Scenario 1

Patient: 62-year-old male, history of MI 2 years ago

Lipid profile:

  • Total cholesterol: 220 mg/dL
  • LDL-C: 150 mg/dL
  • HDL-C: 35 mg/dL
  • TG: 150 mg/dL

Scenario 2

Patient: 35-year-old female, no ASCVD, family history of premature CAD

Lipid profile:

  • Total cholesterol: 330 mg/dL
  • LDL-C: 250 mg/dL
  • HDL-C: 40 mg/dL
  • TG: 150 mg/dL

Scenario 3

Patient: 50-year-old male, type 2 diabetes, no ASCVD

Lipid profile:

  • Total cholesterol: 210 mg/dL
  • LDL-C: 130 mg/dL
  • HDL-C: 38 mg/dL
  • TG: 180 mg/dL

Scenario 4

Patient: 45-year-old female, no ASCVD, non-diabetic, borderline 10-year ASCVD risk 7%

Lipid profile:

  • Total cholesterol: 210 mg/dL
  • LDL-C: 140 mg/dL
  • HDL-C: 50 mg/dL
  • TG: 150 mg/dL

Scenario 5

Patient: 40-year-old male, presents for routine check-up, BMI 32

Lipid profile:

  • Total cholesterol: 250 mg/dL
  • LDL-C: 120 mg/dL
  • HDL-C: 35 mg/dL
  • TG: 800 mg/dL

Summary

  • Dyslipidemia is a major, modifiable cause of ASCVD
  • LDL-C is the primary treatment target
  • Statins are first-line therapy
  • Lifestyle modification is essential for everyone
  • Risk stratification guides therapy
  • Add non-statins when needed
  • Triglycerides matter → pancreatitis risk
  • Treat secondary causes first

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