When the claws come out: A unique case of leg pain

by Haley Moulton, MD (’24)

A 3 yo girl with no significant past medical history presented with 4 days of worsening left leg pain, fussiness, and refusal to ambulate. The day prior to symptom onset she fell while jumping on the bed, and 2 weeks prior she had a viral URI. 

In the ED she was afebrile and her exam was quite limited due to discomfort and irritability. Initial lab work notable for ESR >130, CRP 33, platelets 467. No leukocytosis. Blood culture drawn with no growth. Plain film XR of bilateral hips, left tibia, fibula, and femur without acute abnormality. She was then admitted to the hospitalist service for further workup. RPP was positive for both adenovirus and rhinovirus.

Upon admission to the hospitalist floor she was febrile to 105F axillary. She met 3 ⁄4 Kocher criteria, and the orthopedics team was paged for evaluation to rule-out septic joint. Her exam was overall reassuring; although fussy throughout her entire exam she allowed full ROM of bilateral hips, and had no appreciable warmth, redness, or tenderness of bilateral hips, knees, or ankles. Hip US obtained which showed no joint effusions.

Sedated MRI of pelvis and lumbar spine was then obtained to rule out osteomyelitis or abscess causing persistent fevers, discomfort, and inability to ambulate. Her MRI demonstrated multifocal osteomyelitis of the pelvis, left sacroiliac joint effusion and enhancing synovitis concerning for septic arthropathy, as well as microabscess of the liver and spleen, consistent with disseminated infection. CT-guided right ischium biopsy demonstrated granulomas. Further history was obtained and it was discovered that her family had 2 litters of kittens at home the month prior. Further workup ultimately revealed she had positive Bartonella serologies and positive Bartonella bone PCR.

Her antibiotic course was also complicated. She initially received ceftriaxone and vancomycin for concern of septic joint. She started on cefazolin after her preliminary imaging findings were concerning for disseminated infection. She then transitioned to empiric rifampin and ciprofloxacin following positive Bartonella serologies, however 2 weeks later required switch to doxycycline and gentamicin as well as course of IV methylprednisolone after repeat imaging demonstrated progression of osteomyelitis and increased size of multifocal abscesses. She completed 5 weeks of doxycycline and gentamicin with clinical improvement; her fever resolved, her gait and MSK exam normalized, and her inflammatory markers improved.

 

This is not your typical case of leg pain, but highlights some important learning points:

  • The differential for leg/hip pain is VERY broad! Your differential should include (but is not limited to) infectious (septic arthritis, osteomyelitis, infections with referred pain to hip such as psoas abscess or appendicitis, lyme), inflammatory (transient synovitis – especially in the setting of recent viral illness), and orthopedic (fracture – important to consider with recent trauma, SCFE, Legg Calve Perthes, apophysitis) etiologies
  • Don’t forget the importance of taking a thorough history – findings from history may suggest specific cause, or help guide workup in an undifferentiated case
  • Septic joint is a can’t miss diagnosis – and the Kocher criteria are validated for the hip. There are 4 criteria: Inability to bear weight, fever >101.3F, ESR>40, WBC>12000. The more criteria you meet, the higher the probability of septic joint. If you have ¾ criteria there is a 93% probability of septic hip!
  • Disseminated bartonella is certainly not the first thing that comes to mind when thinking about why a child is refusing to walk. There will always be zebras – and it’s important to know when to consult colleagues in other specialties for further assistance with workup and management