Fungi and mycobacteria usually cause a subacute or chronic mono- or oligoarticular arthritis (27). Candida species are an increasing cause of both native and prosthetic joint septic arthritis. Risk factors for this infection include loss of skin integrity, diabetes, malignancy, intravenous drug use, and immunosuppressive therapy including glucocorticoids (28). Patients are often chronically ill and have exposure to broad-spectrum antimicrobials, hyperalimentation fluid, and/or indwelling central intravenous catheters. Other fungi, including Cryptococcus, Blastomyces, Histoplasma, Coccidioides, and Sporothrix are rare causes of septic arthritis (29,30). Mycobacterium tuberculosis is the most common cause of mycobacterial arthritis worldwide and should be considered in a patient presenting with chronic arthritis with risk factors for tuberculosis, including being foreign-born (31).
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Clinical Features
The clinical manifestations, severity, treatment, and prognosis of septic arthritis are dependent on the identity and virulence of the bacterium, source of joint infection, and underlying host factors. Nongonococcal septic arthritis is monoarticular in 80% to 90% of cases. The knee is usually affected (50% of cases) (27) followed by the hip, wrists, and ankles (2). In adults, the majority of hip infections involve prosthetic or osteosynthetic material (1). Arthritis of the small joints of the foot is most often seen in diabetic patients and is usually secondary to contiguous skin and soft tissue ulcerations or adjacent osteomyelitis.
Gonococcal arthritis may present as febrile monoarticular arthritis, usually of the knees, wrists, and ankles (27), or as one of the manifestations of disseminated gonococcal infection. The latter is characterized by fever, dermatitis, tenosynovitis, and migratory polyarthralgia or polyarthritis (19). Skin lesions are often pustular and occur simultaneously with tenosynovitis, predominately affecting the fingers, hands, wrists, or feet. Concomitant mucosal infection of the urethra or cervix is often present but usually asymptomatic. Urethral and cervical cultures or a nucleic amplification test will frequently yield N. gonorrhoeae (19,32).
Symptoms of acute septic arthritis include pain and loss of joint function. Fever and chills are often present. The acutely infected native joint is usually red, warm, and swollen with an obvious effusion. Range of motion is limited and extremely painful. For deep and axial joint, pain is often the only focal symptom. More subtle symptoms and signs may result in a delay of diagnosis and are particularly seen in patients receiving systemic or intra-articular steroids, and in those with immunocompromised status, advanced comorbidities (including rheumatoid arthritis), and extreme age (33). A thorough physical examination may reveal a distant source of joint infection in up to 50% of patients (27).
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Prosthetic joint infection may present acutely as above, particularly in early stage infection, or more indolently with progressive joint pain, minimal swelling or effusion, and absence of fever (34). In late infection a cutaneous draining sinus tract may be present. Rarely, the involved prosthesis may be visible beneath an ulceration or focus of soft-tissue breakdown.
Diseases that can mimic septic arthritis are crystalinduced arthritis, rheumatoid arthritis, systemic lupus erythematosus, spondyloarthropathy, Still’s disease, rheumatic fever, and Kawasaki syndrome.
Diagnostic Approach
A diagnostic approach to acute native joint arthritis is outlined in Figure 1 on page 32 (35,36). Important aspects include exclusion of other causes of arthritis including trauma, rheumatic diseases, and crystalline arthritis. The most important diagnostic test upon which management hinges is diagnostic arthrocentesis. Fluoroscopic or CT-guided arthrocentesis is indicated for axial and deep joints (e.g., sacroiliac or pubic symphysis) or in the event of a “dry tap” of a peripheral joint. Synovial fluid analysis will often suggest whether an acutely painful joint is due to noninflammatory, sterile inflammatory, or septic causes (Table 2 on page 33). In addition, it will provide fluid for culture and gram stain, a rapid test that can guide early empiric antibiotic therapy. Bacterial, fungal, and mycobacterial cultures should always be performed in order to direct pathogen-specific antimicrobial therapy, which is often given as a prolonged course. Antimicrobial therapy should be delayed until arthrocentesis and other appropriate diagnostic cultures are obtained unless the patient shows signs of sepsis.