# Expanding the diagnostic spectrum of malignant otitis externa: a case report of proteus infection in a non-immunosuppressed patient

## TL;DR

A rare case of malignant otitis externa caused by Proteus mirabilis in a non-diabetic, immunocompetent patient is reported, highlighting the importance of considering atypical pathogens.

## Contribution

This is one of the few documented cases of Proteus mirabilis causing MOE in a non-immunosuppressed individual.

## Key findings

- Proteus mirabilis was identified as the causative agent in a non-diabetic, immunocompetent patient with MOE.
- The patient responded to piperacillin/tazobactam therapy followed by oral ciprofloxacin.
- The case underscores the need for microbiological confirmation and tailored antibiotic treatment in atypical MOE cases.

## Abstract

Malignant otitis externa (MOE) is a severe and potentially life-threatening infection of the external auditory canal, most frequently caused by Pseudomonas aeruginosa. Although typically seen in immunocompromised individuals—especially those with diabetes mellitus—up to 45% of cases have been reported in non-diabetic patients, highlighting the importance of recognizing atypical presentations. Rare pathogens, such as Proteus mirabilis, have been identified in only a few documented cases. Early diagnosis and prompt intervention are essential to prevent serious complications, including osteomyelitis and intracranial extension.

This report describes a really uncommon case of malignant otitis externa caused by P. mirabilis in a non-diabetic, immunocompetent patient.

A 53-year-old male with no relevant medical history presented with a four-month history of left-sided otorrhea, otalgia, and preauricular pain. Examination and imaging revealed purulent discharge and bone erosion, suggestive of MOE. Empirical treatment with amoxicillin/clavulanic acid was ineffective. Culture identified Proteus mirabilis, resistant to multiple antibiotics but sensitive to piperacillin/tazobactam, which was administered with supportive care. After 17 days of intravenous therapy, the patient improved and was discharged on oral ciprofloxacin to complete a three-month course. Follow-up confirmed clinical resolution without recurrence.

This case report highlights an exceptionally rare occurrence of MEO caused by P. mirabilis in an immunocompetent, non-diabetic patient. It emphasizes the need to consider uncommon pathogens and atypical clinical profiles in MOE. Early diagnosis, microbiological confirmation, and tailored antimicrobial therapy were critical for favorable outcomes.