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Many diseases can cause arthritis. Obtaining a history and performing a physical examination are the first steps in allowing the clinician to accurately characterize the arthritis and approach the differential diagnosis in a focused, logical fashion based on the duration of symptoms, the presence or absence of joint inflammation, the number of joints affected, and the pattern of joint involvement (Table 4–1).
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When evaluating a patient with joint symptoms, it is important to determine whether the symptoms are due to an articular process and not to bursitis, tendinitis, or other soft tissue conditions. The physical examination should also establish whether there are objective findings of arthritis, such as swelling, in the symptomatic joints. Arthralgias in the absence of objective arthritis commonly occur in systemic lupus erythematosus (SLE) and acute viral illnesses but have less diagnostic significance than true arthritis.
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Laboratory tests cannot substitute for clinical evaluation and should never be used as a “screen” for disease. Musculoskeletal complaints are common in the general population, but the prevalence of inflammatory rheumatic diseases is relatively low. Hence, the positive predictive value of many rheumatologic tests is low when tests these are ordered indiscriminately. In general, radiographs add little to the evaluation of acute presentations of arthritis (except in cases of suspected trauma) but often are critical for the assessment of chronic arthritis.
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Inflammatory versus Noninflammatory Arthritis
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The distinction between inflammatory arthritis and noninflammatory arthritis is a critical bifurcation point in the differential diagnosis of arthritis. The most reliable means for making this distinction is analysis of the white blood cell (WBC) count in the synovial fluid. The synovial fluid WBC count is >2000/mcL in inflammatory arthritis and is <2000/mcL in noninflammatory arthritis (see Chapter 2). Arthrocentesis should be performed whenever feasible because although clinical features and other laboratory investigations also help distinguish inflammatory and noninflammatory arthritis, no single finding is definitive.
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Patients with an inflammatory arthritis usually complain of pain and stiffness in involved joints; typically these symptoms are worse in the morning or after periods of inactivity (the so-called “gel phenomenon”) and improve with mild to moderate activity. On examination, the larger joints can be warm and, when severely inflamed as in acute gout or septic arthritis, can have erythema of the overlying skin. Laboratory investigations often reveal an elevated erythrocyte sedimentation rate (ESR) and a high C-reactive protein (CRP) level. In contrast, patients with noninflammatory arthritis have pain that worsens with activity and improves with ...