A 35-year-old man comes to the physician with pain in his right knee and ankle for the last 2 weeks. He also has bilateral eye pain, irritation, and blurry vision. On further questioning, he reports burning urination. Last month, the patient developed diarrhea after eating at a local restaurant. The episode resolved spontaneously. On examination, there is bilateral conjunctival injection. He has tenderness in the lumbosacral area. There is swelling and tenderness of the right knee joint and at the calcaneal tuberosity. Urinalysis is normal. Which of the following patients is most likely to develop reactive arthritis?

Question

A 35-year-old man comes to the physician with pain in his right knee and ankle for the last 2 weeks.  He also has bilateral eye pain, irritation, and blurry vision.  On further questioning, he reports burning urination.  Last month, the patient developed diarrhea after eating at a local restaurant.  The episode resolved spontaneously.  On examination, there is bilateral conjunctival injection.  He has tenderness in the lumbosacral area.  There is swelling and tenderness of the right knee joint and at the calcaneal tuberosity.  Urinalysis is normal. Which of the following patients is most likely to develop reactive arthritis?

Quizplus · Accepted Answer

Explanation: The risk of reactive arthritis (ReA) after Chlamydia infection is about 4%-8% in the general population. However, the risk is approximately 20% in patients who are HLA-B27 positive. The cause of this increased risk is not entirely clear. Defective antigen presentation through class I HLA molecules may play a role. Conversely, only 30%-50% of patients with ReA are HLA-B27 positive, suggesting a complex etiology. (Choice B) HLA-B27 positivity alone is a predisposing factor to the development of ReA. Infection with a pathogen likely to trigger such an inflammatory response is necessary for development of the disease. (Choices C and D) Patients with Chlamydia or Salmonella infection in the absence of HLA-B27 have a lower incidence of ReA than patients who are genetically predisposed. Education objective: The incidence of reactive arthritis after infection with Chlamydia or a predisposing gram-negative rod is higher in individuals who are HLA-B27 positive. References: Novel HLA-B27-restricted epitopes from Chlamydia trachomatis generated upon endogenous processing of bacterial proteins suggest a role of molecular mimicry in reactive arthritis. (http://www.ncbi.nlm.nih.gov/pubmed/23867464) Endogenous processing and presentation of T-cell epitopes from Chlamydia trachomatis with relevance in HLA-B27-associated reactive arthritis. (http://www.ncbi.nlm.nih.gov/pubmed/19443418)

A 35-Year-Old Man Comes to the Physician with Pain in His