The Alzheimer’s Disease and Related Disorders Association identifies seven stages of Alzheimer’s disease, beginning with a genetic or some other kind of pre-disposition to the disease through to stage seven, which is a loss of speech and muscle control. The continued deterioration of cognitive and neurological ability is indicative of the progressive decline doctors expect to see when diagnosing possible and then probable Alzheimer’s disease.

The length of time Alzheimer’s disease takes to progress from possible to probable, and through the various stages, can vary widely. In some patients, the deterioration can take place over as long as 25 years, and some patients reach stage seven within three years. There is no clear determining factor that can predict the length of time the disease will take to progress. The average amount of time a patient had Alzheimer’s disease is 8 to 10 years.

Doctors use the terms possible and probable when identifying Alzheimer’s disease because there is no one clear test that can make a definite diagnosis. Only after they have ruled out all other possible causes for memory loss and cognitive deterioration do they settle on the diagnosis of Alzheimer’s. The NINDS-ADRDA does identify a further category of definite Alzheimer’s disease, but this is not diagnosed until after death. An autopsy carried out by a histopathologist – a scientist who studies disease patterns in tissue – can verify the evidence of Alzheimer’s disease that can be found on a cellular level. Despite the fact that the diagnosis cannot be confirmed until a patient has passed away, a diagnosis of Alzheimer’s disease by a physician is considered to be 90% accurate.

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