A 14-year-old Caucasian female presented with a 3-month history of progressively worsening lower back pain. Her back pain quality was sharp, with 9/10 pain at its worst. The pain would sometimes radiate to her hips and down her legs and worsen with prolonged walking or activity. She was an otherwise healthy, competitive volleyball player. She had no fevers but did recall some occasional night sweats. There was no appreciable weight loss, no abdominal pain, no urinary or fecal incontinence. She had no recent diarrhea; in contrast, she reported experiencing more constipation in the weeks preceding her diagnosis. She had no significant past medical history and no known medication allergies. She was a freshman in high school and lived on a farm in southeast Michigan, raising chickens, turkeys, and cattle. Her only travel was to Key West, Florida, 3 months earlier. She had no specific risk factors and no known contacts with possible exposure to tuberculosis.
Her symptoms were initially attributed to a musculoskeletal injury secondary to playing volleyball. Anti-inflammatory treatment with non-steroidal anti-inflammatory drugs (NSAIDs) and physical therapy (PT) only provided moderate relief. Her back pain continued to worsen to the point that she was unable to walk without assistance. X-ray imaging of the spine was obtained by her primary care physician and was interpreted as normal, with no abnormalities of the vertebral bodies or disk spaces identified. A chest X-ray showed no pulmonary infiltrates and no masses concerning tuberculosis or other invasive infection. An orthopedic surgeon obtained a magnetic resonance imaging (MRI; Figure 1) of her spine to screen for possible musculoskeletal injury with nerve involvement. Surprisingly, the imaging demonstrated lesions consistent with pre- and para-vertebral phlegmon with associated osteomyelitis of the L4 vertebra and L4-L5 discitis. Blood work was obtained and showed a normal complete blood cell count but elevated inflammatory markers with erythrocyte sedimentation rate (ESR) of 43 mm (normal < 20) and C-reactive protein (CRP) of 1.7 mg/dL (normal < 0.6). She was subsequently referred to a quaternary care children's hospital for further evaluation.
She was admitted to the pediatric general medicine service for presumed vertebral osteomyelitis, and pediatric orthopedic surgery and pediatric infectious diseases were consulted. Upon admission, she was afebrile, and her physical exam was notable for tenderness to palpation over her lower back about the area of L4. She hyperextended her spine with ambulation and was unable to flex her spine without significant pain. Laboratory studies showed a white blood cell (WBC) count of 11.9 K/mcL with 63% neutrophils, hemoglobin of 10.6 g/dL, and platelet count of 370 K/mcL. A procalcitonin level was obtained at 0.1 ng/mL (normal < 0.25 ng/mL). Her inflammatory markers were repeated with ESR 41 mm/Hr and CRP 1.4 mg/dL. Lactate dehydrogenase (LDH) and uric acid (UA) were within normal limits, reducing the likelihood of malignancy. Blood culture was obtained; note that she had not received antibiotics before her arrival. Given the prolonged duration of symptoms, her osteomyelitis was categorized as subacute to chronic, necessitating a longer course of antibiotic therapy of likely 6-12 weeks. A biopsy was requested to obtain specimens for microbiologic cultures to assist with organism identification and susceptibility testing. A computed tomography (CT)-guided tissue biopsy of the vertebral lesion was performed to obtain culture specimens for aerobic, fungal, and acid-fast bacilli (AFB). She was subsequently started on IV cefazolin for empiric treatment of typical organisms causing vertebral osteomyelitis in healthy children, including methicillin-susceptible Staphylococcal aureus (MSSA) and Streptococcus species. Cefazolin was chosen for empiric MSSA coverage, as our institution, as have many medical centers across the United States, has noted an increased incidence of MSSA as opposed to methicillin-resistant S. aureus (MRSA) in pediatric bone and joint infections. Surprisingly, the tissue biopsy culture resulted in the pure growth of a gram-negative rod, initially identified as Salmonella species, with subsequent identification by the Michigan State Health Department Microbiology Laboratory as Salmonella enterica subsp. enterica serovar Poona (S. Poona).
Given the recovery of Salmonella species and unknown susceptibilities initially, cefazolin was transitioned to ceftriaxone for more reliable empiric coverage. A stool specimen was sent for nucleic acid testing. It was negative for the detection of Salmonella, suggesting she was not an active carrier. However, we cannot exclude the possibility that antibiotic treatment for 2 days before the stool specimen submission may have eradicated the infection. The isolate was susceptible to ampicillin, ceftriaxone, trimethoprim-sulfamethoxazole (TMP-SMX), and ciprofloxacin. All other biopsy and blood cultures remained negative for growth. After 5 days of IV antibiotics as an inpatient, she was clinically stable, afebrile, and had adequate oral intake. Given her clinical course and her known isolate susceptibilities, she was an appropriate candidate for an early transition to oral therapy with a highly bioavailable antibiotic. She was discharged home to continue treatment with oral TMP-SMX.
One week after hospital discharge, she developed a pruritic rash worrisome for possible sulfa allergy, and she was transitioned to ciprofloxacin. Her rash resolved, and she completed a 10-week course of antibiotics in total. She wore a supportive back brace for approximately 2 months. With PT, she underwent a gradual build-up of core strength-building and flexibility exercises. By 3 months after the initiation of antibiotics and PT, she resumed limited physical activity and some volleyball practice participation. At the 3-month clinic visit, her lower back pain was entirely resolved, she had a full range of motion on physical exam, and her ESR and CRP had normalized. By 6 months post-treatment, she had completed all PT sessions, and she had resumed full volleyball activity. As of 12 months post-treatment, she remains asymptomatic with normal inflammatory markers.