CHICAGO - Chronic dizziness that is not due to vertigo, a problem that has puzzled doctors for years, may have a variety of causes including anxiety disorders and brain injury, according to a study published Monday.

Vertigo, a feeling of turning or whirling usually involving inner ear problems, is well recognized, according to the report from the University of Pennsylvania Health System in Philadelphia.

But so-called chronic nonspecific dizziness where victims also suffer imbalance and are super-sensitive to some motions such as walking in a busy store or driving in the rain is more complex, it added.

The study, published in the February issue of the Archives of Otolaryngology-Head & Neck Surgery, tracked 345 men and women age 15 to 89 who had dizziness for three months or longer due to unknown causes.

"All but six patients were diagnosed as having psychiatric or neurologic conditions, including primary or secondary anxiety disorders, migraine, traumatic brain injury" and abnormalities in the body system which controls involuntary actions, the study said.

"The results of this investigation provide some insight into ... mechanisms that may precipitate and perpetuate chronic dizziness," the study added.

"Two-thirds of patients had medical conditions associated with the onset of dizziness, whereas one-third had anxiety disorders as the initial cause," it said.