n estimated 40 million Americans experience chronic headaches.   For at least half of these people, the problem is severe and sometimes disabling. It can also be costly: headache sufferers make over 8 million visits a year to doctor's offices. Migraine victims alone lose over 64 million workdays because of headache pain.

Understanding why headaches occur and improving headache treatment are among the research goals of the National Institute of Neurological Disorders and Stroke (NINDS). As the focal point for pain research in the Federal Government, the NINDS also supports and conducts studies to improve the diagnosis of headaches and to find ways to prevent them.

Why Does It Hurt?

What hurts when you have a headache? Several areas of the head can hurt, including a network of nerves which extends over the scalp and certain nerves in the face, mouth, and throat. Also sensitive to pain, because they contain delicate nerve fibres, are the muscles of the head and blood vessels found along the surface and at the base of the brain.

The bones of the skull and tissues of the brain itself, however, never hurt, because they lack pain-sensitive nerve fibres.

The ends of these pain-sensitive nerves, called nociceptors, can be stimulated by stress, muscular tension, dilated blood vessels, and other triggers of headache. Once stimulated, a nociceptor sends a message up the length of the nerve fibre to the nerve cells in the brain, signalling that a part of the body hurts. The message in determined by the location of the nociceptor. A person who suddenly realised "My toe hurts," is responding to nociceptors in the foot that have been stimulated by the stubbing of a toe.

A number of chemicals help transmit pain-related information to the brain. Some of these chemicals are natural painkilling proteins called endorphins, Greek for "the morphine within." One theory suggests that people who suffer from severe headache and other types of chronic pain have lower levels of endorphins than people who are generally pain free.

When Should You See A Physician

Not all headaches require medical attention. Some result from missed meals or occasional muscle tension and are easily remedied. But some types of headache are signals of more serious disorders such as head injury and call for prompt medical care. These include:

¨     Sudden, severe headache 

¨     Headache associated with convulsions 

¨     Headache accompanied by confusion or loss of consciousness 

¨     Headache following a blow on the head 

¨     Headache associated with pain in the eye or ear 

¨     Persistent headache in a person who was previously headache free 

¨     Recurring headache in children 

¨     Headache associated with fever 

¨     Headache which interferes with normal life

A headache sufferer usually seeks help from a family practitioner. If the problem is not relieved by standard treatments, the patient may then be referred to a specialist -- perhaps an internist or neurologist. Additional referrals may be made to psychologists.

Diagnosis: What The Physician Looks For

Diagnosing a headache is like playing Twenty Questions. Experts agree that a detailed question-and-answer session with a patient can often produce enough information for a diagnosis. Many types of headaches have clear-cut symptoms which fall into an easily recognisable pattern.

Patients may be asked: How often do you have headaches? Where is the pain? How long do the headaches last? When did you first develop headaches?

The patient's sleep habits and family and work situations may also be probed.

Most physicians will also obtain a full medical history from the patient, inquiring about past head trauma or surgery and about the use of medications. A blood test may be ordered to screen for thyroid disease, anaemia, or infections which might cause a headache. X rays may be taken to rule out the possibility of a brain tumour or blood clot.

A test called an electroencephalogram (EEG) may be given to measure brain activity. EEG's can indicate a malfunction in the brain, but they cannot usually pinpoint a problem that might be causing a headache.

A physician may suggest that a patient with unusual headaches undergo a computed tomographic (CT) scan. The CT scan produces images of the brain that show variations in the density of different types of tissue. The scan enables the physician to distinguish, for example, between a bleeding blood vessel in the brain and a tumour. The CT scan is an important diagnostic tool in cases of headache associated with brain lesions or other serious disease. Experts generally agree, however, that this sophisticated and expensive technology is not required to diagnose simple or periodic headache.

An eye exam is usually performed to check for weakness in the eye muscle or unequal pupil size. Both of these symptoms are evidence of an aneurysm -- an abnormal ballooning of a blood vessel. A physician who suspects that a headache patient has an aneurysm may also order an angiogram. In this test, a special fluid which can be seen on an X ray is injected into the patient and carried in the bloodstream to the brain to reveal any abnormalities in the blood vessels there.

Thermography, an experimental technique for diagnosing headache, promises to become a useful clinical tool. In thermography, an infrared camera converts skin temperature into a colour picture or thermogram with different degrees of heat appearing as different colours. Skin temperature is affected primarily by blood flow. Research scientists have found that thermograms of headache patients show strikingly different heat patterns from those of people who never or rarely get headaches.

A physician analyses the results of all these diagnostic tests along with a patient's medical history in order to arrive at a diagnosis.

Headaches are diagnosed as:

   * Vascular    * Muscle contraction    * Traction    * Inflammatory

Vascular headaches -- a group that includes the well-known migraine -- are so named because they are thought to involve abnormal function of the brain's blood vessels or vascular system. Muscle contraction headaches appear to involve the tightening or tensing of facial and neck muscles. Traction and inflammatory headaches are symptoms of other disorders, ranging from stroke to sinus infection. Some people have more than one type of headache.