There is no laboratory or x-ray test that will diagnose the most common causes of headache – tension-type, migraine and cluster headache. The diagnosis is based on clinical grounds, that is, your symptoms and neurologic examination. This is why your doctor asks you many different questions about the location, duration and frequency of your headaches as well as what tends to trigger them (hormonal and weather changes are common examples).
If features in the clinical history or physical examination suggest the possibility that something more ominous is causing the headache, then further investigation is indicated. Imaging can help identify a headache that is caused by something secondary, such as another disease process (see Chapter 3 - Headaches Due to Diseases). There are some patients that, despite their physician’s reassurance, will not feel reassured about a diagnosis without further testing. The decision to organize testing for patients is up to the discretion of the physician after thorough consultation with the patient; and, so long as there is no added risk to the patient in undergoing that test.
For nearly 30 years physicians have watched the advances that have been made in imaging of neural tissues like the brain. Early radiographic techniques to image the human brain were not terribly beneficial since the brain is almost entirely composed of soft tissue that is not radio-opaque. Therefore, it remains essentially invisible to ordinary or plain x-ray examination. The advent of more sophisticated testing such as the CAT scan and MRI have helped physicians obtain more detailed anatomic images of the brain which can be used for diagnostic and research purposes.
Several routine diagnostic tests that are available in most centres are outlined below:
Computerized Tomography (CT) Scan
This imaging test allows your doctor to visualize your brain, in two-dimensional slices. Split-second computer processing creates these images as a series of very thin X-ray beams pass through your body. Sometimes you may have a dye (contrast medium) injected into a vein before the test. The clearer images produced with the dye make it easier to distinguish a tumor or other pathology from normal tissue. A CT scan exposes you to more radiation than do conventional X-rays, but in most cases, the benefits of the test outweigh the risks. Patients should alert their physician to any allergies; rarely, patients can react to the intravenous dye.
Magnetic Resonance Imaging (MRI)
With the advancement of MRI imaging, physicians have been able to diagnose many different causes of headache. MRI uses the variation in signals produced by protons in the body when the head is placed in a strong magnetic field. Three-dimensional x-rays of the brain are then produced for assessment by a trained physician. Injection of a dye to enhance the cerebral blood vessels (angiography) may be required to diagnose certain causes of headache (underlying aneurysm).
During the test, you are placed in a small, cylindrical tube that can seem confining to some people. The machine also makes a loud thumping and banging noise. In most cases, you’ll be given earplugs to dampen the noise. If you have a history of claustrophobia, your physician can provide you with a mild sedative to allow you to undergo the investigation in a more comfortable manner.
An EEG is a neurological test that measures the electrical signals within your brain, and records them on a graph. An EEG is used to evaluate the cause of seizures, diagnose comas, and evaluate strokes and sleep disorders. It can also be used to determine the presence and location of brain injuries, abscesses, tumours, bleeding within the brain, and to confirm brain death.
Lumbar Puncture (LP)
This procedure (also called a “spinal tap”) is used to collect and look at the fluid (cerebrospinal fluid, or CSF) surrounding the brain and spinal cord. During a lumbar puncture, a needle is carefully inserted into the spinal canal low in the back (lumbar area). Samples of CSF are collected. The samples are studied for color, blood cell counts, protein, glucose, and other substances. Some of the sample may be put into a special culture cup to see if any infection grows. The pressure of the CSF also is measured during the procedure. This procedure may be done to a headache patient to diagnose conditions such as meningitis or subarachnoid hemorrhage.
Other tests to analyze brain function include PET scanning (Positron Emission Tomography), SPECT scan (Single Photon Emission Computed Tomography) or FMRI (Functional MRI). None of these tests is used to diagnose primary headache disorders such as migraine.
By Dr. Ian Finkelstein, M.Sc., M.D., D.A.A.P.M.
Board Certified, American Academy of Pain Management
Director, Toronto Headache & Pain Clinic
Neurologist with interest in headache