Intractable Otitis Media Presenting as Falsely Positive for Proteinase 3-ANCA: A Case Report

Abstract

Herein, we report a case of otitis media caused by methicillin-resistant Staphylococcus aureus (MRSA), presenting as falsely positive for proteinase 3 (PR3)-antineutrophil cytoplasmic antibodies (ANCA). A 47-year-old woman was referred to our hospital with a complaint of left otorrhea. An otorrhea culture yielded MRSA, and the patient was treated using tympanoplasty. Postoperative administration of teicoplanin lead to drug-induced neutropenia and was discontinued 4 days after the operation. One month after the operation, the patient's otorrhea recurred, and it was accompanied by hearing impairment. The otorrhea culture yielded MRSA again, while serum was positive for PR3-ANCA (6.8 U/mL). As MRSA was detected in the patient's otorrhea sample, she was treated with linezolid. Her symptoms then improved immediately. Although the PR3-ANCA positivity remained, the patient's otorrhea and hearing impairment had not recurred for 3 years when this report was submitted. Therefore, we conclude that this is a case of false PR3-ANCA positivity.

Figure 1, a, b

(a) Left tympanic membrane (TM) before surgery. The TM is thickened and perforated. Otorrhea is observed. (b) Left TM after insertion of tympanic tube. The TM is still thickened.

Figure 2, a–c

(a) Pure tone audiometry (PTA) before surgery. (b) PTA performed when left otorrhea recurred 1 month after surgery. Hearing impairment is observed in the left ear. (c) PTA after linezolid therapy. Hearing level is improved.

Figure 3, a, b

(a) CT scan before surgery. The tympanic cavity is slightly clouded. (b) CT scan performed when left otorrhea recurred 1 month after surgery. The tympanic membrane is thickened, and the tympanic cavity is slightly clouded. No improvement is observed. A mastoidectomy was performed.