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Elevations were related to disease progression in patients who had medial knee osteoarthritis, but not gout.
Elevations in serum uric acid levels predicted the progression and worsening of joint space narrowing in patients who had medial knee osteoarthritis-but did not have a diagnosis of gout.
Svetlana Krasnokutsky and fellow researchers at New York University pointed out that osteoarthritis is the most common form of arthritis even if not the most well understood. Although the etiology of osteoarthritis is assumed to be mechanical, some evidence suggests an inflammatory role in its pathogenesis.
Biomarkers for prognosis in osteoarthritis would be of great utility in designing clinical trials and, ultimately, in targeting specific therapies. The authors presented serum uric acid levels as a predictor for progression of joint space narrowing in osteoarthritis in a recent Arthritis & Rheumatology article.
The authors conducted a 24-month prospective, natural history study to look at knee osteoarthritis and inflammatory biomarkers. Ultimately, 88 adults who met the American College of Rheumatology criteria for known osteoarthritis, but not gout, were included in the study.
The primary outcome was whether serum uric acid levels were associated with knee joint space narrowing over the 24-month period. Secondary outcomes included the relationships between baseline serum uric acid levels and Kellgren/Lawrence grade, synovial volume on MRI, and pain scores measured by visual analog scale and the Western Ontario and McMaster Universities Osteoarthritis Index.
Serum uric acid levels did not correlate with Western Ontario and McMaster Universities Osteoarthritis Index pain scores (r=0.12, P=0.28) or visual analog scale pain scores (r=0.08, P=0.48).
Serum uric acid levels did not correlate with baseline osteoarthritis severity based on joint space width (r=-0.15, P=0.15) and Kellgren/Lawrence grade (P=0.15).
Age did not correlate with serum uric acid levels (r=0.14, P=0.19).
Serum uric acid levels did correlate with body mass index (r=0.23, P=0.03).
Serum uric acid levels were not significantly correlated with synovial volume after multivariate adjustments (r=0.13, P=0.56).
Serum uric acid levels were significantly correlated with osteoarthritis progression based on joint space narrowing at 24 months (r=0.40, P<0.01).
Serum uric acid levels were significantly higher in patients who had fast osteoarthritis progression compared with those who had no progression (7.1 gm/dL versus 5.8 mg/dL [P=0.02]) or slow versus fast progression (5.6 mg/dL versus 7.1 mg/dL [P<0.01]).
There was no statistical difference in serum uric acid levels between slow progressors and nonprogressors (p=0.69).
Implications for physicians
• Baseline serum uric acid levels in patients with osteoarthritis but not gout appear to predict future progression of knee joint deterioration.
• These results could point to a causal relationship between elevated serum uric acid, high urate in the joint space, and progression of joint damage.
• A serum elevation of uric acid to 6.8 mg/dL or higher seems to be the cut-off point for predicting osteoarthritis progression.
• 6.8 mg/dL is the saturation point for urate crystallization, which supports the idea that urate crystals may cause synovitis and cartilage damage.
• As an inexpensive, readily available, and minimally invasive test, the serum uric acid level can be used to predict progression of knee osteoarthritis and, with further study, may help monitor treatment efficacy in the future.
The NIH provided financial grants for this work.
Svetlana Krasnokutsky, Charles Oshinsky, Mukundan Attur, et al. “Serum urate levels predict joint space narrowing in non-gout patients with medial knee osteoarthritis.” Arthritis & Rheumatology. Vol. 69, No. 6, June 2017, pp 1213–1220 DOI 10.1002/art.40069