Department of Internal Medicine, Federal Medical Center, Ido-Ekiti, Ekiti State, Nigeria.
A cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, which occur together have become known as the metabolic syndrome. Over the years various diagnostic criteria have been proposed by different organizations and most recently efforts have been made to unify the diagnostic criteria. This article is aimed at providing an overview of the metabolic syndrome and a rational approach to the management of this very important clinical syndrome.
Dr. A.O Oladejo
Department of Internal Medicine
Federal Medical Center
Ekiti State, Nigeria
INTRODUCTION AND HISTORICAL BACKGROUND
The concept of the metabolic syndrome has existed for at least 80 years1. It was first described by Kylin, a Swedish Physician, as the clustering of hypertension, hyperglycemia, and gout2. Later, in 1947, Vague drew attention to upper abdominal adiposity (android or male-type obesity) as the obesity phenotype that was commonly associated with type 2 diabetes mellitus and cardiovascular disease3.
The field moved forward significantly following the 1988 Banting lecture given by Gerald Reaven. He described a cluster of risk factors for diabetes and cardiovascular disease comprising hypertension, hyperglycemia, low high-density lipoprotein (HDL) cholesterol, and raised very low-density lipoprotein (VLDL) triglyceride and named it Syndrome X. His main contribution was the introduction of the concept of insulin resistance4.
The metabolic syndrome is also known as Syndrome X, the insulin resistance syndrome, cardio-metabolic syndrome, dysmetabolic syndrome and the deadly quartet syndrome5,6 .The constellation include glucose intolerance (type 2 diabetes, impaired fasting glucose, or impaired glucose tolerance), insulin resistance, central obesity, dyslipidemia, and hypertension, all well documented risk factors for cardiovascular diseases. The metabolic syndrome is associated with an increased risk for the development of type 2 diabetes mellitus and cardiovascular disease. People with the syndrome are twice as likely to die from a macrovascular event and three times as likely to have ischemic heart disease and stroke compared with people without the syndrome7. The syndrome is affecting the general population in epidemic proportion and is frequently associated with increased risk of cardiovascular morbidity and mortality8,9.
Over the past two decades, a striking increase in the number of people with the metabolic syndrome worldwide has taken place. This increase is associated with the global epidemic of obesity and diabetes. With the elevated risk not only of diabetes but also of cardiovascular disease from the metabolic syndrome, there is an urgent need for strategies to prevent the emerging global epidemic10, 11.
In the United States, the metabolic syndrome is emerging as a major public health problem. Between 1988-1994 and 1999-2000, the age adjusted prevalence of the metabolic syndrome increased dramatically among women (23.5%) and only slightly among men (2.2%). An estimated 55 million adults in the United States had the syndrome in 2000. The age adjusted prevalence was 31.9% among Mexican Americans, 23.8% among non-Hispanic whites, and 21.6% among African Americans12, 13.
The prevalence of the metabolic syndrome among a multi-ethnic population of 1276 men and women from four communities in Canada was 25.8% 14. The prevalence in a population based cohort of 1565 individuals with diabetes in Italy was 75.6% 15. A study done in Oman showed a prevalence of 23.0% in women and 19.5% in men16. The prevalence of the metabolic syndrome among healthy elderly Southwestern Nigerians was 35% 17 while a study done in Benin, Nigeria using three diagnostic tools – World Health Organization (WHO), Adult Treatment Panel (ATPIII) and International Diabetes Federation (IDF) criteria revealed a prevalence of 33.4%, 22.6% and 30.9% respectively18.
Clinical Diagnosis of Metabolic Syndrome
Many investigations confirm that multiple cardiovascular risk factors of endogenous origin commonly aggregate in one individual. Although the metabolic syndrome is often referred to as a discrete entity, it is important to recognize it as a syndrome and not a defined uniform entity. No single pathogenesis has been elucidated but the syndrome could range from a cluster of unrelated risk factors to a constellation of risk factors linked through a common underlying mechanism.
In the effort to introduce the metabolic syndrome into clinical practice, several organizations have attempted to formulate simple criteria for its diagnosis. The first proposal came in 1998 from a consultation group on the definition of diabetes for the World Health Organization. This group emphasized insulin resistance as the major underlying risk factor and required evidence of insulin resistance for diagnosis19
In 1999, the European group for the Study of Insulin Resistance (EGIR) proposed a modification of the WHO definition. This group used the term insulin resistance syndrome rather than metabolic syndrome20. In 2001, the National Cholesterol Education Program (NCEP) Adult Treatment Panel III (ATP) introduced alternative clinical criteria for defining the metabolic syndrome. In so doing, the purpose of ATPIII was to identify people at higher long-term risk for arterosclerotic vascular disease (ASCVD) who deserved clinical and lifestyle modification to reduce risk21.