NEW SOURCE OF `THUNDERCLAP' HEADACHES DISCOVERED.

Byline: Angela La Voie Medical Tribune News Service

Doctors need to take extra special care in identifying the cause of a rare type of headache known as ``thunderclap'' because the same symptoms may be caused by vastly different conditions, a new study suggests.

A thunderclap headache feels just like it sounds - a sudden headache marked by severe pain that can peak in seconds.

The headache is most often caused by hemorrhage, or bleeding, from one of the brain's blood vessels into the space between the two membranes that surround and protect the brain.

Such hemorrhaging is generally caused by an aneurysm, or bulging blood vessel, which can either burst and cause bleeding or lead to a blood clot.

In a study of 10 women with thunderclap headaches, Dutch researchers from the University of Amsterdam found that the patients' headaches were caused by another serious disorder of the brain's blood vessels generally not associated with thunderclap headache. This disorder has a markedly different treatment.

Last week in the international medical journal the Lancet, the researchers reported that the women had thunderclap headaches caused by cerebral venous sinus thrombosis - a clot blocking the large vein along the top of the brain.

Patients with thrombosis would benefit from treatment with the blood-thinning drug heparin, according to the researchers. This drug, however, would worsen the condition of people whose headache resulted from hemorrhage.

The new report puzzled American doctors.

One source of confusion is a struggle to apply the nonmedical term ``thunderclap'' to a variety of sudden, severe headaches.

``The definition of thunderclap headache is very loose,'' said Dr. Ninan Mathew, director of the Houston Headache Clinic.

``Thunderclap headache is abrupt and very rare,'' he said.

``It can last for a few minutes or half an hour and the most common cause is aneurysm,'' said Mathew, also a clinical professor of restorative neurology and neurobiology at the Baylor College of Medicine in Houston.

He added that while it is known that there are thunderclap headaches caused by thrombosis, such headaches are generally accompanied by other symptoms such as seizures and weakness.

``Thunderclap headache is used to describe a group of sudden headaches,'' said Dr. Joel Saper, director of the Michigan Head Pain and Neurological Institute in Ann Arbor.

He noted that thunderclap headache caused by a brain hemorrhage is often accompanied by nausea, a stiff neck and sensitivity to light.

``The most important message to take away from this study is that when you have a patient with a thunderclap, you need to do an imaging test to identify the underlying cause of the headache,'' said Dr. Merle L. Diamond, associate director of the Diamond Headache Clinic in Chicago.