[Alon]

Reproducible rib pain is typical of costochondritis--but how do fever and an elevated CRP level fit in? Why is the pain unilateral? Fever, focal bone pain, and elevated CRP lead you to consider osteomyelitis, but you've never heard of rib involvement.

Blood culture and bone scan add up

About the time you're contemplating that possibility, a call comes from the microbiology lab: Blood culture is growing gram-positive, coagulase-positive cocci in clusters. You add vancomycin to cover methicillin-resistant Staphylococcus aureus and order a bone scan.

The scan is positive for abnormal increased uptake of radioactive tracer in the anterior aspect of the left fifth rib. Although the radiologist advises that these findings could indicate infection or neoplasia, the positive blood culture leads you to conclude that the patient's illness must be osteomyelitis of the rib!

Conclusive results of the blood culture reveal methicillin-sensitive S aureus. You switch the antibiotics to oxacillin, and a PICC line is placed.

Rare, in the rib

After four days, your patient is afebrile with minimal pain, a repeat blood culture is negative, and the CRP level has fallen to 1.9 mg/L. The boy is discharged on IV antibiotics, and you plan for follow up with the pediatric infectious disease consultant to determine the appropriate duration of the IV antibiotic therapy.

The patient follows up at the pediatric infectious disease clinic of the tertiary care hospital. After two weeks of IV antibiotics, the CRP level has normalized and his pain has resolved. He is switched to oral cephalexin (Keflex) to complete a six-week course.

Rib osteomyelitis accounts for fewer than 1% of cases of osteomyelitis in children--which alone can make it difficult to diagnose. In a review of 106 cases of bacterial rib osteomyelitis, average time to diagnosis was, remarkably, 16 weeks.

The disease can be diagnosed with a bone scan, as it was in this case; diagnosis is also possible with ultrasonography, a plain film, or CT when a high index of suspicion exists. With any of these imaging modalities, the findings that suggest osteomyelitis may also indicate neoplasia, and biopsy of the lesion may be required for definitive diagnosis. S aureus is the causative agent in most reported cases of rib osteomyelitis, although mycobacterial and fungal infections have also been implicated