August 2002

A 22-month-old girl presents with daily fevers for 10 days up to 104° F. She was initially treated with antibiotics for otitis media, then for pneumonia, which had no significant effect. She had a brief period of vomiting and diarrhea during this period. There were no other complaints.

Her immunizations were up to date and there was no travel. She had contact with a healthy family dog but no other animal contact. Her family history is significant for both parents being sick with vomiting and diarrhea a few days prior to the onset of the patient’s fever. The mother had culture-confirmed Campylobacter enteritis. The father presumably had the same.

Because of the above, the child was empirically treated with gentamicin for possible complicated Campylobacter infection pending cultures of blood, urine and stool. There was brief improvement. However, her fever returned and she began having left hip pain. Her hip radiograph is shown in figure 1. Her hip was aspirated with return of normal synovial fluid. Her CBC revealed a WBC count of 20,000 with a normal differential and a normal erythrocyte sedimentation rate. A pelvic MRI is shown in figures 2-5.

What’s Your Diagnosis?

1. Osteomyelitis of the femoral head
2. Ewing sarcoma
3. Appendicitis
4. Psoas abscess

Answer

The MRI reveals a left psoas muscle abscess and the child was taken to interventional radiology for drainage. The pus grew methicillin-sensitive Staphylococcus aureus. She had her drain for about one week and was treated with nafcillin for an additional two weeks, mostly as an outpatient, with good results (figures 6-10). Please don’t write letters about the nurse not wearing gloves in the figures. It is an obvious mistake, and I often use it to teach about proper infection control precautions.

A psoas abscess will frequently mimic a septic hip, frequently resulting in unnecessary drainage of the hip joint. However, the risk of missing a septic hip is too great to take a chance. On the other hand, the normal hip radiograph and normal ESR probably should have prompted doing the pelvic MRI or CT scan before draining the hip. Hindsight is always 20/20.

Psoas abscesses can occur as a complication of appendicitis, inflammatory bowel disease, bacteremic seeding, etc. Treatment is drainage and antibiotics guided by culture results. If an underlying cause is found, of course it should be treated as well.

The MRI ruled out the other choices. However, any of them could potentially present the same way. Figure 11 shows how a Ewing sarcoma of the sacrum might look, and figure 12 shows the MRI appearance of osteomyelitis of the proximal femur. The history of exposure to Campylobacter in the family was probably coincidental, although it may be possible that the child had it and that it played some role. The patient did show some transient improvement with the gentamicin, but there can be some anti-staph activity with this antimicrobial. However, aminoglycosides don’t work well in the abscess environment, which may explain the transient improvement. In any case, the role of Campylobacter (if any) will remain a mystery.