While many Americans suffer from headaches, not all of them are classified as migraines.

But migraine headaches, suffered by millions of Americans and debilitating for many, are significantly underdiagnosed by physicians, according to a University of Pittsburgh neurologist.

"A review of a number of studies suggests that far more people actually suffer migraine headaches than popularly thought," said Dr. Robert Kaniecki, assistant professor and director of the Headache Center at the University of Pittsburgh Medical Center. "Many people who are diagnosed as having 'tension' or 'sinus' headaches are, in fact, suffering migraines."

The study's findings are published in Wednesday's issue of the Journal of the American Medical Association.

According to the article, more than 28 million Americans suffer from migraine headaches. Eighteen percent of women and 6 percent of men report having migraines at some point. The cost to the U.S. economy is about $17 billion annually in health care and lost labor costs.

Migraine sufferers often find relief with high doses of nonsteroidal and anti-inflammatory drugs such as aspirin, ibuprofen, naproxen, tolfenamic acid or a combination of acetaminophen, aspirin and caffeine. Also, migraine-specific medications such as those from a family of drugs known as triptans are also frequently used and are considered to be the most effective products on the market.

According to Kaniecki, prescription and nonprescription products are used by 9 percent of the population to treat headaches each week, matching hypertension as the most-treated medical condition.

So if don't diagnose migraines, what are they calling these headaches?

One of the most overdiagnosed forms of headacheis the sinus headache, which Kaniecki says exists only in theory. He said research has shown that the majority of patients diagnosed with sinus headache actually have migraines.

"The United States is the only country in the world to have such a thing as 'sinus headache.' A study done in 2002 showed that of 3,038 people who reported that they had sinus headaches, only eight actually had sinus infections," Kaniecki said.

"Over 50 percent of patients with migraine are undiagnosed, and in this group, 42 percent carry the label of 'sinus headache' and 32 percent the diagnosis of 'tension headache,'" Kaniecki said.

But what's the difference, as long as the pain is going away?

Kaniecki said the overdiagnosis of sinus headaches results in an excessive number of prescriptions written to treat the phantom sinus infection, including mass doses of antibiotics and decongestants. This, he said, may be a major contributor to antibiotic resistance.

A primary reason for the underdiagnosis of migraines is a lack of physician education, he said.

"Only 48 percent of internal medicine and 62 percent of family practice residency graduates report being very prepared to treat patients with headache," Kaniecki said.

He said the tools for assessing headaches are most important so that the physician and patient can work together to determine the best diagnosis and treatment.

"The first step is to find out if there are secondary origins of headache, such as a brain tumor or aneurysm. We then assess the patient for a primary headache subtype such as migraine, tension, or cluster," Kaniecki said.

"Once that step is complete, we assess the frequency of episodes to determine whether the patient has an episodic or chronic form of this headache," he said.

The International Headache Society defines chronic headache as attacks that occur more frequently than 15 days a month for more than six months. More than 4 percent of adults in the United States suffer from chronic headaches that are daily or near-daily.

"Episodic tension-type headache annually affects some 38 percent of U.S. adults, yet rarely requires medical attention, given the typical absence of disability or concerning symptoms," Kaniecki said. The pain is generally mild to moderate, usually felt on both sides of the head, and nonthrobbing, with stress as the most common trigger.

"Migraine symptoms may be quite variable," he said. Although typically seen as a throbbing headache felt on one side of the head and associated with nausea and sensitivities to light and noise, victims may also suffer from neck pain or sinus drainage and congestion.

"If one has a stable pattern of disabling headache occurring as episodes over months to years, it almost always represents migraine," Kaniecki said.