SPECT imaging may lead to early diagnosis of Alzheimer's

Alzheimer's disease (AD) currently afflicts approximately 4.5 million Americans. One of the most feared diseases of old age, AD robs its victims of their memories and personalities long before it takes their lives. Curing or slowing the progress of AD has been a high priority in the scientific community, but an early and accurate diagnosis is equally important given that several other forms of dementia display the same symptoms as AD, especially in the early stages.

A promising breakthrough in differentiating early-stage Alzheimer's disease from other forms of dementia, collectively known as frontotemporal disease (FTD), has been reported by researchers from the University of Texas Southwestern Medical Center (Dallas) in the May edition of The Journal of Nuclear Medicine (JNM). Using single-photon emission computed tomography (SPECT) imaging, researchers found that AD patients exhibited reduced blood flow in the posterior cingulate cortex--an area of the brain that plays a part in orientation, sensory interpretation and vocabulary retention--very early in the course of their disease.

Recognizing this posterior cingulate sign gives doctors the ability to identify the onset of AD in patients significantly sooner than current methods. "We have cases where the first sign of Alzheimer's disease to appear in the patients was the posterior cingulate sign itself, accompanied by only the beginning symptoms of dementia," said Dr. Frederick J. Bonte, director of the Nuclear Medicine Center at UT Southwestern Medical Center and lead author of the brief communication to the JNM.

For this study, SPECT was used to measure blood flow in the posterior cingulate cortex. Three groups were studied: 20 patients diagnosed as probable AD, 20 diagnosed as probable FTD, and 20 normal elderly volunteers. The researchers found that 16 out of the 20 who were clinically diagnosed as having probable AD showed a restricted blood flow in the posterior cingulate cortex . Only one of the patients whose clinical diagnosis was for FTD showed the same kind of blood flow reduction. That patient was later reclassified as probable Alzheimer's based on clinical symptoms.

Of the four probable Alzheimer's patients that did not show reduced blood flow in the posterior cingulate cortex, three were found to have an atypical type of AD, known as tangle-predominant AD. A definitive diagnosis for the fourth has not been determined. (Tangle-predominant AD can only be diagnosed with an autopsy.) "The fact that this test appears to be insensitive to tangle-predominant AD, may prove to be a benefit when using it to determine an optimal therapeutic approach since research suggests that this atypical form of AD is not likely to respond to the drugs now in development which are principally directed at the amyloid pathway," said Dr. Bonte.

Although further research will be needed to confirm these findings and to tease the significance out of the tangle-predominant results, the prospect of a highly accurate test for very early-stage AD, which could offer patients the option of initiating therapy before so much of the self is lost, is good news for those who fear this debilitating and cruel killer.