HSC Section 8_April 2017

Loh and Loh

Antibiotic Treatment It has become increasingly difficult to isolate causative micro- organisms from the EAC for culture-directed therapy because of the use of otic antibiotics at primary care. Only 63.2% (n = 12) of ear swabs were positive. Increasing antibiotic resistance in P aeruginosa represents another problem. This organism has properties that make it inherently resistant to many drug classes and able to acquire resistance through mutation. 16,17 Taking into consideration all forms of infections caused by P aeruginosa from 33 European countries, the European Antimicrobial Resistance Surveillance System Annual Report for 2006 (http://www.rivm.nl/earss/result/Monitoring_ reports/) reported that 18.0% of isolates were multidrug resis- tant (ie, resistant to 3 or more antibiotics). Specific to P aeru- ginosa in MOE, Berenholz et al 18 raised the concern of ciprofloxacin resistance when they reported that 33.0% of isolates were resistant to ciprofloxacin. This was mirrored in other studies in which the rates of ciprofloxacin resistance have ranged from 31.0% to 37.5%. 18-20 Similarly, 33.3% (n = 3) of P aeruginosa isolates in our series were ciprofloxacin resistant. Levenson et al 21 declared that ciprofloxacin mono- therapy was the treatment of choice in MOE. However, cur- rent resistance rates suggest that monotherapy with ciprofloxacin is imprudent in almost one-third of cases. Antibiotic choices in culture-negative patients therefore rep- resent a therapeutic challenge in view of the high antibiotic resistance rates of P aeruginosa . Our results suggest that the empirical use of combination anti-pseudomonal therapy with intravenous ceftazidime and oral ciprofloxacin in culture- negative cases remains relevant despite increasing antibiotic resistance in P aeruginosa . This is consistent with reports in the literature. 18,22 Rubin et al 23 proposed the use of combina- tion therapy with oral rifampacin and ciprofloxacin in treating drug-resistant P aeruginosa , and they showed that their oral and intravenous regimes were equally efficacious. However, in another study by Korvick et al 24 involving 121 patients with positive blood cultures for P aeruginosa , no significant benefit was demonstrated from the addition of rifampacin to existing anti-pseudomonal therapy, suggesting that further clinical studies on the anti-pseudomonal properties of rifam- pacin are needed. In addition, due to the significant risk of hepatotoxicity and drug interactions related to hepatic cyto- chrome P450 upregulation, rifampacin was not considered for our regime. The role of surgery is limited. Only 3 patients in our series underwent surgery, and the indications for surgery were local debridement and to obtain cultures. The useful- ness of surgery was limited in these cases as intraoperative cultures did not yield additional information over ear swab specimens, and disease persisted despite debridement. Conclusion Definite prognostic factors remain elusive. Our experience has shown that age, severity of diabetes, and duration of symptoms cannot be relied upon to predict prognosis. When radionuclide scans are not readily available, anatomic

Figure 3. Clival erosion in central skull base osteomyelitis.

disease was likely with involvement of 2 or more of the fol- lowing areas: temporomandibular joint, temporal bone, and base of skull. The CT findings of our patients were stratified into major and minor findings based on the studies by Peleg et al 13 and Soudry et al. 4 Contrary to the observations by Peleg et al, 13 no correlation was seen between the presence of major area involvement and poor outcome. This lack of correlation was also noted by Sudhoff et al. 14 Bone erosion can only be seen once demineralization has occurred. Demineralization becomes evident after weeks of inflamma- tion, 3 making early disease hard to detect. Moreover, once demineralization has occurred, the bony changes persist even after inflammation has settled. 6 This loose association between bone demineralization and disease activity could account for the lack of reliability of CT scans in predicting outcome. In cases where medial and intracranial extension of disease had to be visualized, we used MRI to better delineate soft tissue involvement. Direct extension of disease medially from the petrous temporal bone can progress to involve the clivus, a central structure at the anterior-most portion of the basilar occipital bone where it meets the sphenoid bone. We considered patients with clival involvement to have central skull base osteomyelitis ( Figure 3 ). Central skull base osteomyelitis can affect the surrounding soft tissues, compromising the lower cranial nerves and brainstem. 15 Extension of disease through the petroclival synchondrosis can result in intracra- nial involvement with the development of meningitis, abscess, and venous sinus thrombosis. 1 Clival involvement was noted in 5 patients. All these patients had disease that persisted after 6 weeks of antibiotics. In the group without clival involvement, only 14.3% (n = 2) had persistent dis- ease. Clival involvement was also seen in all the mortalities that resulted from intracranial involvement. We suggest that patients with clival erosion should be counseled appropri- ately on prognosis and have more aggressive treatment.

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