Monday, June 21, 2010

Is metabolic syndrome a useless construct?

Harriet Hall over at Science Based Medicine thinks it is:

The concept of a metabolic syndrome originally seemed promising: it carried the hope of better identifying patients at risk, contributing to establishing an etiology related to insulin resistance, and determining better routes to prevention and treatment. These ideas haven’t panned out. It is still unclear whether obesity causes the associated findings or whether an underlying condition causes the obesity along with the other findings or whether something else is going on. It is becoming increasingly clear that identifying and managing individual risk factors is the way to go.

Should the concept of metabolic syndrome be abandoned? Probably. But human nature makes us reluctant to abandon any idea after it has rooted itself in our consciousness. The metabolic syndrome has become so well established in the popular medical mind that it will not go without a struggle.

There's a lot of good information in the post but I must respectfully disagree with the conclusion. Although the syndrome's definition may be imprecise it is a metabolic stew of disorders that tend to cluster together and have important things in common regarding diagnosis and treatment.

So let's look at both sides of the debate. It's to be acknowledged that the genetics and the interrelationships among the metabolic disturbances are incompletely understood. There are lots of “which came first” and “true, true and maybe unrelated” type questions to be asked. And, though the tendency of these disorders to cluster together is very strong, there is evidence here and there demonstrating that some of these disorders occasionally (though not usually) behave as independent risk factors (e.g. LDL pattern B and insulin resistance).

On the other side of the debate, favoring recognition of the syndrome, are several facts. Metabolic syndrome is important to identify because affected patients don't do well with statin drugs as monotherapy. For this reason they need to be recognized so that their residual risk after statin therapy can be recognized and addressed. Widespread failure to do this in the US has resulted in untold events. Metabolic syndrome is uniquely amenable to treatment with diet and exercise---more so than most of the traditional “LDL disorders.” Drug therapy is specific and focuses on niacin, and sometimes fibrate drugs. As understanding of metabolic syndrome improves we may come up with better terminology and perhaps a categorization of affected patients. Exciting findings over the past decade suggest a “final common pathway” by which the disorders of the metabolic syndrome operate, and maybe a unifying hypothesis: impairment of reverse cholesterol transport.

There are two classic review articles that are must-read for anyone with an interest in this topic. They point to primary sources of information for all the points I've raised and can be accessed here and here.

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