NEW YORK (Reuters Health) - Having isolated arthritis in one knee could be an early warning sign for lung cancer, Italian researchers suggest.

"Knee monoarthritis as an early manifestation of lung cancer has never been described previously," Dr. Fabrizio Cantini, from the Hospital of Prato, told Reuters Health. He noted that the knee trouble in such cases appears very early, "with the consequent possibility of surgical removal of the cancer."

The researchers reviewed the medical records of everyone with isolated knee arthritis seen at their center over a 6-year period, and report their findings in the Annals of the Rheumatic Diseases.

During the study period, 6654 patients were seen for various rheumatic disorders, including 296 with isolated knee arthritis. In five of these patients (1.7 percent), the arthritis appeared to be the first sign of lung cancer.

These five patients were all middle-aged men and each had a long history of heavy cigarette smoking.

In all five men, the cancer could be completely removed surgically, and the patients were in good condition after an average follow-up period of 41 months.

The arthritis totally disappeared in all cases after lung cancer surgery, confirming that the two were linked.

Based on these observations, Cantini advises doctors to order a chest x-ray "every time you see a heavy smoker who presents (with) mild knee arthritis."

SOURCE: Annals of the Rheumatic Diseases, online September 4, 2007.