WASHINGTON (CNN) -- An advisory panel to the U.S. Food and Drug Administration Thursday recommended approval of a blood filtering device to treat some cases of rheumatoid arthritis.

Two conditions attached to the approval called for tighter indication for use of the device -- that is, for people with severe cases only, who have failed all drugs -- and for a post-market study to track the device when used in combination with other drugs and to track long term data.

The device, the Prosorba immunoabsorption column -- made by San Diego, California- based Cyprus Bioscience, Inc. -- was approved by the FDA in 1987 for an unrelated rare bleeding disorder.

A trial conducted at 12 arthritis centers shows the blood-filtering device improved symptoms of rheumatoid arthritis such as swollen and tender joints in half the study subjects.

Arthritis experts say the device will likely benefit patients with severe cases of the disease. Patients in the Prosorba column study had already failed an average of five second-line therapies.

"It very well may be helpful for a small percentage of patients with severe rheumatoid arthritis who are just unresponsive to everything," said Dr. Doyt Conn from the Arthritis Foundation. "That kind of patient is becoming less and less common."

This year the FDA approved two new drug therapies for rheumatoid arthritis. It had been more than a decade since a significant new therapy came on the market to treat the disease.

Rheumatoid arthritis is a chronic and debilitating disease in which the body's immune system attacks its own tissue. The disease affects more than 2.5 million Americans between the ages of 25 and 60.

The FDA usually follows the advisory panel's recommendation to approve drugs or devices. Final approval can be expected within 6 months.