An 8-year-old boy is brought to the clinic for evaluation of a limp. The patient first noticed a mild ache in his upper right thigh 6 days ago. The pain is worse in the evening and improves after sleep. He does not recall an injury but notes that the pain started after returning from a weeklong camping trip. His group went hiking each day of the trip except for 2 days in the middle, during which some campers, including the patient, were experiencing vomiting and diarrhea. He had a similar pain in his left thigh 6 months ago, which resolved after a few days. The patient is otherwise healthy and takes no medications. Temperature is 37.8 C (100 F). He bears little weight on his right leg while walking. There is no gross abnormality or tenderness along the thigh. While supine, the patient holds the right hip slightly flexed, resisting extension and internal rotation. Skin examination is normal. Laboratory evaluation reveals a leukocyte count of 8,000/mm³ and erythrocyte sedimentation rate of 10 mm/h. Ultrasound of the right hip shows a small intracapsular fluid collection. Which of the following is the best pharmacotherapy for this patient?

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11ec25c8_d747_65c3_bc81_8f1f360c9358_MD0003_00 This patient has transient synovitis (TS), a benign condition characterized by inflammation of the tissues surrounding the hip joint. Although the cause is unknown, it most commonly occurs in children age 3-8 after a mild viral illness (eg, gastroenteritis, respiratory infection), as in this case. Typical presentation includes acute hip/thigh pain, limp, and decreased range of motion of the hip joint. Patients tend to hold the affected hip in flexion and external rotation (to maximize the joint space) and resist extension and internal rotation. Children with TS are typically well-appearing and afebrile (or have low-grade fever). White blood cell count and inflammatory markers (eg, erythrocyte sedimentation rate, C-reactive protein) are normal or mildly elevated. Ultrasound may reveal small, unilateral or bilateral hip effusions. Treatment is supportive with nonsteroidal anti-inflammatories (eg, ibuprofen) to relieve the swelling and pain. TS is generally self-limiting with an excellent prognosis; full recovery is expected within 1-4 weeks. However, a small subset of patients (<15%) can develop recurrence, as suggested in this patient's history. (Choice A) Doxycycline treats Lyme arthritis, which can present with recurrent joint (most commonly knee) pain. However, the affected joint is typically swollen, the hip is rarely involved, and erythrocyte sedimentation rate is typically elevated; none of these features are seen here. (Choice C) Methotrexate is often used in the treatment of juvenile idiopathic arthritis, a chronic inflammatory condition that presents with chronic joint pain, swelling, and stiffness (often worse in the morning). Hip involvement is rare, and elevated inflammatory markers would be expected. (Choice D) Metronidazole can treat symptomatic giardiasis (eg, diarrhea, vomiting), which is often seen in campers who drink unfiltered water and can last for weeks. This patient's gastrointestinal symptoms are resolved and therefore do not warrant testing or treatment. (Choice E) Vancomycin may be used to treat septic arthritis, which presents in an ill-appearing patient with acute hip pain, fever, and inability to bear weight. In addition, leukocytosis and elevated inflammatory markers are seen in septic arthritis. Educational objective: Transient synovitis of the hip is a benign, self-limiting condition in children age 3-8 that typically presents with acute hip/thigh pain and limp following a viral illness. Patients are generally well-appearing and afebrile without laboratory evidence of significant infection or inflammation. Treatment is supportive, including nonsteroidal anti-inflammatories (eg, ibuprofen). References: Transient synovitis of the hip: a comprehensive review. (http://www.ncbi.nlm.nih.gov/pubmed/23812087) Distinguishing pediatric Lyme arthritis of the hip from transient synovitis and acute bacterial septic arthritis: a systematic review and meta-analysis. (http://www.ncbi.nlm.nih.gov/pubmed/29581924)

An 8-Year-Old Boy Is Brought to the Clinic for Evaluation