A 72-year-old woman with diabetes mellitus type 2 and chronic kidney disease (eGFR 35 mL/min) is admitted with a 5-day history of severe ear pain, purulent otorrhea, and fever (39.2°C). Otoscopy reveals granulation tissue in the external auditory canal. Culture of ear discharge grows a gram-negative rod that is oxidase-positive and produces green pigmentation on blood agar. Audiometry shows conductive hearing loss. CT temporal bone shows erosion of the temporal bone. What is the most likely diagnosis?

Explanation

## Clinical Presentation of Malignant External Otitis **Key Point:** Malignant (necrotizing) external otitis (MEO) is a life-threatening, progressive infection of the external auditory canal and temporal bone caused by *Pseudomonas aeruginosa*. Despite the name, it is not malignant in the oncologic sense but rather an aggressive, invasive bacterial osteomyelitis. ## Diagnostic Features in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Patient Risk Factors** | Elderly, diabetic, CKD | Immunocompromised; impaired neutrophil function | | **Presentation** | Severe otalgia, purulent drainage | Hallmark of MEO; pain out of proportion to otoscopy findings | | **Otoscopy** | Granulation tissue in EAC | Pathognomonic; represents granulation and osteomyelitis | | **Microbiology** | Gram-negative rod, oxidase-positive, green pigment | *Pseudomonas aeruginosa* (pyoverdine/pyocyanin pigments) | | **Imaging** | Temporal bone erosion on CT | Osteomyelitis; indicates advanced disease | | **Audiometry** | Conductive hearing loss | Ossicular involvement from osteomyelitis | **High-Yield:** The combination of **diabetes + elderly + severe otalgia + granulation tissue + P. aeruginosa** is virtually diagnostic of MEO. ## Pathophysiology ```mermaid flowchart TD A[Pseudomonas aeruginosa colonization<br/>of external auditory canal]:::outcome --> B[Breaks through epithelial barrier<br/>via cerumen impaction or trauma]:::action B --> C[Invades dermis and periosteum<br/>of temporal bone]:::action C --> D{Host immunity<br/>status?}:::decision D -->|Immunocompromised<br/>diabetes, elderly, CKD| E[Osteomyelitis of temporal bone<br/>and skull base]:::urgent D -->|Immunocompetent| F[Localized infection<br/>limited external otitis]:::outcome E --> G[Granulation tissue formation<br/>Bone erosion]:::outcome E --> H[Cranial nerve involvement<br/>CN VII, IX, X, XII]:::urgent H --> I[Skull base osteomyelitis<br/>Sepsis, meningitis]:::urgent ``` **Clinical Pearl:** Facial nerve paralysis (CN VII involvement) is a late, ominous sign indicating skull base osteomyelitis and carries high mortality if untreated. ## Management Principles 1. **Prolonged IV antipseudomonal therapy:** Fluoroquinolone (ciprofloxacin 750 mg PO BID × 4–6 weeks) or IV antipseudomonal beta-lactam (piperacillin-tazobactam, ceftazidime, or meropenem) for 4–6 weeks 2. **Aggressive ear canal debridement** of granulation tissue 3. **Strict glycemic control** in diabetics 4. **Serial imaging** (MRI preferred) to assess response 5. **Hyperbaric oxygen** may be adjunctive in refractory cases **Warning:** Do NOT assume simple otitis media; the presence of granulation tissue and bone erosion mandates aggressive treatment to prevent skull base osteomyelitis and death.