A 24-year-old woman comes to the emergency department due to joint pain. A week ago, the patient had a flu-like illness with fever, malaise, and fleeting joint aches in her wrists, ankles, and knees. Over the past 2 days, the joint pain worsened, and she developed new swelling of the right knee. The patient has no chronic medical problems and has had no similar symptoms in the past. She does not use tobacco, alcohol, or injection drugs. She is sexually active, uses an oral contraceptive for birth control, and her last menstrual period was a week ago. Temperature is 38 C (100.4 F). On examination, there is no scleral icterus, facial rash, or oral ulcers but a few scattered painless vesiculopustular lesions are present on the upper extremities. The right knee is warm, swollen, and tender with decreased range of motion. Both ankles and the left wrist are mildly tender to palpation but not swollen or erythematous. Arthrocentesis of the right knee joint yields 20 mL of cloudy fluid with a leukocyte count of 50,000/mm³ (90% neutrophils). Additional evaluation of the joint fluid is most likely to show which of the following?

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This patient has purulent arthritis of the knee, oligoarticular joint pain, and a few vesiculopustular lesions on the extremities, raising suspicion for disseminated gonococcal infection (DGI). DGI is one of the most common causes of septic arthritis in young, sexually active individuals. It is due to the spread of Neisseria gonorrhoeae from a (usually asymptomatic) genitourinary infection into the systemic circulation. Patients typically present with either purulent arthritis or the triad of polyarthralgia, dermatitis, and tenosynovitis; however, some overlap in these 2 syndromes can occur (as in this patient). Microscopy of blood, urine, or joint fluid samples will often reveal gram-negative intracellular diplococci. (Choice B) Salmonella appears as a gram-negative oxidase-negative rod. Patients with sickle cell disease are at increased risk of septic arthritis due to salmonella. However, salmonella is an uncommon cause of septic arthritis in patients who do not have sickle cell disease. (Choice C) Viridans streptococci, a gram-positive alpha-hemolytic cocci in chains, is a common cause of infective endocarditis and can lead to septic arthritis (due to septic emboli). Patients with infective endocarditis can have flu-like symptoms and skin findings (eg, Osler nodes, Janeway lesions). However, vesiculopustular lesions on the arms are much more characteristic of DGI. (Choice D) Staphylococcus aureus, a catalase-positive gram-positive cocci in clusters, is the most common cause of septic arthritis. However, most cases in young adults are linked to injection drug use. In addition, the presence of vesiculopustular lesions and oligoarticular arthralgias make gonococcal arthritis more likely. (Choices E and F) Gout is caused by monosodium urate crystals that appear as needle-shaped negatively birefringent crystals. Pseudogout is caused by calcium pyrophosphate dihydrate crystals that appear as rhomboid-shaped positively birefringent crystals. Both gout and pseudogout cause inflammatory arthritis (eg, redness, warmth, pain, disability) with elevated leukocyte counts on joint fluid aspiration. However, migrating arthralgias and vesiculopustular lesions would be atypical. Educational objective: Septic arthritis in a young, sexually active adult should raise suspicion for disseminated Neisseria gonorrhoeae infection. Patients may also have the triad of polyarthritis, a vesiculopustular skin rash, and tenosynovitis. N gonorrhoeae is a gram-negative diplococci that is usually identified by microscopy, culture, or nucleic acid amplification.

A 24-Year-Old Woman Comes to the Emergency Department Due to Joint