By the time a person goes to the doctor with symptoms of Alzheimer’s disease, his or her brain is substantially damaged. So scientists are avidly hunting for a way to detect the neurological hallmarks of Alzheimer’s early on, in the hopes they can predict – and eventually prevent – the disease.
Results of a new study testing a brain-imaging technique based on positron emission tomography (PET) show that it can reliably distinguish Alzheimer’s patients from healthy people and those with mild cognitive impairment by detecting plaques and tangles, two types of protein clumps that occur in the brains of Alzheimer’s patients. It’s the first method that’s been able to directly image these neurological changes in living patients, and it could eventually be used to diagnose patients and test new drugs.
The technique is based on a compound, known as FDDNP, that can bind to both plaques and tangles. The compound is radioactively labeled, then injected into patients, where it travels to the brain. The PET scan detects an accumulation of the radioactive compound as it binds to plaques and tangles in different parts of the brain.
In the current study, presented this week at the American Academy of Neurology meeting in San Diego, CA, researchers from the University of California, Los Angeles studied 60 subjects: 20 with Alzheimer’s disease, 20 with mild cognitive impairment, a risk factor for Alzheimer’s disease, and 20 normal controls. They found that Alzheimer’s patients had the greatest buildup of FDDNP, implying the greatest number of plaques and tangles, followed by those with mild cognitive impairment.
The levels also correlate with a progression of the disease. When the scientists retested nine of the patients two years after the initial scans, they found that those whose condition had worsened – normal subjects who had developed a mild cognitive impairment or patients with mild cognitive impairment who had been diagnosed with Alzheimer’s – showed a 5 to 11 percent increase in FDDNP levels, compared with a 3 percent increase in those who remained stable. “This suggests the technology may be useful in early diagnosis and in tracking people over time,” says Gary Small, the UCLA scientist who led the research.
The technique is one of several in development for early diagnosis of Alzheimer’s. Currently, the disease is most commonly diagnosed with behavioral tests, rather than using brain imaging. More recently, doctors have begun diagnosing it with a different form of PET imaging – one that measures brain metabolism, which declines in a characteristic pattern in Alzheimer’s patients. Other methods also show promise, notably, testing spinal fluid for certain substances that build up in those in the early stage of disease.