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Although more than 100 different causes of arthritis exist, none is more important to the emergency physician than the diagnosis of septic (bacterial) arthritis. Mortality from untreated septic arthritis can be as high as 11%.1 The rapid destruction of articular tissue is inevitable and can occur in as little as 2 to 3 days. Most of the following diagnoses in this chapter are not made primarily in the emergency department (ED); instead, patients will come in for symptom control due to acute exacerbations. There are many overlapping themes found here, but most importantly, the emergency physician must be cautious as many of the following types of arthritis can mimic septic arthritis.

Like everything else in medicine, the evaluation begins with a thorough history. The physician should first determine when the pain started and if there have been similar attacks in the past. An acute onset without previous similar presentations suggests trauma or infection. A history of similar attacks may support the diagnosis of crystal-induced arthritis or other noninfectious causes, 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's previous presentations and might signify a concomitant condition (i.e., a septic joint in a patient with gout or rheumatoid arthritis).

The distribution of affected joints will also narrow down the differential. Monoarthritis involves one joint, oligoarthritis involves two to three joints, and polyarthritis occurs in more than three joints.2 For example, symmetric involvement that is additive and initially involves the small joints is indicative of rheumatoid arthritis, whereas an arthritis that has a migratory pattern, especially if it occurs in conjunction with fevers, is more consistent with gonococcal arthritis. Infectious arthritis is typically monoarticular, but in 10% to 20% of cases, more than one joint is affected.3–6 Further discussion of the differential diagnoses of monoarthritis and polyarthritis are provided later in this chapter.

Next, the patients should be questioned about constitutional symptoms (e.g., fever) and trauma. Fever and weight loss are important signs because they signify systemic illness. If a patient states that he/she has had fevers, the physician should think of septic arthritis first and foremost. 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, which is inflammation of the synovial membrane. An important aspect to ascertain is whether the stiffness is exacerbated or alleviated after prolonged rest or exercise. The stiffness associated with rheumatoid arthritis is worse after ...

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