Alzheimer's disease patients with depression showed slower decline in some behavioral measures than other patients did in a new study, a finding researchers say was a surprise.

It may mean that depression signals a form of Alzheimer's that follows a more benign behavioral course, said study co-author Blaine Greenwald.In any case, the study is preliminary and more research must be done, he said.

Greenwald is from Hillside Hospital, part of Long Island Jewish Medical Center in Glen Oaks, N.Y. He did the work at the Mount Sinai Medical Center in New York with colleagues from there and the Bronx Veterans Administration Hospital.

Alzheimer's disease is a progressive brain disorder that affects an estimated 2.5 million Americans and causes some 150,000 deaths a year. Symptoms include gradual memory loss, impairment of judgment, disorientation, personality change, difficulty in learning and loss of language. No cause or cure is known.

The study focused on 64 Alzheimer's patients whose conditions were assessed at six-month intervals for up to three years. Patients were not treated for depression.

Higher levels of depression in the initial assessment were linked to slower decline on behavioral measures. The measures cover such aspects as delusions and hallucinations, agitation and restlessness and appetite disturbances.

But depression made no difference in the disease's impact on such measures as naming objects, knowing the date, ability to follow commands and memory for words.

Greenwald said some studies suggest that Alzheimer's patients with depression have an underlying abnormality in certain brain cells.