A 52-year-old man presents with severe ear pain and purulent drainage from the left ear for 3 weeks. He is a diabetic with poor glycemic control (HbA1c 9.2%). On examination, the external auditory canal is edematous and granulation tissue is visible. There is tenderness over the mastoid process and tragus. Otoscopy reveals purulent discharge obscuring the tympanic membrane. A CT scan of the temporal bone shows erosion of the cortical bone of the mastoid. Blood culture grows Pseudomonas aeruginosa. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Malignant Otitis Externa ### Key Distinguishing Features **Key Point:** Malignant otitis externa (MOE) is a life-threatening, invasive infection of the external auditory canal that spreads to the temporal bone and skull base, primarily affecting elderly and immunocompromised patients. ### Diagnostic Criteria Present in This Case | Feature | This Case | Significance | |---------|-----------|-------------| | Age | 52 years | Typically >60, but diabetes increases risk | | Risk factor | Diabetes (HbA1c 9.2%) | Most common predisposing factor | | Duration | 3 weeks | Prolonged, refractory course | | Organism | *Pseudomonas aeruginosa* | Pathognomonic for MOE | | Bone erosion | Mastoid cortex on CT | Hallmark of invasive disease | | Granulation tissue | EAC | Indicates invasive process | | Mastoid tenderness | Present | Sign of osteomyelitis | ### Pathophysiology of MOE 1. **Infection initiation:** Breaks in the skin of the EAC (trauma, cerumen impaction, water exposure) allow bacterial entry 2. **Invasive spread:** In immunocompromised hosts, *Pseudomonas* invades the temporal bone at the junction of the cartilaginous and bony EAC (foramen of Huschke) 3. **Osteomyelitis:** Spreads to mastoid, petrous apex, and skull base 4. **Cranial nerve involvement:** CN VII (facial nerve) most common; CN IX, X, XI, XII may follow 5. **Mortality:** 15–50% if untreated; high morbidity even with treatment ### Management Algorithm ```mermaid flowchart TD A[Suspected MOE: severe ear pain + risk factors + Pseudomonas]:::outcome --> B[Imaging: CT/MRI temporal bone]:::action B --> C{Bone erosion present?}:::decision C -->|Yes| D[Confirm MOE]:::outcome C -->|No| E[Reconsider diagnosis]:::action D --> F[IV antipseudomonal antibiotics]:::action F --> G[Fluoroquinolone preferred: ciprofloxacin or levofloxacin]:::action G --> H[Duration: 4-6 weeks minimum]:::action H --> I[Monitor: clinical response, imaging, ESR/CRP]:::action I --> J{Improvement?}:::decision J -->|Yes| K[Continue antibiotics]:::action J -->|No| L[Consider surgical debridement]:::urgent ``` **High-Yield:** The combination of **diabetes + severe ear pain + Pseudomonas + bone erosion** is pathognomonic for MOE. Early recognition is critical because mortality increases with delayed diagnosis. **Clinical Pearl:** Ciprofloxacin (500–750 mg IV/PO twice daily) is the drug of choice for MOE because it achieves excellent bone and temporal bone penetration. Treatment duration is typically 4–6 weeks, with some cases requiring 8–12 weeks. ### Why This Is NOT the Other Diagnoses - **Acute otitis externa:** Confined to EAC skin; no bone erosion or systemic signs - **Acute suppurative otitis media:** Affects middle ear, not EAC; no mastoid erosion on CT - **Chronic suppurative otitis media:** Involves middle ear and mastoid, but not EAC granulation tissue or Pseudomonas monoculture [cite:Dhingra 7e Ch 8]