Decline in Platelet Count Precedes Onset of HIV Dementia

September 11, 2007

BALTIMORE -- The development of HIV-related dementia within the ensuing six or 12 months appears to be signaled by a sharp decline in platelet count, researchers said here.

BALTIMORE, Sept. 11 -- The development of HIV-related dementia within the ensuing six or 12 months appears to be signaled by a sharp decline in platelet count.

The finding, from a prospective cohort study of 146 HIV patients, offers an easily measured marker for HIV dementia, which accounts for about 5% of AIDS-defining illnesses in the U.S., reported Lynn Wachtman, D.V.M., of Johns Hopkins, and colleagues, in the September issue of Archives of Neurology.

But it is less clear what changes should be made in clinical management, wrote Dr. Wachtman and colleagues.

Although there was "a clear decline in median platelet count change from baseline to just before diagnosis" of HIV-related dementia in the study cohort, the researchers said, trends for individuals were less clear.

The researchers studied a subset of the North East AIDS Dementia (NEAD) cohort, a multi-center group of 396 patients with advanced HIV and low CD4 counts. They have been followed over time with serial neurologic, neuropsychological, functional, and psychiatric evaluations.

The researchers included only the 146 participants in this study who did not have HIV-related dementia at baseline or at their next follow-up visit (although they could have minor cognitive or motor disorder). For inclusion they also had to have had at least two follow-up visits.

Over a median follow-up of 31.1 months, 40 patients (27.4%) developed dementia. In addition, 65 (44.5%) had been diagnosed with minor cognitive or motor disorder at baseline.)

A univariate analysis found that baseline minor cognitive or motor disorder was significantly associated (P=0.03) with the likelihood of developing dementia. The hazard ratio was 2.01, with a 95% confidence interval from 1.06 to 3.78.

The primary variables of interest, however, were platelet count and hemoglobin levels, either lagged by one study visit or as an immediate marker.

Compared to a reference group whose platelets dropped by no more than 21,000 per microliter from baseline, those with a greater decline were at twice the risk of a diagnosis of dementia at the next study visit. The adjusted hazard ratio was 2.39, with a 95% confidence interval from 1.14 to 5.02, which was significant at P=0.02.

However, hemoglobin levels - measured at the visit before a diagnosis of dementia - were not significantly associated with increased risk.

On the other hand, platelet levels, measured at the same time as the dementia diagnosis, were no longer significantly associated with increased risk, while the opposite was true for hemoglobin.

Compared to a reference group with normal levels, low hemoglobin - defined as 2.7 to 12.6 grams per deciliter of blood - was significantly associated with dementia. The adjusted hazard ratio was 2.60, with a 95% confidence interval from 1.31 to 5.17, which was significant at P=0 .006.

Interestingly, the relationship between platelet level and dementia risk appeared to change over time, the researchers found. Specifically:

  • During the first two years of follow-up, a platelet decline at the visit immediately before a diagnosis of dementia was associated with an even greater risk of dementia, compared to those whose platelet counts were stable. The adjusted hazard ratio was 6.76 with a 95% confidence interval from 2.36 to 19.41, which was significant at P