Gonococcal Arthritis Workup

Cultures of likely sites of gonococcal infection are the most important tests to perform for the diagnosis of disseminated gonococcal infection (DGI). Synovial fluid cultures are positive for N gonorrhoeae in no more than 50% of cases^[1] and alone are insufficient to make a diagnosis of DGI. In addition to synovial fluid culture, cultures of blood, cervix, rectum, urethra, and pharynx should be taken.^[7] Positive culture results help confirm the diagnosis of DGI and provide antibiotic sensitivities for the particular infecting strain of the organism.

Other laboratory tests that are useful in DGI or gonococcal arthritis include the following:

• Complete blood cell count: Most cases involve mild leukocytosis.
• Erythrocyte sedimentation rate (ESR): This is elevated in most cases.
• Synovial fluid analysis

  • Cell count: The cell count is usually greater than 50,000 WBC/µL (typically >90% polymorphonuclear cells). Synovial fluid with this much inflammation may appear purulent.
  • Analysis for crystals
  • Gram stain: Gram-negative intracellular organisms may be demonstrated, although in less than 25% of synovial fluid aspirates.
  • Culture: Note that synovial fluid should be cultured on prewarmed chocolate agar for highest yield (positive findings in only 50% of patients with gonococcal arthritis and 25%-30% of patients with DGI).
• Culture of mucosal surfaces: 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 (MSM). Mucosal surface cultures should be placed on prewarmed selective plates (ie, Thayer-Martin, modified New York media) and blood agar for identification of other possible organisms.
• Urine culture: Culture is noted to produce a higher yield if the sample is the first-void urine (FVU) from the first 20 mL of the void.
• Rectal culture: The swab is inserted approximately 2.5 cm into the canal (ie, to crypts of Morgagni, which is a frequent focus of infection).
• Blood cultures: Bottled blood culture media containing sodium polyethylene sulfate (SPS) inhibits growth.
• Other sexually transmitted infections: Patients should also be tested for other sexually transmitted infections, including HIV, hepatitis B, chlamydia, and syphilis.

• 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.

• Nucleic acid amplification tests (NAATs): NAATs may be used as an adjunct to culture and can be performed on samples from the cervix, urethra, rectum, urine, pharynx, synovial fluid,^[8] and skin^[9] . These tests can help to confirm a diagnosis of DGI when cultures are negative.^{[8, 9, 10]} However, an important limitation of polymerase chain reaction (PCR) or other NAATs is they do not provide antibiotic sensitivities to guide choice of antibiotic for treatment.

• 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 (see Lab Studies).
• 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, this is rarely necessary in gonococcal arthritis.

Biopsy of skin lesions shows dermal vasculitis with perivascular neutrophils. Neutrophilic infiltration of the epidermis may also be seen in pustular lesions.