Pathogens That Cause Malignant Otitis Externa Have Changed Malignant Otitis Externa: Evolving Pathogens and Implications for Diagnosis and Treatment

Background: Malignant otitis externa (MOE) is essentially an osteomyelitis of the temporal bone and surrounding soft tissue that can be life threatening. It is classically caused by Pseudomonas aeruginosa. Objective: To evaluate recent clinical presentations of MOE at the authors' institution. Design: Retrospective review. Participants: Twenty patients (12 men), with a mean age of 65 years at diagnosis, were identified for this study. Methods: All patients diagnosed with MOE between 1995 and 2012 were reviewed. The diagnosis on these cases was based on the Cohen criteria with some modifications. A CT scan showing bony erosion was used instead of a technetium-99 scan. Usually, antibiotics were prescribed although mastoidectomy was also performed in some patients. Results: Data on culture and sensitivity were documented for all patients. Nine patients (45%) had cultures that grew Pseudomonas aeruginosa. All of these cases were sensitive to ciprofloxacin, but 1 was resistant to levofloxacin. Two cultures had methicillin-resistant Staphylococcus aureus (MRSA) in addition to Pseudomonas. Three patients (15%) had cultures positive for only MRSA. One had MRSA and Klebsiella, and another had pan-resistant Acinetobacter. Of the MRSA cases, 1 was resistant to clindamycin. All MRSA cases were thought to be sensitive to vancomycin, Bactrim, or doxycycline. In the 5 remaining cases, there were multiple organisms and many cultures were polymicrobial. These included Enterococcus in 2 patients, methicillin-sensitive S aureus (MSSA) in 1, other varieties of Staphylococcus in 1, Candida in 1, Aspergillus in 1, and others. Three patients had negative cultures. One-third of the patients infected with Pseudomonas had a facial palsy. The facial palsy was never seen in an MRSA-infected patient, but because of the relatively small numbers in this series this difference was not significant. Seventy-five percent of the patients had diabetes including all 9 patients with Pseudomonas. Only 33% of MRSA-infected patients had diabetes. This difference was statistically significant (P =0.04). Seventy-five percent of the patients had documented resolution of symptoms. One died of a central catheter infection while being treated, and the others were lost to follow-up. The mean antibiotic course was 9.2 weeks, but the most frequent duration of treatment was 6 weeks. Three patients had mastoidectomy. Of the Pseudomonas-infected patients, 5 of the 8 who had a documented resolution of symptoms were treated with oral quinolones. The remaining 3 also had IV antibiotics. Conclusions: In this series, only 45% of MOE cases had cultures positive for Pseudomonas. Reviewer's Comments: Over the past 20 years there has been a shift in the primary pathogen causing MOE from Pseudomonas towards MRSA. The reason for this is not clear but may be related to ciprofloxacin being more commonly used. (Reviewer-Benjamin T. Crane, MD).