In general, SA and OM+SA are easier to diagnose clinically than OM. The symptoms and signs in SA are clear: the joint is acutely swollen, warm and red, and usually, the child refuses motion. By contrast, OM may commence insidiously, and local pain and other signs of inflammation may develop only after 1–2 weeks, sometimes even longer.
As the clinical diagnosis is not always straightforward, help has to be sought from various laboratory indices. Erythrocyte sedimentation rate (ESR) is the traditional marker, but quantitative determination of the serum C-reactive protein (CRP) level has increasingly gained popularity. The best sensitivity in diagnostics is obtained by combining the information from ESR and CRP. We have used a cutoff limit of <20 mm/h for ESR and <20 mg/l for CRP, and are content. If higher cutoff levels are used, specificity may slightly improve but with the cost of lowered sensitivity.
Plain radiograph is of little use in diagnostics. In OM it takes approximately 10 days to show 'rat bites' and therefore a normal radiograph at presentation by no means excludes the possibility of OM.[1,2,10] Ultrasound shows joint effusion in SA, and may be used to guide a diagnostic or therapeutic joint aspiration, but in OM, the information is meager. Today, resources permitting, magnetic resonance imaging is the best tool in diagnosing OM, because it surpasses even scintigraphy in accuracy. It also provides useful information on SA and OM+SA.
Expert Rev Anti Infect Ther. 2011;9(12):1125-1131. © 2011 Expert Reviews Ltd.