Positron Emission Tomography (PET) Detects Lymph Node Activation During HIV Infection

Positron emission tomography (PET) can detect lymphoid tissue activation that seems to occur in a predictable pattern as the disease progresses, two research teams report in September 20th issue of The Lancet.

These findings suggest that PET imaging could be used to clinically stage patients infected with HIV. They also have implications for possible surgical or radiological treatment of lymph nodes as an option, in addition to antiretroviral therapy, for HIV disease management.

The imaging strategy is based on the knowledge that resting lymphocytes increase their glucose uptake when they become activated. The change in uptake can be monitored by using fluorine-18-labelled fluorodeoxyglucose (FDG), with PET scanning conducted 45 minutes after intravenous infusion.

In the first report, Dr. David H. Schwartz and colleagues at Johns Hopkins University, Baltimore, enrolled 12 patients recently infected and 11 chronically infected with HIV. All subjects were asymptomatic and underwent FDG-PET imaging.

Both groups of patients exhibited node activation that was greater in the neck and upper torso than in the lower torso. The authors also observed "extremely tight" correlation between viraemia and net lymphoid PET signal in both groups. The slopes of linear regression lines were also similar.

However, nodes did not show up on PET in patients with undetectable viral loads.

Dr. Schwartz's group suggests that loci of persistent activation could be surgically removed. Even though latent virus would remain, they maintain, "re-activation might not occur for months or years after removal...thereby allowing extended interruptions of treatment."

In the second report, Dr. C. David Pauza, also at the University of Maryland Biotechnology Institute in Baltimore, and his team examined FDG-PET scans from 15 HIV-infected patients at various stages of infection.

Lymphoid activation was highest in the head and neck during acute disease, they note. At mid-stages, there was a generalized pattern of peripheral lymph-node activation. Late-stage disease was associated with activation in mesenteric lymph nodes and around the ileocaecal junction.

In two patients with CDC stage C3 disease, FDG uptake was negligible in peripheral lymph nodes and spleen, but was increased in bowel and the ileocaecal junction. Thus, "the ileocaecal region...could be the last major virus reservoir," Dr. Pauza's group suggests.

"We are now considering physical interventions for HIV disease progression" based on PET scan results, Dr. Pauza said. If small amounts of tissue that seem to be highly activated after antiretroviral therapy can be identified, they might be ablated with radiation or removed surgically.

9/22/03

Lancet 2003;362: 945-950, 959-961.