Pulmonary hypertension is divided into two forms. When the condition occurs in people without a disease known to cause it, doctors call it primary pulmonary hypertension. When it is the result of other health conditions, such as heart problems, lung diseases, or autoimmune disorders, it is called secondary pulmonary hypertension. In this case, the underlying cause is the primary condition. Pulmonary hypertension is the secondary result.

Primary pulmonary hypertension (PPH) is a very rare condition, striking only one to two out of every 1 million people. An estimated 300 Americans are diagnosed with primary pulmonary hypertension every year.

Researchers do not know what causes primary pulmonary hypertension. One reason it remains a mystery is that it affects so few people. Its rarity makes it difficult for scientists to learn more about it. In the last four decades, two puzzling outbreaks of pulmonary hypertension led medical sleuths to a surprising suspect: appetite suppressants. Between 1967 and 1973, the number of recorded cases of pulmonary hypertension jumped tenfold in Europe. Medical detectives traced the outbreak to a weight-loss drug called aminorex fumarate, which was introduced in 1965 in Europe. When the drug was withdrawn, the number of cases fell. More recently, health experts in the United States detected another spike in cases of primary pulmonary hypertension. The epidemic was traced to two new prescription weight-loss drugs, fenfluramine and dexfenfluramine. Both have since been withdrawn from the market.

Some experts speculate that people who develop the disease have blood vessels that are abnormally sensitive to certain factors. Cocaine use, the HIV virus, pregnancy, and the diet drugs noted above are among the suspected factors, but there are no doubt others. In some people, these factors may make the lining of the pulmonary arteries particularly susceptible to damage. However, most people with these factors don't go on to develop pulmonary hypertension.

Interestingly, primary pulmonary hypertension was originally described as a disease without a known cause, but since that time many different factors have been associated with it. Appetitite suppressants are most clearly associated with PPH, and the World Health Organization, aiming to make this issue more clear, calls this condition "pulmonary arterial hypertension" related to diet drugs. It is, however, indistinguishable from PPH except that people who have it also have a history of taking diet drugs.

Why some people are at increased risk is largely unknown. PPH usually shows up between the ages of 30 and 50. Women are at significantly higher risk than men. Why women are more susceptible also remains a puzzle.

The genetic link to this mystifying illness is better known. Scientists have learned, for example, that primary pulmonary hypertension sometimes runs in families. Experts estimate that about 6 percent of newly identified cases of PPH occur in families where at least one other person suffers from the disease. Researchers have identified the gene involved, which is called BMPR2. Because of the family connection, doctors often recommend that other close relatives of the family be tested when one person has been diagnosed with primary pulmonary hypertension. But inherited PPH is exceedingly rare. Fewer than 100 families in the United States have been found in which the disease has occurred in at least two first-degree relative (parent, child, sibling). The likelihood of a first-degree relative being affected when only one person in the family is known to have primary pulmonary hypertension is estimated to be 0.6 to 1.2 percent, according to a WHO-sponsored world symposium on PPH.

Research into the genetic factors linked to PPH has begun to offer clues about what may cause the disease. Mutations of the BMPR2 gene interrupt normal signals to cells in blood vessel linings, causing them to multiply abnormally. In turn, the inner walls and the smooth muscles of pulmonary arteries thicken, researchers speculate. Scarring, or fibrosis, can also occur.

Because primary pulmonary hypertension is diagnosed when doctors are unable to identify other medical conditions that might be causing the high blood pressure in pulmonary arteries, it remains a difficult disease to treat. Physicians can try to alleviate the symptoms and ease the strain on the heart and lungs by lowering the pulmonary blood pressure.

Secondary pulmonary hypertension is far more common than PPH. Because it frequently goes undiagnosed, researchers don't know precisely how many people suffer from secondary pulmonary hypertension. Most cases are only recognized when the symptoms become serious enough for people to seek medical attention.

Causes of secondary pulmonary hypertension can include autoimmune disorders such as lupus or scleroderma, congenital heart disease, valvular or left ventricular heart disease, chronic liver disease, HIV/AIDS, emphysema, pulmonary fibrosis, blood clots in pulmonary arteries, sickle cell disease, and other conditions. In some cases, doctors can treat the underlying problem and reduce blood pressure in the pulmonary arteries. In others, they treat the symptoms of elevated pulmonary pressure.

-- Peter Jaret is a contributing editor for Health magazine and a winner of the American Medical Association's award for medical reporting. His work has appeared in National Geographic, Newsweek, Hippocrates, and many other national magazines. He is also the author of In Self-Defense (Harcourt Brace Jovanovich), Active Living Every Day, and Heart Healthy for Life.

References

The Rush Heart Institute Center for Pulmonary Heart Disease, www.rush.edu

First published October 28, 2003
Last updated October 30, 2007
Copyright © 2003 Consumer Health Interactive

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