Isolated knee monoarthritis is a newly recognized paraneoplastic syndrome that may herald resectable non-small-cell lung cancer (NSCLC), according to Italian investigators. Isolated knee monoarthritis is a newly recognized paraneoplastic syndrome that may herald resectable non-small-cell lung cancer (NSCLC), according to Italian investigators reporting in the December issue of the Annals of the Rheumatic Diseases.

"Patients with mild knee arthritis, with scanty non-inflammatory fluid accumulation within the joint, who are also heavy smokers, should undergo chest radiography," Dr. Fabrizio Cantini from the Hospital of Prato told Reuters Health. "Doctors should suspect lung cancer when (seeing) such a patient."

Dr. Cantini and colleagues describe the clinical characteristics of five patients presenting with isolated monoarthritis of the knee as the first manifestation of NSCLC. "Isolated knee monoarthritis was defined as the presence of a tender and swollen joint not associated with other rheumatic features at onset."

These five patients represented 1.7 per cent of all patients presenting with isolated monoarthritis of the knee over a six-year period, and all five were middle-aged men with a history of heavy cigarette smoking.

In all cases, synovial fluid was noninflammatory with negative cytology. The diagnosis of NSCLC was confirmed by chest CT and histological examination of bronchoscopic biopsies, the report indicates.

After surgical resection of the primary cancer, both cancer and knee monoarthritis remitted without relapse in all patients over a median follow-up of 41 months.

"Incidence, clinical importance, and utility of rheumatic paraneoplastic syndromes for early detection of cancer (not only lung cancer) should be better addressed over the future," Dr. Cantini said. "Indeed, other clinical manifestations, including distal extremity swelling with pitting edema of the dorsum of the hand or feet, may herald malignancies in some cases."

His group has already started a multicenter prospective study to evaluate the "exact frequency and to confirm the clinical characteristics of isolated knee arthritis as paraneoplastic arthritis," Dr. Cantini said. "In general terms, we would like to evaluate also the possibility of monoarthritis of the knee and of different joints other than the knee. We expect to recruit at least 1000 patients with monoarthritis over one year in 15 Italian centers. I hope this study will disclose its results over the year 2009.