Chapter 3

#### General Principles

Although over 100 different causes of arthritis exist, there is none more important to the emergency physician than the diagnosis of septic (bacterial) arthritis. If septic arthritis goes undiagnosed or untreated, mortality may result and at the least, rapid destruction of articular tissue is inevitable. Some infections, if untreated, can destroy cartilage in as little as 2 days. Depending on the study, the mortality of septic arthritis is around 11%.1

Evaluation begins with a thorough history. The physician should first determine when the pain started. An acute onset (hours to 1 week) suggests trauma, infection, or crystal-induced arthritis. A history of similar attacks might support a diagnosis of crystal-induced arthritis, although this cannot completely rule out an infectious etiology. Chronic joint pain usually suggests a chronic problem, but the clinician should be careful to note any new features that are unusual to the patient and might signify a concomitant condition (i.e., a septic joint in a patient with rheumatoid arthritis [RA] or gout).

The distribution of affected joints and pattern is determined next. Monoarthritis involves one joint, oligoarthritis involves two to three joints, and polyarthritis occurs in more than three joints.2 Symmetric involvement that is additive and initially involves the small joints is found in RA. Migratory arthritis, especially if it occurs in conjunction with a fever, is consistent with rheumatic fever and/or gonococcal arthritis. Further discussion of the differential diagnoses of monoarthritis and polyarthritis are provided below.

Next, the patient should be questioned about constitutional symptoms (e.g., fever), previous episodes, and trauma. Fever and weight loss are important signs because they signify systemic illness. A history of similar previous episodes suggests crystal-induced or other noninfectious causes. If a patient states that he/she has a fever, the physician should think of septic arthritis. Patients who have a history of trauma should be thought of as possibly having a fracture, which may not be seen on the initial x-ray, particularly in the lower extremity where fractures may be occult. Diarrhea, urethritis, or uveitis suggests a reactive type of arthritis. Obtaining a history of a rash or skin lesion may also provide an important clue to the proper diagnosis.

Stiffness is usually an indication of synovitis, but worsening stiffness after sleep that gradually improves (i.e., gelling) with movement suggests RA.3 If the patient complains of weakness, the clinician must differentiate generalized weakness from a focal deficit. Paresthesias may indicate a compressive neuropathy or radiculopathy. Significant muscle pain suggests the possibility of myositis.

When approaching a patient with joint pain, the emergency physician should first remember that the source of the pain may be articular or periarticular (i.e., bursitis, tendonitis, cellulitis). This can best be determined on examination. Some distinguishing features are listed in Table 3–1. In patients with cellulitis, the involvement is usually not isolated to the joint alone. If it is, however, then ...

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