Diagnosing the cause of aphasia usually begins with a medical history and a physical examination. Sometimes the cause of aphasia is obvious and may be diagnosed before aphasia is noticed. This may be the case with severe head injury or stroke. However, sometimes a physician may need to conduct diagnostic tests to identify the cause of aphasia. These tests may include:

• Imaging tests. Various imaging tests, such as computed axial tomography (CAT) scans and magnetic resonance imaging (MRI), can be used to diagnose problems with the brain. These tests can help identify common causes of aphasia, such as stroke and damage to the brain from a head injury.

• Electroencephalogram (EEG). During this painless test, small electrodes are attached to the scalp. The electrodes are connected by wires (leads) to an electroencephalograph machine that charts the electrical activity of the brain.
  
  

• Blood tests, including a complete blood count (CBC) and a lipid profile (cholesterol test). Blood tests may be useful in determining whether the patient has a high risk of stroke. High cholesterol, for example, may lead to mini-strokes, which can cause aphasia.
  
  
• Evoked-potential study. The brain's response to sight, hearing and touch are tested and measured to reveal any other neurological damage that may have occurred.