Pop singer and wardrobe malfunction poster girl Janet Jackson has been diagnosed with vestibular migraines, a rare form of headache that her publicist blames for her recently canceled "Rock Witchu" concerts.

Migraines affect nearly 30 million Americans, especially women, who suffer from them by a three to one ratio, according to the National Headache Foundation. Doctors aren't sure exactly how many people are affected by vestibular migraines, but they know these headaches have a unique twist that run-of-the-mill, throbbing migraines don't: a component of vertigo.

To learn more about this unusual form of the disorder, we spoke to Susan Broner, an attending neurologist at Roosevelt Hospital's Headache Institute in New York City.

[An edited transcript of the interview follows.]

What are migraines?
Migraine is typically a one-sided, throbbing headache, moderate to severe in intensity and associated with light sensitivity or sound sensitivity and nausea or vomiting with headache. Some people have dizziness or visual aura that precedes the headache.

What are vestibular migraines?

Vestibular migraine is a variant of migraine in which instead of headache being the most predominant feature, dizziness is. Patients usually say that out of nowhere they got extremely dizzy and don't feel like they're on even ground. Some describe a spinning or rocking sensation. They have light or sound sensitivity and get nauseous or throw up. Episodes can last minutes to hours, and there's a chronic form where people have a constant sense of imbalance. In many instances, people have a history of migraine headaches before vestibular migraine shows up.

What causes vestibular migraines?

We believe they're an inherited disorder. Patients' brains are normal on MRI imaging but in the same way that a migraine is a disorder of function, meaning an abnormal firing of pain pathways, we're still trying to figure out the mechanism behind vestibular migraines.

There seems to be hyperexcitability in the brain stem that's overlapping with the vestibular structures—which allow us to keep our balance—that's causing the dizziness.

How common are vestibular migraines, and who is most affected?
There are 30 million Americans with migraine—it's more common than asthma and diabetes combined. It affects women more than men by three to one. Women often start getting migraines in adolescence as their hormones kick in. Sometimes boys can get migraines in childhood. Their average onset is anywhere from the teens to age 40 for men and women.

It seems like vestibular migraines are not very common. Vestibular migraine seems so far to have a female predominance, but it may be that they're more likely to come to the doctor.

It's also possible that they're more common than we think but are undiagnosed or are misdiagnosed as Meniere's disease—a form of vertigo that occurs in older patients—or as benign positional vertigo, in which patients experience brief episodes of vertigo from seconds to minutes long when they move their heads in a certain way. Positional vertigo episodes are caused by an inner ear disorder that's treatable by manual maneuver of the head.

We're doing studies to get a feel for the consistent symptoms each vestibular migraine patient has and how common it is in the population. There may be an overlap between Meniere's and vestibular migraine. With vestibular migraine, people are exquisitely sensitive to motion, but they seem to be more sensitive to migraine triggers like fluorescent lighting or drinking wine. All the migraine triggers affect these patients; vestibular migraine is a disorder of exclusion—you have to rule out seizures and structural abnormalities—so it's one of the clues.

What is the treatment for vestibular migraines, and how is it different from the treatment for other migraines?

There haven't been controlled studies for the best treatment for vestibular migraines; we typically use migraine agents. For frequent or chronic vestibular migraines, we prescribe daily calcium channel blockers (a type of blood pressure medication), antiepileptic drugs and antidepressant selective serotonin reuptake inhibitors (SSRIs). For acute attacks, they're treated with anti-inflammatory or triptan medications (which narrow blood vessels in the brain), antinausea agents, and certain muscle relaxants can help.