Metabolic syndrome

Definition

Metabolic syndrome refers to the combined occurrence of abdominal (visceral) obesity, arterial hypertension, impaired glucose metabolism or insulin resistance and dyslipidemia. It identifies people at markedly increased risk of type 2 diabetes and atherosclerotic cardiovascular disease. Synonyms are syndrome X and insulin resistance syndrome.

Classification

Diagnostic criteria

Several definitions exist. According to the definition given in the German National Care Guideline (NVL) on type 2 diabetes, metabolic syndrome is present when three of five criteria are met:

• Central obesity: waist circumference ≥ 102 cm in men, ≥ 88 cm in women (values for people of European origin)
• Triglycerides: ≥ 150 mg/dl (1.7 mmol/l)
• Low HDL cholesterol: men < 40 mg/dl (1.0 mmol/l), women < 50 mg/dl (1.3 mmol/l)
• Blood pressure: systolic ≥ 130 mmHg and/or diastolic ≥ 85 mmHg
• Fasting glucose: ≥ 100 mg/dl (5.6 mmol/l)

A value already lowered by drugs counts as a fulfilled criterion in each case. For other ethnic groups, lower waist thresholds are used in part.

Occurrence & epidemiology

The frequency of metabolic syndrome parallels that of obesity and type 2 diabetes and increases with age. In a US survey it was about 23 % in the general population, 44 % in people aged 60 to 69 and 42 % in those aged 70 and over. Children and adolescents can also be affected; there is no uniform definition for these age groups.

Aetiopathogenesis

Besides the amount, the distribution of adipose tissue is decisive: central (visceral) obesity with a high waist-to-hip ratio ("apple shape") increases the risk, whereas fat distributed around the hips and thighs ("pear shape") does so much less.

• Visceral fat delivers increased free fatty acids via the portal vein; fat accumulates in the liver and in muscle cells.
• Insulin resistance with a compensatory increase in insulin secretion develops, leading to impaired glucose metabolism, dyslipidemia and hypertension.
• Uric acid is often raised; there is a prothrombotic state (increased fibrinogen and PAI-1) and a chronic inflammatory state.
• Smoking raises triglycerides and lowers HDL cholesterol; chronic stress may contribute through hormonal changes.

Clinical features

Metabolic syndrome itself usually causes no symptoms; clinically, central obesity is noticeable, sometimes with acanthosis nigricans as a skin sign of insulin resistance. The associated diseases and complications are important:

• type 2 diabetes and prediabetes
• atherosclerotic cardiovascular disease (coronary artery disease, stroke, peripheral artery disease)
• metabolic dysfunction-associated steatotic liver disease (MASLD)
• hyperuricemia and gout
• polycystic ovary syndrome in women, low testosterone and erectile dysfunction in men

Diagnosis

• History: family history of type 2 diabetes and cardiovascular disease, smoking, physical activity
• Physical examination: waist circumference, weight and body mass index, blood pressure; skin signs of insulin resistance
• Laboratory tests: fasting glucose (possibly HbA1c), lipid profile with triglycerides and HDL cholesterol; additionally uric acid and liver enzymes
• Imaging: liver ultrasound if steatosis is suspected

Waist circumference predicts the risk of metabolic and cardiovascular complications better than body mass index.

Keep learning in the app

Further reading (open access)

1. MSD Manual Professional: Metabolic Syndrome
2. NVL Typ-2-Diabetes: Anhang 5 Diagnosekriterien metabolisches Syndrom
3. MSD Manual Professional: Obesity
4. MSD Manual Professional: Type 2 Diabetes Mellitus

Cross-references