A 9-year-old boy is brought to the office by his parents due to knee pain. His mother states, "He started having occasional left knee pain with mild swelling 2 weeks ago, but the pain and swelling have worsened over the last 5 days." The patient plays basketball but has had no recent trauma. Last week, he had a runny nose and sore throat that resolved on their own. The patient has had no fever, headaches, or chest pain. His mother notes that he has been sleeping "a little more than usual" over the last month. The patient recalls a tick bite 3 months ago during a camping trip in Pennsylvania. He does not remember developing a rash at that time. The patient has congenital hearing loss for which he wears a hearing aid. He takes no daily medications and has no known allergies. Temperature is 36.7 C (98 F) and blood pressure is 100/70 mm Hg. Physical examination shows a well-appearing child with a moderately swollen, warm, and mildly tender left knee. There is no erythema. Minimal pain is elicited with full extension of the knee. The patient is able to stand and bear weight. Sensation is intact. Capillary refill in the bilateral lower extremities is brisk. There is a small bruise on his right knee but no rashes or petechiae. Laboratory results are as follows:
A left knee arthrocentesis is performed, and synovial fluid analysis reveals a white blood cell count of 24,000/mm³ with 85% neutrophils.
Left knee arthrocentesis relieves the patient's swelling, and he is now able to walk almost normally. After 3 days, the patient returns for a follow-up visit. His parents are concerned about his ability to participate in sports. A mild effusion is present on left knee examination. Laboratory results are as follows:
Which of the following is the most accurate description regarding this patient's prognosis?

Question

A 9-year-old boy is brought to the office by his parents due to knee pain.  His mother states, "He started having occasional left knee pain with mild swelling 2 weeks ago, but the pain and swelling have worsened over the last 5 days."  The patient plays basketball but has had no recent trauma.  Last week, he had a runny nose and sore throat that resolved on their own.  The patient has had no fever, headaches, or chest pain.  His mother notes that he has been sleeping "a little more than usual" over the last month.  The patient recalls a tick bite 3 months ago during a camping trip in Pennsylvania.  He does not remember developing a rash at that time.  The patient has congenital hearing loss for which he wears a hearing aid.  He takes no daily medications and has no known allergies.  Temperature is 36.7 C (98 F) and blood pressure is 100/70 mm Hg.  Physical examination shows a well-appearing child with a moderately swollen, warm, and mildly tender left knee.  There is no erythema.  Minimal pain is elicited with full extension of the knee.  The patient is able to stand and bear weight.  Sensation is intact.  Capillary refill in the bilateral lower extremities is brisk.  There is a small bruise on his right knee but no rashes or petechiae.  Laboratory results are as follows:
 A left knee arthrocentesis is performed, and synovial fluid analysis reveals a white blood cell count of 24,000/mm³ with 85% neutrophils.
Left knee arthrocentesis relieves the patient's swelling, and he is now able to walk almost normally.  After 3 days, the patient returns for a follow-up visit.  His parents are concerned about his ability to participate in sports.  A mild effusion is present on left knee examination.  Laboratory results are as follows:
 Which of the following is the most accurate description regarding this patient's prognosis?

Quizplus · Accepted Answer

Explanation: This patient's knee joint effusion, minimal pain, no fever, and recent tick bite raise strong suspicion for Lyme arthritis. Although most cases eventually resolve after years, patients are at risk for persistent or recurrent arthritis with joint damage. Therefore, treatment with a 28-day course of oral doxycycline or amoxicillin is recommended. In the past, doxycycline was not generally used to treat Lyme disease in patients age <8 due to the risk of tooth discoloration, but the American Academy of Pediatrics now recommends ≤21-day course of doxycycline as first-line treatment for late Lyme disease. Doxycycline is preferred due to better penetration into the CNS (eradicates organisms lodged there) and excellent efficacy against coinfecting, tick-transmitted pathogens (eg, Anaplasma phagocytophilum). Patients are also advised to rest and avoid high-impact activities until all symptoms resolve to reduce the risk of additional joint damage (Choice C). More than 90% of patients are cured after oral antibiotic therapy. (Choice B) Septic arthritis requires parenteral antibiotics to prevent rapid-onset joint damage and systemic spread. However, septic arthritis is less likely in this case given the negative Gram stain/culture and lack of significant systemic symptoms and pain. Intravenous antibiotics (eg, ceftriaxone) are used to treat severe complications of Lyme disease (eg, carditis, encephalopathy); most other manifestations are treated with oral antibiotics. (Choice D) Monthly antibiotic therapy with penicillin G benzathine is recommended for patients with acute rheumatic fever, which presents as a migratory polyarthritis after an episode of pharyngitis. (Choice E) Recurrent episodes of arthritis requiring anti-inflammatory treatment occur in patients with juvenile idiopathic arthritis (JIA). Oligoarticular JIA can present with knee pain and swelling, but synovial fluid white blood cell count is usually 2,000-20,000/mm³ with a lower predominance of neutrophils (50%-75%). Although some aggressive forms of JIA are associated with a positive rheumatoid factor, this patient's rheumatoid factor is normal. Educational objective: Lyme arthritis is generally treated with a prolonged course of oral doxycycline or amoxicillin. Doxycycline is typically preferred due to better central nervous system penetration and excellent efficacy against coinfecting, tick-transmitted pathogens. Prognosis is favorable, and most patients recover completely. References: Lyme disease in children. (http://www.ncbi.nlm.nih.gov/pubmed/25999224) Diagnosis and treatment of Lyme arthritis. (http://www.ncbi.nlm.nih.gov/pubmed/25999223)

A 9-Year-Old Boy Is Brought to the Office by His