Updated 30 November 2018

Diagnosing Alzheimer’s disease

The doctor will first do a memory test, followed by a physical examination, in order to eliminate other possible causes.

It is most important that a doctor or psychiatrist 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 and then a physical examination in order to eliminate other possible causes of the patient’s mental impairment. Therefore the clinical diagnosis of Alzheimer's disease is a diagnosis by exclusion. Various cognitive tests, as well as interviews with family members may be the next step.

Various tests are used to assist in diagnosing Alzheimer's. These could include:

  • Blood tests
  • Brain scan
  • Neurocognitive testing.

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

  • Computerised axial tomography (CAT) exclude disorders with similar symptoms to Alzheimer's disease. CAT scans may reveal changes that are characteristic of the disease.
  • Magnetic resonance imaging (MRI) is a type of scan that 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) is used by researchers to learn more about the brain. It can provide information about blood flow in the brain, metabolic activity and the way that specific receptors are distributed in the brain. More recently, PET has been used to identify and quantify both neurofibrillary tangles and plaques with mildly radio-active substances that bind to them.
  • Single photon emission computerised tomography (SPECT) is a technology that enables researchers to look for the abnormalities typically found in Alzheimer’s disease.   

Read more:

What are the cause of Alzheimer's disease? 

What are the symptoms of Alzheimer's disease? 

How can Alzheimer's disease be prevented?

(Updated and reviewed by Dr Michael S. Mason, MB ChB, FC Psych (South Africa), Consultant Psychiatrist in private practice, Panorama Psychiatry and Memory Clinic, Cape Town March 2015.)

(Previously reviewed by Dr Frans Hugo, MBChB, M.Med Psychiatry)


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