An international team of neurologists has released simplified criteria that it hopes will lead to earlier and more reliable diagnosis of Alzheimer's disease.
Writing in The Lancet Neurology, the reseachers note that as many as one-third of Alzheimer's disease diagnoses are incorrect and that newer criteria allow the disease to be distinguished from other types of dementia while those directly affected are still living. With their new algorithm, the diagnosis of Alzheimer's disease now can rely on "just a couple of clinical-biological criteria for all stages of the disease," says team leader Bruno Dubois, MD, of Inserm/Pierre and Marie Curie University/AP-HP Joint Research Unit 975.
Most of the time, the diagnosis of Alzheimer's disease is based primarily on a suggestive clinical picture, according to the team. The diagnosis subsequently is confirmed or rejected using a biomarker. Regarding the clinical picture, they add, three scenarios exist:
- Typical cases (80 percent to 85 percent of all cases): impairment of episodic long-term memory (known as amnestic syndrome of the hippocampal type and corresponding to difficulty remembering a list a words, even with clues, for example);
- Atypical cases (15 percent to 20 percent of cases): atrophy of the posterior part of the cerebral cortex or logopenic aphasia (impairment of verbal memory where the patient inverts the syllables of a word when repeating it, for example), or frontal brain damage (which results in behavioral problems); and
- Preclinical states: asymptomatic at-risk (those without symptoms but im whom positive biomarkers are discovered during scientific studies), and presymptomatic (with a genetic mutation).
One of the following two biomarkers is required:
- In the cerebrospinal fluid (obtained by lumbar puncture): abnormal levels of brain proteins (reduced beta amyloid protein and increased tau protein), or
- In the brain by positron emission tomography, or PET, neuroimaging: elevated retention of amyloid tracer.
At this point, the new algorithm is important mainly for research purposes, the researchers say; in clinical settings, its use is limited to younger people or those with complex cases, because biomarkers are expensive or invasive to use.