Microbiology · Year 2 · from Microbiology
Case 1: Pseudomonas Malignant Otitis Externa
Presentation
A 72-year-old man with poorly controlled diabetes mellitus presents with severe right ear pain for 3 weeks that has progressively worsened despite treatment with topical antibiotic drops. He now reports difficulty swallowing and a new right facial droop. Examination reveals purulent discharge from the ear canal, granulation tissue at the junction of the bony and cartilaginous ear canal, and right-sided facial nerve palsy (House-Brackmann grade IV). Temperature is 38.5°C. CT scan of the temporal bone shows soft tissue in the external auditory canal with erosion of the temporal bone extending to the skull base.
Clinical Image
CT scan demonstrating soft tissue density in the external auditory canal with bony erosion at the skull base, characteristic of necrotizing (malignant) otitis externa.
Image Source: Lecture image - Pseudomonas infections
Questions
- What is the diagnosis and the most likely causative organism?
- Why is this patient at particular risk for this infection?
- What is the significance of the cranial nerve palsy?
- What is the appropriate treatment for this condition?
Answers
- Diagnosis and organism: The diagnosis is malignant (necrotizing) otitis externa caused by Pseudomonas aeruginosa. This is not a malignancy but a severe, invasive infection of the external ear canal that extends into the temporal bone and skull base. The characteristic findings include granulation tissue at the bony-cartilaginous junction of the ear canal, progressive bone erosion, and cranial nerve involvement in advanced cases.
- Risk factors: This patient has two major risk factors: elderly age and poorly controlled diabetes mellitus. The combination of microangiopathy affecting the ear canal vasculature and impaired neutrophil function in diabetics creates a favorable environment for Pseudomonas invasion. Additionally, the relatively poor blood supply to the bony ear canal limits antibiotic delivery and immune cell access to the infected tissue.
- Significance of cranial nerve palsy: The facial nerve palsy (cranial nerve VII) indicates extension of infection to the stylomastoid foramen or through the temporal bone. This is a poor prognostic sign indicating advanced disease. Other cranial nerves may become involved as infection spreads along the skull base, including cranial nerves IX, X, XI, and XII. Extension can lead to osteomyelitis of the skull base, meningitis, or brain abscess, all of which significantly increase mortality.
- Treatment: Treatment requires prolonged intravenous anti-pseudomonal antibiotics, typically for 6-8 weeks or longer. First-line agents include antipseudomonal beta-lactams (piperacillin-tazobactam, ceftazidime, cefepime) or carbapenems, often combined with a fluoroquinolone (ciprofloxacin). Surgical debridement of necrotic bone may be necessary. Strict glycemic control is essential. Serial imaging and inflammatory markers (ESR, CRP) help monitor treatment response. Hyperbaric oxygen therapy may be used as adjunctive treatment.