The researchers also attempted to establish an objective threshold, based on PET imaging, for determining which participants were amyloid-positive and which were amyloid-negative.
Previous studies have given mixed results as to whether amyloid deposition is associated with poorer, albeit not clinically significant, cognitive function. One of the issues in such research was the lack of a consistent threshold for defining amyloid positivity. In the earlier studies, Dr. Klunk explained, “thresholds were vaguely defined and were often subjective in nature. This study used an objective statistical approach to clearly define a standard threshold.”
The researchers used Pittsburgh Compound B (PiB) as a PET imaging agent and applied a graphical analysis to estimate regional PiB retention distribution volume, ultimately to yield distribution volume ratios. The study cohort consisted of 43 volunteers with a mean age of 74.4 and a mean of 15.1 years of education. None were cognitively impaired, according to a battery of neuropsychologic screening tests, although a family history of dementia was not an exclusion criterion. Following the initial screening, the participants underwent additional cognitive assessments, including tests of cognitive reserve, information-processing speed, working memory, and inhibitory efficiency.
Based on quantitative boundaries developed with a separate group of cognitively normal subjects, the researchers categorized nine of the 43 participants (21%) as amyloid-positive, 29 (67%) as amyloid-negative, and the remaining 5 (12%) as intermediate. Neurocognitive performance was not significantly worse among amyloid-positive participants than among those who were amyloid-negative.
The results suggest that “in a significant number of elderly, cognitively normal persons, amyloid accumulation does not impair cognitive function,” the investigators concluded.
Arch Neurol. 2008;65(11):1509-1517.
Fever Affects Stroke Outcomes
NEW YORK, November 28 (Reuters Health)—Fever is consistently associated with a worse outcome in patients with stroke or other neurologic injury, according to results of a comprehensive meta-analysis. “Many studies associate fever with poor outcome in patients with neurologic injury, but this relationship is blurred by divergence in populations and outcome measures,” noted Dr. David M. Greer from Massachusetts General Hospital in Boston, and colleagues in the November Stroke.
In their pooled analyses covering 39 relevant studies and a total of 14,431 patients with stroke and other brain injuries, fever or higher body temperature was consistently and significantly associated with worse outcome in every measure studied, they reported.
Specifically, fever or higher body temperature increased the risk of death, neurologic deficit, more dependence, lower functioning, greater severity, longer ICU stay, and longer hospital stay, with relative risks of 1.5, 1.3, 1.9, 2.2, 1.4, 2.8, and 3.2, respectively. These findings indicate that “fever in patients with neurologic injury is a condition of clinical importance,” Dr. Greer and colleagues concluded.
Stroke. 2008;39(11):3029-3035.