Otitis externa Flashcards
Definition
Infection of the external auditory canal (EAC)
Aetiology
MC caused by:
- Pseudomonas aeruginosa
- Staphylococcus aureus
10-15% are fungal predominantly:
- Aspergillus
- Candida spp
Epidemiology and Risk Factors
Otitis externa is a common GP presentation, with an incidence >1% per year:
- Diabetes
- Dermatitis : any disruption of the normal skin barrier
- Trauma
- Moisture: swimming, humid environment
Risk factors for necrotising otitis externa
- Head & neck radiotherapy
- Diabetes
- Advancing age
- Immunosuppression
What is the cerumen?
Produced by glands in the EAC is acidic, providing a protective barrier for the thin dermis of the canal
Pathophysiology
Disruption of the cerumen barrier can occur with instrumentation (cotton buds, hearing aids, earplugs) leading to accumulation of moisture and a rise in pH.
This environment is conducive to the proliferation of organisms, invasion and inflammation.
Necrotising otitis externa (NOE)
AKA: malignant otitis externa
Invasive form of otitis externa that can lead to osteomyelitis of the temporal bone, multiple cranial nerve palsies and death.
The tight binding of the skin layer to the periosteum in the deep portions of the EAC accounts for the severe otalgia experienced by these patients.
Signs
Ottohoea
Erythema: EAC, may extend to pinna
Fever
Cranial nerve palsies: NOE
Granulation tissue in EAC: NOE
Symptoms
- Pain: ear, jaw, headache. Severe in NOE (patients may wake at night)
- Discharge
- Pruritus
- Hearing loss: conductive resolve with treatment
- Facial weakness (NOE)
Diagnosis
Not required in uncomplicated cases in primary care.
- Swab: for microbiological analysis when there are persistent or recurrent symptoms, or suspicion of necrotising otitis externa
Blood glucose: poor blood glucose control in a diabetic may exacerbate infection
Investigations for potential NOE
- FBC (leukocytosis), CRP, ESR,
- Biopsy: granulation tissue in the EAC or any polyp = sent for MC+S and histology to exclude malignancy
- Contact CT temporal bones: thickened + enhanced tissue (EAC) + bone erosion in NOE
- Technetium-99m bone scan : increased uptake with bony involvement, highly sensitive for NOE
Gallium-67 citrate scan : detects granulocyte: Assess treatment success, as changes to bone turnover detected by technetium scanning will persist through infection clearance
Treatment AOE
- Analgesia: Para, Ibuprofen, Codiene
- Topical therapy:
= ACETIC ACID (mild)
= Abx +/- topical steroids: - Ciprofloxacin 3%
- Dexamethasone 0.1%
or Clotrimazole 1%
ENT referral - Microsuction - to allow topical Abx to reach affected tissue
- Wick insertion = aids delivery of topical therapy
Treatment NOE
- Admission under ENT : potentially with joint input from medical/infectious diseases team
- Vascular access : for long term therapy (minimum 6 weeks)
- IV antibiotics: ceftazidime/as per local formulary
Complications
- Pinna cellulitis
- Chronic otitis externa: prolonged topical antibiotics are a risk factor for fungal overgrowth
- Myringitis
Necrotising otitis externa:
- Meningitis
-Cranial nerve palsies
- Subdural empyema
- Dural sinus thrombophlebitis (dural sinus occlusive disease)