Monitoring Arthritis - Biochemical, Metodological and Clinical Aspects

Abstract: Arthritides are musculoskeletal diseases, which predominantly affect the joints e.g. osteoarthritis (OA) and rheumatoid arthritis (RA). Modern treatment strategies include early detection and careful monitoring of the disease course. Close monitoring is also the basis for individualized treatment. Monitoring should be done using methods reflecting different aspects of the disease to get a broad perspective of the disease course. It is of great importance that the methods used for monitoring arthritis are standardized. In paper I, we studied the natural course of knee OA in a population based cohort of middle-aged individuals with chronic knee pain at inclusion, over a 12 year period with a structural method, radiography, and a clinical method. The main finding was that individuals with chronic knee pain were at high risk for developing radiographic knee OA. In paper II, we studied the presence of low-grade systemic inflammation in individuals with chronic knee pain with and without radiographically verified knee OA by measuring high-sensitivity(hs)CRP. We found that low-grade inflammation is a feature of knee OA especially in individuals developing OA in both tibiofemoral (TF) and patellofemoral (PF) compartments. In paper III the diurnal variation of serum COMP was studied in individuals with clinically verified OA and in patients with RA. We found that serum COMP has a half-life of about 7 hours and it has a significant diurnal variation but serum levels were stable during day-time. The objective of study IV was to monitor serum levels of COMP during a randomised controlled trial of physical exercise vs. standardised rest in individuals with symptomatic and radiographic knee OA. Serum COMP levels increased after one hour of physical exercise and decreased after one hour of rest. No increase was seen after a six-week exercise program. In a supplementary study in paper IV we monitored serum COMP with repeated measurements after the exercise session. Serum COMP levels increased immediately after exercise but 30 minutes after the exercise session the levels did not differ significantly from baseline levels. From these studies I conclude that knee pain is often the first sign of knee OA. Elevated levels of hsCRP in serum, particularly in individuals developing combined PF and TFOA, suggest that low-grade inflammation is a feature of early knee OA. COMP has a short half-life in serum and a significant diurnal variation. Serum COMP levels increase after physical exercise but normalize after about 30 minutes of rest. Samples for measuring serum COMP should be obtained at day-time after resting for at least 30 minutes in a sitting position.