DEAR MAYO CLINIC: My husband, who is 70, has been having bouts of dizziness and vertigo on and off for a month. His doctor diagnosed him with benign paroxysmal positional vertigo. What causes this? Is there a cure?

ANSWER: Vertigo is a false sensation of rotating, spinning, tumbling or turning. Benign paroxysmal positional vertigo (BPPV) is the most common cause of vertigo. It develops as a result of an inner ear problem. BPPV can usually be resolved with a treatment that's performed in a doctor's office.

Within your inner ear is the vestibular labyrinth, a sensory system that makes you aware of head rotation and movement. It also detects the pull of gravity. This system is important because it allows you to keep your eyes looking straight ahead and have clear, stable vision as you walk, run, move your head or turn your body.

Within the vestibular labyrinth are structures called otolith organs that monitor the movement of your head and its position. Otolith organs contain tiny calcium carbonate crystals that rest embedded in a membrane attached to nerve cells. If, for example, you tip your head, the crystals sink and stimulate the nerve cells, sending impulses to your brain telling you that that your head is tipped.

In BPPV, the crystals dislodge from the otolith organs and float into another area of the vestibular labyrinth called semicircular canals. These loop-shaped structures contain fluid and hair-like sensors that monitor the rotation of your head. The crystals incorrectly stimulate the semicircular canals when you move your head in certain positions. That stimulation sends signals to your brain that indicate your head is rotating in ways it's really not. Those signals also generate inappropriate eye movements (nystagmus), so you experience both an internal sensation of spinning, and you see the world spinning around you because your eyes are jerking back and forth. BPPV results in vertigo, dizziness and balance problems.

BPPV most commonly occurs when you move your head in a certain direction, lie down from an upright position, turn over in bed or sit up in the morning. Moving your head to look up or look down also can cause BPPV symptoms. Usually, the symptoms last for about a minute and disappear after you stop moving. The condition typically comes and goes over a span of several days or weeks.

What causes the crystals to become dislodged isn't always clear. BPPV occurs most often in people age 60 and older, suggesting that aging may be a factor in BPPV development. BPPV may occur after a blow to the head. Less common causes include disorders that damage the inner ear or, rarely, damage that occurs during ear surgery or during prolonged positioning on your back. In many people, no specific cause for BPPV can be found.

BPPV may go away on its own. In these situations, the crystals may float back to where they're supposed to be, or they may be reabsorbed into vestibular labyrinth fluid. If BPPV doesn't resolve by itself, evaluation and treatment in a doctor's office is the next step. Family physicians, internists, physical therapists, neurologists and otolaryngologists are most likely to be familiar with BPPV and its treatment.

BPPV treatment involves a series of head movements known as the canalith repositioning procedure. The goal is to move the crystals out of the semicircular canals and back into the otolith organs. The canalith repositioning procedure consists of several slow, simple maneuvers for positioning a patient's head. Each position is held for about 30 seconds after BPPV symptoms or abnormal eye movements stop.

After the procedure, the patient must avoid lying flat or placing the treated ear below shoulder level for a day. A person who has had this treatment may need to sleep with his or her head elevated on several pillows the night after the procedure. This allows time for the crystals to settle into the correct area of the vestibular labyrinth and be reabsorbed by the inner ear fluid. The canalith repositioning procedure is usually effective after one or two treatments.

Sometimes patients who continue to have symptoms are instructed how to perform the repositioning procedure on their own. In very rare situations, when the canalith repositioning procedure isn't effective, a surgical procedure may be recommended in which a bone plug is used to block the portion of the inner ear that's causing dizziness.

Scott Eggers, M.D., Neurology, Mayo Clinic, Rochester, Minn.

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