A 45-year-old man comes to the emergency department due to 2 days of left knee swelling and pain. The patient has no significant past medical history apart from an episode of facial palsy 3 months ago. Six months ago, he went on a hiking trip to New Hampshire but has no other travel history. The patient is in a long-standing monogamous relationship with his wife and has had no other sexual partners. Temperature is 37.1 C (98.8 F). Examination shows left knee joint swelling with no surrounding erythema. The remainder of the musculoskeletal examination is unremarkable. There is no heart murmur. Which of the following might have prevented this patient's knee condition?

Question

A 45-year-old man comes to the emergency department due to 2 days of left knee swelling and pain.  The patient has no significant past medical history apart from an episode of facial palsy 3 months ago.  Six months ago, he went on a hiking trip to New Hampshire but has no other travel history.  The patient is in a long-standing monogamous relationship with his wife and has had no other sexual partners.  Temperature is 37.1 C (98.8 F).  Examination shows left knee joint swelling with no surrounding erythema.  The remainder of the musculoskeletal examination is unremarkable.  There is no heart murmur.  Which of the following might have prevented this patient's knee condition?

Quizplus · Accepted Answer

This patient has symptoms consistent with long-standing Lyme disease. Lyme disease is caused by the spirochete Borrelia burgdorferi, which is transmitted by the bite of an Ixodes tick. Lyme disease is endemic in the northeastern United States and northern Europe. Like syphilis, another spirochetal infection, Lyme disease progresses through a predictable series of phases: Lyme disease is easily treated with doxycycline or penicillin-type antibiotics (eg, ceftriaxone). This patient does not appear to have noted ECM, for which he would likely have received doxycycline. However, treatment with ceftriaxone when he developed the facial palsy (a possible manifestation of early disseminated Lyme disease) would have prevented progression to late Lyme disease. (Choice A) Allopurinol competitively inhibits xanthine oxidase, suppressing uric acid synthesis. This drug is used to treat gout and prevent uric acid kidney stones and tumor lysis syndrome. (Choice C) Lamivudine is a nucleoside reverse transcriptase inhibitor used for HIV treatment. (Choice D) A Borrelia burgdorferi vaccine, now discontinued due to low sales, contains a recombinant outer surface protein from these bacteria, not live organisms. (Choice E) Mefloquine is an antimalarial drug used in prevention and treatment of Plasmodium falciparum infections, among others. (Choice F) Metronidazole is effective against anaerobic bacteria (eg, Clostridium difficile, Bacteroides) and parasites (eg, Entamoeba histolytica, Giardia lamblia, Trichomonas vaginalis). Educational objective: Early Lyme disease causes flu-like symptoms and erythema chronicum migrans. The second stage of Lyme disease may involve atrioventricular block and facial palsy. Late Lyme disease can cause chronic asymmetric large joint arthritis and encephalopathy. Lyme disease is easily treated with doxycycline or penicillin-type antibiotics (eg, ceftriaxone).

A 45-Year-Old Man Comes to the Emergency Department Due to 2