Approach Considerations
A complete blood count (CBC) should be obtained; most patients with gonococcal arthritis have mild leukocytosis. The erythrocyte sedimentation rate (ESR) is elevated in most cases.
Cultures of likely sites of gonococcal infection are the most important tests to perform for the diagnosis of disseminated gonococcal infection (DGI) and consequent gonococcal arthritis. Synovial fluid cultures are positive for N gonorrhoeae in no more than 50% of cases [1] and alone are insufficient to establish the diagnosis. Cultures of blood, cervix, rectum, urethra, and pharynx should be obtained. [14] Positive culture results help confirm the diagnosis and provide antibiotic sensitivities for the particular infecting strain of the organism.
Patients should be tested for other sexually transmitted infections, including Chlamydia trachomatis, HIV, syphilis, Mycoplasma genitalium, and herpes simplex virus. If risk factors are present, consider further testing for hepatitis B and C. The CDC recommends that the initial laboratory testing for HIV be an HIV-1/2 antigen/antibody combination immunoassay..
Point-of-care ultrasound in the emergency department can aid in diagnosis by identifying tenosynovitis and excluding arthritis or simple soft-tissue swelling. [15] Plain radiography findings of the affected joint are usually normal. However, they may be indicated to exclude articular damage and to rule out other processes, such as fracture.
Biopsy of skin lesions shows dermal vasculitis with perivascular neutrophils. Neutrophilic infiltration of the epidermis may also be seen in pustular lesions.
Arthrocentesis and Synovial Fluid Analysis
Arthrocentesis is mandatory in cases of suspected septic arthritis. Laboratory tests typically performed on synovial fluid include cell count, crystal analysis, Gram stain, and culture.
The cell count is usually higher than 50,000 WBC/µL (with polymorphonuclear leukocytes [PMNs] typically accounting for more than 90%). Synovial fluid with this much inflammation may appear purulent. Gram-negative intracellular organisms may be demonstrated, albeit in less than 25% of synovial fluid aspirates. Synovial fluid should be cultured on prewarmed chocolate agar for highest yield (findings are positive in only 50% of patients with gonococcal arthritis and 25-30% of those with DGI).
Repeat arthrocentesis should be performed when inflammatory synovial effusions recur in order to remove inflammatory mediators, debris, and purulence. Surgical drainage may be needed in joints refractory to drainage via arthrocentesis; however, it is rarely necessary in patients with gonococcal arthritis.
Tissue, Urine, and Blood Culture
Yield is highest if the culture is obtained from the primary infection site. Findings are positive in more than 80% of cases. When obtained from the primary site of infection, 90% of results are positive in cervical samples, 50-75% in male urethral samples, 20% in pharyngeal samples, and 15% in rectal samples. [1]
The pharynx is an important site of infection in pregnant women and in men who have sex with men. For a rectal culture, the swab is inserted approximately 2.5 cm into the canal (ie, to the crypts of Morgagni, a frequent focus of infection). Mucosal surface cultures should be placed on prewarmed selective plates (ie, Thayer-Martin or modified New York media) and blood agar for identification of other possible organisms.
Urine culture is noted to produce a higher yield if the sample is the first-void urine from the first 20 mL of the void.
Bottled blood culture media containing sodium polyethylene sulfate inhibits growth.
Nucleic Acid Amplification Tests (NAATs)
Nucleic acid amplification tests (NAATs) may be used as an adjunct to cultures and can be performed on samples from the cervix, urethra, rectum, urine, pharynx, synovial fluid, [16] and skin. [17] These tests can help to confirm a diagnosis of DGI when cultures are negative. [16, 17, 18] However, an important limitation of polymerase chain reaction (PCR) and other NAATs is they do not provide antibiotic sensitivities to guide choice of antibiotic for treatment.
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Synovial joint.
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The lesion on this patient's heel was due to the systemic dissemination of the N gonorrhoeae bacteria.
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The foot of this patient is swollen due to gonococcal arthritis.
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This patient presented with cutaneous foot lesions that were diagnosed as a disseminated gonococcal infection.
