How is Alzheimer's disease diagnosed?

To determine if someone has Alzheimer's disease, a doctor will first do a memory test, followed by a physical examination. This is done in order to eliminate other possible causes.

It is most important that a doctor should diagnose Alzheimer's disease, as many other treatable conditions (such as hypothyroidism, vitamin deficiency, hypoglycaemia, anaemia and depression) have symptoms similar to Alzheimer's disease.

Other causes of Alzheimer's disease-like symptoms include an adverse reaction to prescribed medicine or a harmful combination of medicines.

To check whether a person has Alzheimer's disease, the doctor will first do a memory test, followed by a physical examination, to eliminate other possible causes of the patient's mental impairment. The clinical diagnosis of Alzheimer's disease is therefore a diagnosis by exclusion.

Verbal tests, as well as interviews with family members, may be the next step, although these methods will not yield definitive results.

Other tests used to diagnose possible Alzheimer's disease could include:

• Blood tests
• A brain scan
• An electrocardiogram (ECG, a recording of the electric activity of the heart)
• An electro-encephalogram (EEG, a recording of the electric activity of the brain)

Brain scans can provide valuable information about the brain. These include:

• Computerised axial tomography (CAT) - This is done to exclude disorders with similar symptoms to Alzheimer's disease. CAT scans may reveal changes that are characteristic of Alzheimer's disease.
• Magnetic resonance imaging (MRI) - This type of scan provides more detailed information about physical structure and deeper brain tissue near bone and may add diagnostic information. Functional MRI (fMRI) can provide information on the functioning of the brain, including which areas may be underperforming.
• Positron emission tomography (PET) - This provides information about blood flow in the brain, as well as metabolic activity and the way that specific receptors are distributed in the brain. More recently, it's been used to identify and quantify both neurofibrillary tangles and plaques with mildly radio-active substances that bind to these.
• Single photon emission computerised tomography (SPECT) - This is another instrument available to researchers that helps them to look for the abnormalities typical of Alzheimer's disease.