COLUMBUS, Ohio - Smokers who test positive for the human immunodeficiency virus (HIV), the virus that causes AIDS, may be up to seven times more likely to develop emphysema, new research suggests.
The findings have important implications for the health of people with HIV, and they may also help doctors understand the cause of emphysema in smokers generally.
Emphysema is a chronic, debilitating lung disease that strikes some long-term smokers. Advanced emphysema results in breathlessness following even minor exertion.
The disease usually strikes people who are in their 50s and 60s, but in this study, early emphysema was detected in people with an average age of 35.
"Our results show that HIV-positive smokers, even before they develop other complications like pneumonias, appear to have a much higher risk of smoking-related lung damage," said Philip Diaz, associate professor of internal medicine and a member of Ohio State University's Heart and Lung Institute.
The study, conducted by Diaz and a team of researchers, was published in a recent issue of the Annals of Internal Medicine. It involved 114 HIV-positive smokers and 44 HIV-negative controls matched for age and smoking history. None of the HIV-positive smokers were hospitalized or experiencing infection-related complications.
Evidence of emphysema was based on high-resolution computerized tomography (CT) scans.
The results showed early signs of emphysema in 15 percent (17 of 114) of the HIV-positive smokers and in 2 percent (1 of 44) of the HIV-negative smokers.
The results were more pronounced for HIV-positive smokers with a history of 12-pack years or more of smoking (i.e., a pack a day for 12 years). Here, 37 percent (14 of 38 people) of the HIV-positive group showed signs of emphysema; no cases were found among 14 people in the control group.
However, most of the participants were studied prior to 1998, before the widespread availability of protease inhibitors which are often effective in controlling AIDS symptoms. Thus, only 10 percent of the HIV-positive smokers in the study were using the life-prolonging, highly active antiretroviral therapy (HAART), which is the standard of care today.
Because HAART prolongs life it may offer some protection from the onset of emphysema in HIV-positive smokers, a possibility borne out by some preliminary data gathered by Diaz and the team of researchers.
"On the other hand, people on HAART are living longer, so emphysema could remain a problem for them," he said. "But that's speculation.
"I think until proven otherwise, our study supports the concept that people with this chronic viral infection are more predisposed to adverse effects of cigarette smoking. It makes it all the more important for physicians to encourage people who are HIV positive to quit smoking."
The findings also revealed a higher level of cytotoxic lymphocytes (CTLs) in fluids rinsed from the lungs of the HIV-positive smokers. This suggests that CTLs could play an important role in the development of the disease, something that scientists still understand poorly even in the general populations of smokers.
This research supports a relatively new theory that links the destruction of lung tissue occurring during emphysema to the work of CTLs. CTLs destroy cells that are infected by virus. "Some people think what separates the smokers who get emphysema from those who don't might be a viral infection that's been latent in their lungs and that activates CTLs," said Diaz. "Our observations support that hypothesis."
Recent biopsy studies of people with emphysema from the general population also show that CTLs could be important.
Diaz and his team are now studying the lungs of people who have died of HIV for evidence of viral infection in the lungs. Diaz's study was funded by a grant from the National Heart, Lung, and Blood Institute.