A 28-year-old woman comes to the office with acute pain in her left knee joint. She had mild discomfort and pain in her right wrist 4 days ago and left ankle pain 2 days ago. The patient has had no recent respiratory illness, diarrhea, urinary symptoms, or vaginal discharge. Her medical history is unremarkable, and she takes no medications except oral contraceptives. The patient drinks a glass of wine daily, but does not smoke or use intravenous drugs. She is single and sexually active. Her last menstrual period was a week ago. Temperature is 38.5 C (101.3 F), blood pressure is 120/80 mm Hg, pulse is 98/min, and respirations are 15/min. Inspection of the knee shows a moderate effusion and faint erythema. There is warmth and tenderness on palpation. Range of motion is limited by significant pain. No skin lesions are present. Synovial fluid analysis shows a white blood cell count of 50,000/mm³ with a predominance of neutrophils. Which of the following is the most likely cause of this patient's symptoms?

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11ec25c8_d306_8771_bc81_8f6b5376a74a_MD0003_00 This patient has features suggesting septic arthritis, including fever and a neutrophilic inflammatory joint effusion. In a young, sexually active individual, septic arthritis is most often caused by disseminated gonococcal infection (DGI). DGI may present with asymmetric polyarthralgias (often but not always associated with tenosynovitis and skin rash) or an isolated septic monoarthritis or oligoarthritis. As in this patient, migratory polyarthralgias may precede purulent monoarthritis, and overlap syndromes can occur. Although the infection originates in genitourinary, pharyngeal, or rectal mucosa, the primary infection is usually silent. Diagnosis of DGI requires joint aspiration for synovial fluid analysis. The synovial white blood cell count is elevated but highly variable and typically lower than in septic arthritis due to other causes. Diagnosis is confirmed by Gram stain of the synovial fluid, blood cultures, and genital/pharyngeal nucleic acid amplification tests for Neisseria gonorrhoeae. synovial fluid analysis (Choice A) Acute HIV infection can cause arthralgias and fever, but inflammatory monoarthritis would be uncommon. Other typical symptoms include a generalized rash, pharyngitis, lymphadenopathy, and mucocutaneous lesions. (Choice B) Acute rheumatic fever generally follows pharyngitis due to group A Streptococcus. Symptoms include migratory arthritis of the large joints, erythema marginatum, subcutaneous nodules, carditis, and Sydenham chorea. (Choice C) Gout causes inflammatory monoarthritis, often with fever. However, this patient has no significant risk factors for gout (eg, alcoholism, hematologic malignancy), and her migratory joint pain is more consistent with DGI. (Choice E) Infective endocarditis can occasionally cause acute septic arthritis, but diffuse arthralgias and myalgias are more typical. This patient has no risk factors (eg, valvular heart disease, intravenous drug use) or other manifestations (eg, Janeway lesions, Osler nodes) of endocarditis. Janeway lesions Osler nodes (Choice F) Non-gonococcal septic arthritis usually causes single-joint involvement (rather than migratory polyarthralgias) and is less likely than DGI in a young, sexually active patient. Risk factors that would raise suspicion for non-gonococcal arthritis include underlying joint disease (eg, rheumatoid arthritis), immune suppression (eg, diabetes), and intravenous drug use. (Choice G) Reactive arthritis is associated with genitourinary infection with Chlamydia trachomatis and certain gastrointestinal infections. Besides peripheral oligoarthritis, common manifestations include enthesitis, conjunctivitis, urethritis, oral ulcers, and keratoderma blennorrhagicum. keratoderma blennorrhagicum Educational objective: Disseminated gonococcal infection may present with asymmetric polyarthralgias (often with tenosynovitis and rash) or isolated septic arthritis. Neisseria gonorrhoeae is the most common cause of septic arthritis in young, sexually active patients. Diagnosis is confirmed by Gram stain of the synovial fluid, blood cultures, and genital/pharyngeal nucleic acid amplification tests. References: Gonococcal and nongonococcal arthritis. (http://www.ncbi.nlm.nih.gov/pubmed/19480997)

A 28-Year-Old Woman Comes to the Office with Acute Pain