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MALIGNANT (NECROTIZING) OTITIS EXTERNA

A Comprehensive 50-Mark Answer for RGUHS University

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DEFINITION

The term "malignant" was coined by Chandler (1968) — not to imply neoplasia, but to reflect the aggressive, destructive, and potentially fatal course of the disease.

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SYNONYMS

• Necrotizing Otitis Externa
• Skull Base Osteomyelitis (SBO) secondary to MOE
• Invasive Otitis Externa
• Malignant External Otitis

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INCIDENCE & EPIDEMIOLOGY

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PATHOPHYSIOLOGY

🔬 Why Diabetics Are Predominantly Affected

DIABETES MELLITUS
       │
       ├──► Microangiopathy → ↓ Blood supply to EAC skin
       │
       ├──► Impaired neutrophil function (chemotaxis + phagocytosis defect)
       │
       ├──► High glucose → Ideal culture medium for Pseudomonas
       │
       └──► Cerumen pH alteration → ↓ Protective acidic environment of EAC

These factors → Pseudomonas establishes persistent infection

Pathological Progression (Scott-Brown's Otorhinolaryngology, 7th Ed.)

Pseudomonas aeruginosa colonizes EAC skin
              │
              ▼
    Periauricular soft tissue cellulitis
              │
              ▼
    Osseocartilaginous junction invasion
    (via fissures of Santorini — anterior EAC)
              │
              ▼
    Osteomyelitis of tympanic bone → Mastoid
              │
              ▼
    Skull Base involvement (petrous apex, clivus)
              │
       ┌──────┴──────┐
       ▼             ▼
  Stylomastoid    Jugular foramen
  Foramen         involvement
  (VII nerve)     (IX, X, XI)
       │             │
  Facial palsy   Dysphagia/
                 Hoarseness
              │
              ▼
    Bilateral spread → Contralateral CN palsy
              │
              ▼
    Cavernous sinus thrombosis / Meningitis / Death

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BACTERIOLOGY

• Produces exotoxin A, proteases, elastases, phospholipases
• Destroys tissue collagen and elastin
• Forms biofilms → antibiotic resistance
• Exotoxin A inhibits protein synthesis (similar to diphtheria toxin)

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CLINICAL FEATURES

Symptoms (Dhingra's Diseases of ENT, 7th Ed.)

• Severe, unremitting, deep-seated otalgia — disproportionate to clinical findings
• Otorrhea — purulent, foul-smelling
• Feeling of fullness in the ear
• Pruritus

• Trismus — invasion of temporomandibular joint
• Periauricular cellulitis
• Parotid swelling

Jugular Foramen Syndrome (Vernet's Syndrome) = CN IX, X, XI palsy together (Harrison's, p. 4839)

Collet-Sicard Syndrome = CN IX, X, XI, XII involvement

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SIGNS

1. Granulation tissue at the floor of the EAC at the osseocartilaginous junction — PATHOGNOMONIC
2. Oedematous, erythematous EAC
3. Tenderness anterior to tragus, over the mastoid, and TMJ
4. Serosanguinous/purulent discharge
5. Tympanic membrane may be intact early; perforated later
6. No lymphadenopathy (unlike malignancy — differential)

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CHANDLER'S STAGING (1977)

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COVENTRY & MARTIN STAGING (Modified)

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DIFFERENTIAL DIAGNOSIS

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INVESTIGATIONS

1. Laboratory

ESR is the single most useful marker for monitoring treatment response — should normalize before antibiotics are stopped. (Hazarika's Textbook of ENT)

2. Imaging

A. High-Resolution CT (HRCT) of Temporal Bone — Investigation of Choice

• Soft tissue opacification of EAC and middle ear
• Erosion of bony EAC walls
• Mastoid opacification
• Destruction of temporal bone
• Infratemporal fossa involvement
• Skull base erosion

B. Technetium-99m (⁹⁹ᵐTc) Bone Scan

• Highly sensitive (>90%) for early bone involvement
• Positive before CT shows changes
• NOT useful for monitoring treatment response (remains positive for months after cure)

C. Gallium-67 Scan

• Investigation of choice for monitoring treatment response
• Reflects disease activity (inflammatory cells)
• Normalizes with successful treatment
• More specific than Tc scan for MOE

D. MRI

• Superior for soft tissue extent and intracranial complications
• Better than CT for dural, meningeal, and CNS involvement
• T1 with Gadolinium — enhances inflamed tissue
• Shows bone marrow involvement earlier than CT

E. PET Scan (FDG-PET/CT)

• Recent advance — gaining importance as monitoring tool
• More specific than Gallium scan
• Useful in assessing residual disease and guiding duration of therapy

Summary of Imaging Modalities

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DIAGNOSTIC CRITERIA (Cohen & Friedman, 1987)

• Refractory otitis externa
• Severe pain
• Edema/granulation in EAC
• Positive ⁹⁹ᵐTc bone scan
• Pseudomonas aeruginosa on culture
• Failure of topical/oral antibiotics >1 week

• Elderly age
• Diabetes mellitus
• Cranial nerve palsy
• Positive CT findings

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CLINICAL PHOTOGRAPH

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MANAGEMENT

FLOWCHART: Approach to Management of MOE

SUSPECTED MALIGNANT OTITIS EXTERNA
              │
     ┌────────▼────────┐
     │  Confirm Diagnosis│
     │  Culture, HRCT,  │
     │  ESR, Bone Scan  │
     └────────┬─────────┘
              │
     ┌────────▼────────┐
     │  Control Diabetes│
     │  (Strict glycaemic│
     │    control)      │
     └────────┬─────────┘
              │
     ┌────────▼──────────────┐
     │  Intravenous Anti-     │
     │  pseudomonal Antibiotics│
     │  (initial 4-6 weeks)   │
     └────────┬───────────────┘
              │
     ┌────────▼────────────────┐
     │  Local Aural Toilet      │
     │  (débridement, suction)  │
     └────────┬─────────────────┘
              │
              ├──► Improving (ESR falling, symptoms resolving)
              │         │
              │    Switch to Oral Ciprofloxacin
              │    (continue 6-8 weeks total)
              │
              └──► Not Improving / CN Palsy / Bone destruction
                        │
                   Surgical Débridement
                   + Continue IV Antibiotics
                   + Consider Hyperbaric Oxygen

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1. MEDICAL MANAGEMENT

A. Antibiotic Therapy

• Excellent oral bioavailability (comparable to IV)
• Excellent bone penetration
• Anti-pseudomonal activity
• Can be used as step-down from IV
• Stell & Maran's Head and Neck Surgery recommends 6–8 weeks minimum

• Ciprofloxacin + Ceftazidime
• Add Rifampicin for biofilm penetration

• Voriconazole (first-line)
• Liposomal Amphotericin B (alternative)
• Duration: prolonged (months)

B. Local Ear Care

• Gentle aural toilet — remove debris, granulation tissue
• Topical ciprofloxacin/ofloxacin ear drops
• Keep ear dry
• Acidifying agents (acetic acid drops) — prophylaxis only

C. Glycaemic Control

• Strict blood sugar control is mandatory — poor glycaemic control leads to treatment failure
• HbA1c target <7%
• Insulin preferred in acute phase

D. Analgesia

• NSAIDs for mild-moderate pain
• Opioids for severe pain (MOE notoriously painful)

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2. SURGICAL MANAGEMENT

Indications for Surgery

1. Failure to respond to medical treatment
2. Extensive bone destruction on CT
3. Abscess formation
4. Facial nerve palsy (decompression considered)
5. Intracranial complications

Types of Surgical Procedures

Surgery is conservative — goal is débridement, not radical resection. Over-aggressive surgery worsens outcomes. (Cummings Otolaryngology, 7th Ed.)

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3. HYPERBARIC OXYGEN THERAPY (HBO)

• Increases tissue oxygen tension → enhances neutrophil killing
• Promotes neovascularization in ischaemic tissue
• Direct bactericidal effect at high pO₂

• Refractory MOE — failure of conventional therapy
• Recurrent disease
• Intracranial complications
• As adjuvant in all severe cases (some centres)

Stell & Maran's and Hazarika both recommend HBO as valuable adjuvant in advanced MOE.

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COMPLICATIONS

LOCAL:
├── Parotitis
├── TMJ involvement / Trismus
└── Pinna perichondritis

REGIONAL:
├── Mastoiditis
├── Petrositis (Gradenigo's syndrome — VI nerve palsy + petrous apex pain)
├── Parapharyngeal space abscess
└── Infratemporal fossa involvement

INTRACRANIAL:
├── Meningitis
├── Extradural abscess
├── Brain abscess
├── Cavernous sinus thrombosis
├── Lateral sinus thrombosis
└── Subdural empyema

CRANIAL NERVE INVOLVEMENT:
└── CN VII, IX, X, XI, XII (as described above)

OUTCOME:
├── Death (untreated or with CN palsy — up to 80%)
├── Permanent CN deficit
└── Recurrence

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PROGNOSIS AND MONITORING

Indicators of Treatment Response

Duration of Treatment

• Minimum 6 weeks antibiotic therapy
• Continue until 3 consecutive normal Gallium scans (some protocols)
• FDG-PET guided cessation — recent advance

Poor Prognostic Factors

1. Facial nerve palsy at presentation
2. Multiple cranial nerve palsies
3. Intracranial extension
4. Bilateral disease
5. Aspergillus as causative organism
6. Poor glycaemic control
7. Advanced age + significant comorbidities

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RECENT ADVANCES (RGUHS Focus)

1. FDG-PET/CT as Gold Standard for Monitoring

• Superior to Gallium-67 scan in sensitivity and specificity
• Quantitative measurement (SUV — Standardized Uptake Value) guides duration of therapy
• Reduces unnecessary prolonged antibiotic courses
• Recent studies (2020-2024) show PET/CT-guided cessation reduced recurrence

2. Role of Non-Pseudomonas and Fungal MOE

• Increasing recognition of Aspergillus MOE — especially in non-diabetic immunocompromised (post-COVID, hematological malignancies)
• Post-COVID MOE with Aspergillus reported increasingly (2021-2023)
• Requires prolonged voriconazole therapy

3. COVID-19 and MOE

• Multiple case reports post-COVID corticosteroid use leading to MOE
• Mucormycosis-associated MOE also described in post-COVID diabetics

4. Biofilm-targeted Therapy

• P. aeruginosa biofilm is key resistance mechanism
• Rifampicin added for biofilm disruption
• Bacteriophage therapy — experimental, promising results

5. MRSA-associated MOE

• Emerging pathogen in post-surgical and hospital-acquired cases
• Requires Vancomycin or Daptomycin

6. Non-diabetic MOE

• Increasing cases in HIV-positive patients, elderly without diabetes, post-chemotherapy
• Harrison's (p. 4839) acknowledges MOE in AIDS and non-diabetic elderly

7. MRI over CT for Staging

• MRI with diffusion-weighted imaging (DWI) better delineates marrow involvement and intracranial extension

8. Topical Ciprofloxacin-HEPES Formulation

• Enhanced penetration through biofilm
• Under clinical trials

9. Immunotherapy Research

• Granulocyte-Colony Stimulating Factor (G-CSF) — experimental adjuvant to correct neutrophil dysfunction in diabetics

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COMPREHENSIVE MANAGEMENT ALGORITHM

ELDERLY DIABETIC / IMMUNOCOMPROMISED
with severe otalgia + EAC inflammation
              │
              ▼
     CLINICAL ASSESSMENT
    ┌──────────────────────┐
    │ Granulation at EAC   │ ──► If present → STRONGLY SUSPECT MOE
    │ (osseocart. junction)│
    └──────────┬───────────┘
               │
               ▼
    INVESTIGATIONS (PARALLEL)
    ├── Culture EAC swab (Pseudomonas)
    ├── HRCT Temporal Bone
    ├── ESR, CRP, FBS, HbA1c, CBC
    ├── Tc-99m Bone Scan (if CT normal but high suspicion)
    └── Biopsy granulation tissue (exclude malignancy)
               │
               ▼
    CONFIRM DIAGNOSIS (Cohen & Friedman criteria)
               │
               ▼
    MULTIDISCIPLINARY TEAM
    (ENT Surgeon + Endocrinologist + Microbiologist
     + Radiologist + Infectious Disease Specialist)
               │
               ▼
    STAGE (Chandler / Coventry-Martin)
               │
    ┌──────────┴──────────────────┐
    ▼                             ▼
Stage I-II                  Stage III-VI
(No CN palsy,               (CN palsy / Skull base /
 No bone destruction)        Intracranial)
    │                             │
IV Ciprofloxacin             IV Ceftazidime
+ Ceftazidime                + Ciprofloxacin
4-6 weeks                    + Surgical Débridement
    │                        + HBO Therapy
    ▼                             │
Improving?                   Improving?
    │                             │
   YES                     YES          NO
    │                       │            │
Oral Ciprofloxacin      Continue      Extended
750 mg BD × 6-8 wks    4-6 wks more  Débridement
    │                       │        + Culture-guided
    ▼                       ▼          antibiotics
Monitor ESR, CRP,        Monitor      + Consider PET/CT
Gallium scan             Gallium      + HBO extended
    │
  CURE
(Normal Gallium/PET,
 ESR <20, no symptoms)

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SURGICAL ANATOMY RELEVANT TO MOE

Fissures of Santorini

• Congenital dehiscences in the cartilaginous EAC (anterior wall)
• Provide direct pathway for infection spread from EAC to:
  • Parotid gland
  • Temporomandibular joint
  • Infratemporal fossa
• Key anatomical reason for rapid spread in MOE

Relevant Anatomical Spaces

EAC → (via Fissures of Santorini)
           │
    ┌──────┴────────────┐
    ▼                   ▼
Parotid space     Infratemporal fossa
    │                   │
    ▼                   ▼
Parapharyngeal   Pterygoid muscles
    space              │
                       ▼
                  Skull base foramina
                  (Jugular, Stylomastoid,
                   Hypoglossal canals)

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COMPARISON: MOE vs CARCINOMA EAC

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SUMMARY TABLE: TEXTBOOK CONTRIBUTIONS

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POINTS TO REMEMBER FOR VIVA/EXAM (RGUHS)

1. Causative organism — Pseudomonas aeruginosa (>95%)
2. Pathognomonic sign — Granulation tissue at floor of EAC at osseocartilaginous junction
3. First cranial nerve involved — CN VII (Facial nerve) — worst prognostic sign
4. Term coined by — Chandler (1968)
5. Best investigation for diagnosis — HRCT temporal bone
6. Best for early bone detection — Tc-99m bone scan
7. Best for monitoring treatment — Gallium-67 scan (or FDG-PET/CT — recent advance)
8. Antibiotic of choice — Ciprofloxacin (excellent bone penetration + oral bioavailability)
9. Anatomical route of spread — Fissures of Santorini
10. Adjuvant therapy — Hyperbaric Oxygen (HBO)
11. Duration of treatment — Minimum 6 weeks, guided by Gallium/PET normalization
12. ESR role — Best clinical marker to monitor treatment response
13. Chandler Stage IV = CN palsy; Stage V = skull base/intracranial

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REFERENCES

1. Harrison's Principles of Internal Medicine, 21st Edition, p. 4839
2. Cummings Otolaryngology — Head and Neck Surgery, 7th Edition
3. Scott-Brown's Otorhinolaryngology, Head and Neck Surgery, 7th Edition
4. Stell & Maran's Head and Neck Surgery and Oncology, 5th Edition
5. Dhingra PL — Diseases of Ear, Nose and Throat, 7th Edition
6. Hazarika P — Textbook of Ear, Nose and Throat Diseases, 13th Edition
7. Zakir Hussain — ENT (RGUHS prescribed textbook)
8. Bailey and Love's Short Practice of Surgery, 28th Edition, p. 775
9. Chandler JR — "Malignant external otitis" — Laryngoscope, 1968
10. Cohen D, Friedman P — "The diagnostic criteria of malignant external otitis" — J Laryngol Otol, 1987
11. Mahdyoun P et al. — FDG-PET in monitoring MOE — Otol Neurotol, 2013
12. Stern Shavit S et al. — Aspergillus MOE — J Laryngol Otol, 2019
13. Post-COVID Aspergillus MOE case series — Am J Otolaryngol, 2022

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