Clinical Review: Acute otitis externa

A clinical review of the aetiology, diagnosis and management of otitis externa. By Ms Jessica Bewick, Mr Edward Lindisfarne and Mr Prodip Das

Grade III of the Brighton Grading Scheme for severity of acute otitis externa includes tympanic membrane obscured by oedematous ear canal (Author images)
Grade III of the Brighton Grading Scheme for severity of acute otitis externa includes tympanic membrane obscured by oedematous ear canal (Author images)

Section 1: Epidemiology and aetiology

Acute otitis externa is inflammation of the external ear canal manifested by a range of causative factors. It is thought to have a prevalence of 0.4% and affects around 10% of the population in their lifetime.1

The majority of patients with otitis externa are seen within general practice, with an approximate 3% referral rate to ENT specialists.2 This article aims to review current treatment of acute otitis externa and present a new grading system to help direct therapy in the primary care setting.

Predisposing factors
Otitis externa is classified by predisposing factors (see box, below), but this does not readily aid the clinician to decide between treatment paradigms. Pathologically, the primary process of otitis externa is thought to arise from a disturbance of the lipid/acid balance of the external ear canal.

Predisposing factors for otitis externa5
Type Factor
Anatomical Narrow external auditory meatus: hereditary or acquired, for example chronic infection, exostoses, iatrogenic.
Obstruction of normal meatus: keratosis obturans, foreign body, hearing aid, hirsute
ear canal.
Dermatological Eczema, seborrhoeic dermatitis.
Allergic Atopy, non-atopic allergy, sensitivity to topical preparations.
Physiological Humidity, immunocompromise.
Trauma Cotton buds, laceration, radiotherapy.
Microbiological Active chronic otitis media, exposure to
P aeruginosa or fungi.

This disturbance subsequently reduces the innate defence of the ear canal to pathogens and a secondary bacterial infection occurs.

Most infections involve multiple organisms, with the majority involving Staphylococcus aureus and/or Pseudomonas aeruginosa. Fungal infections contribute to 9-10% of cases.3,4

Microbiology of otitis externa5
Bacteria    Percentage
Pseudomonas spp   50–65
Other organisms Gram-negative 25–35
Staph aureus   15–30
Streptococci   9–15

Section 2: Making the diagnosis

Otitis externa starts with an inflammatory reaction of the skin lining of the ear canal. This may progress to pus formation, canal wall oedema and spreading cellulitis to the pinna and face.

Signs and symptoms range from ear discomfort, pruritus, otorrhoea and conductive hearing impairment to severe pain, occlusive oedema of the canal and systemic effects.

Patients will often present with a history of an itchy ear followed by discharge and pain.

Examination should include otoscopic examination of the ear canal, which may show debris, canal oedema and varying degrees of occlusion.

It is vital to view the tympanic membrane to assess for perforation, retraction pockets or underlying cholesteatoma; in many patients, due to the initial presence of debris, this is not possible and therefore follow-up must be arranged following resolution of the infection.

Signs of severe disease include cellulitis of the pinna and surrounding skin and lymphadenopathy.

Grading scheme
Patients present with a varying severity of signs and symptoms due to the spectrum of disease. In order to classify disease to allow appropriate management we suggest clinicians follow the Brighton grading scheme.

Grade I is characterised by localised inflammation and some pain but usually no hearing loss. The tympanic membrane can be seen and underlying secondary pathology excluded.

In grade II there is debris in the ear canal but it is not completely occluded. Debris may obstruct the view of the tympanic membrane.

In grade III the ear canal is oedematous, occluded and often completely closed. The tympanic membrane cannot be seen.

Grade IV is characterised by oedema and the tympanic membrane is obscured. There is also perichondritis with pinna cellulitis, and the patient will be systemically unwell (fever, pain, signs of sepsis).

Investigations
Investigations required in most cases of otitis externa are minimal. It is advisable to swab the ear canal before commencing therapy.

For those patients with infrequent episodes (for example, one to two per year) no further action is required.

For patients presenting with recurrent disease and/or only short episodes of convalescence between episodes, screening for diabetes is recommended.


Grade 4 on the Brighton grading scheme - perichrondritis (pinna cellutlitis)

Section 3: Managing the condition

Most infections settle with appropriate treatment without the need for secondary care, although for some patients, ENT review is required.

In determining the latter group, there are two issues: first, the problem in assessing the severity of otitis externa; second, instigating management within the appropriate timescale and referral to secondary care when required.

Antimicrobials
The aim of treatment is the delivery of antimicrobials to the site of infection. Before commencing treatment, the ear canal should be swabbed so that in the event initial therapy fails, the original micro-organism has been isolated.

Basing treatment on the grading system guides clinicians to the appropriate management, summarised in the treatment algorithm.

Therapy for grades I-III is with topical antibiotic drops, pain relief and ear care advice with appropriate ENT referral as required.

Topical ear drops (steroid with/without antibiotics) are associated with a reduction in disease persistence with avoidance of side-effects associated with oral antibiotics. As the pathogen can be pseudomonas, a quinolone (for example, ciprofloxacin) or aminoglycoside (for example, gentamicin) should be the first choice.

Membrane perforation
Aminoglycosides are potentially ototoxic and therefore long-term use is not advisable in patients with tympanic membrane perforation.

However, their use is supported by ENT UK for a one-week period as the oedema of the middle ear protects against this side-effect and the toxins produced by bacteria are thought to be far more ototoxic than the medication itself.

It is understandable that GPs will remain concerned regarding this issue and therefore we offer this advice.

In patients where a tympanic membrane perforation cannot be ruled out, we suggest the use of ciprofloxacin drops 0.3%, two drops, three times a day. Betamethasone 0.1% two drops, three times a day can be added if canal oedema is present.

The former are currently off-licence in the UK, although widely used in other countries6 and recommended in core ENT texts and a local NHS guideline (see guidelines, section 6).

Patients should be taught to apply drops by instilling medication while lying on the opposite side. Tragal massage should then be performed for 30 seconds to help work the drops into the medial canal. All patients should be advised to use water precautions, to refrain from swimming and not to insert anything other than drops into the canal.

Application of topical treatment is frequently a problem if the ear canal is oedematous and the affected skin is inaccessible.

The mainstay of management for these patients referred to the ENT department is the atraumatic microsuction of debris followed by insertion of a sponge wick to allow distribution of topical ear drops to the medial ear canal.

Section 4: Prognosis

While most patients will improve rapidly if the correct treatment is commenced, acute otitis externa may progress, despite treatment, requiring acute ENT referral.

Two groups require specific follow-up:

First, those with recurrent infections who may have an underlying cholesteatoma. These patients must have full visualisation of the tympanic membrane, which may only be possible following aural toilet in an ENT clinic.

Second, those patients with underlying systemic disease that may predispose to persistent symptoms, primarily those with undiagnosed diabetes.

 

In patients presenting with recurrent otitis externa, fasting blood glucose should be performed following resolution of the current infection.

Patients who develop other otological symptoms, such as hearing loss, tinnitus, or vertigo, and/or who are identified as having a chronic tympanic membrane perforation should be referred to ENT for further opinion.

Section: 5 Case study

A 36-year-old woman presented with a painful, 'wet' right ear preceded by a few days of general itching. To ease the itching she had inserted a paper clip to scratch the skin. That morning she had used the shower head to blast the ear canal, providing initial relief although the pain had returned. She was otherwise fit and healthy, although she had noticed her left ear feeling rather dulled in the previous couple of months.

Examination revealed an erythematous canal with a normal tympanic membrane. Her GP gave strict instructions regarding water precautions and ear trauma. She was prescribed a 10-day course of a combined steroid and antibiotic topical therapy.

Review after a week showed improvement and the patient was not seen for a further two months.

Over the next year she developed five further attacks of otitis externa, all in the left ear. On one occasion she was referred to the ENT unit for insertion of a Pope wick and subsequent microsuction. While attacks of acute erythema and otalgia cleared with drops, the ear was constantly wet. Fasting blood glucose levels were within normal limits.

Cholesteatoma
The patient was referred to the ENT outpatient clinic where, following microsuction, a white mass extruding from the attic of the left tympanic membrane was seen (see image below).


Following microsuction a white extruding mass was observed (Author images)

Audiological assessment found a conductive hearing loss in that ear. A CT scan of the left temporal bone revealed a soft tissue mass within the middle ear cavity with possible ossicular chain involvement. The patient went on to have a mastoidectomy with removal of the cholesteatoma.

No reconstruction was required, the cholesteatoma being successfully freed from the ossicular chain. The patient was seen regularly over the next year by ENT with no recurrent symptoms.

Section 6: Evidence base

The main issue surrounding the management of acute otitis externa is the choice between topical and systemic treatment and indications for aminoglycoside/non-aminoglycoside antibiotic drops.

Clinical trials

The main outcome showed a lower rate of persistent infection and subsequent consultation after treatment with topical steroids with/without antibiotics over oral therapy. This is supported by a Cochrane review into chronic suppurative otitis media.7

  • Clinical efficacy of three common treatments in acute otitis externa in primary care: randomised controlled trial. BMJ 2003; 327: 1201-5.

This trial shows that using steroid drops in combination with acetic acid or antibiotics improves outcomes with reduction in duration of symptoms over acetic acid drops alone.

This Cochrane review recommended using ciprofloxacin eye drops in the ear as an effective alternative to aminoglycoside ear drops in patients with perforation of the tympanic membrane and otitis media, which can also be applied to acute otitis externa.

Guidelines

This independently produced guideline by the American Academy of Otolaryngology and Head and Neck Surgery Foundation is an excellent tool.

Key text

  • Carney SA. Otitis externa and otomycosis. In: Gleeson MJ (ed). Scott-Brown's Otorhinolaryngology, Head and Neck Surgery. London, Hodder Arnold, 2008; 3351-7.

An excellent text, frequently updated.

Online

Useful patient advice with diagrams and explanation of causative factors.

Click here to take a test on this article and claim a certificate on MIMS Learning

CPD IMPACT: EARN MORE CREDITS

These further action points may allow you to earn more credits by increasing the time spent and the impact achieved.

  • Make a poster of otitis media classification and treatment for your consultation rooms.
  • Review the presentation of cholesteatoma and discuss this at a clinical meeting.
  • Audit whether your patients with recurrent otitis externa have been checked for underlying conditions such as diabetes.
  • Ms Jessica Bewick, ENT SpR, Mr Edward Lindisfarne, surgical trainee and Mr Prodip Das, ENT consultant, at the Royal Sussex County Hospital, Brighton.

References
1. Osguthorpe JD, Nielsen DR. Am Fam Physician 2006; 74(9): 1510-16.

2. Rowlands S, Devalia H, Smith C et al. Br J Gen Pract 2001; 51: 533-8.

3. Grunstein E, Santos FA, Selesnick SH. Otolaryngology, head and neck surgery. New York, McGraw-Hill Medical, 2008.

4. Bojrab DI, Bruderly T, Abdulrazzak Y. Otolaryngol Clin North Am 1996; 29(5): 761-82.

5. Gleeson MJ (ed). Otolaryngology, head and neck surgery London, Hodder Arnold, 2008.

6. Ghosh S, Panarese A, Parker A et al. BMJ 2000; 321: 126-7.

7. Macfadyen CA, Acuin JM, Gamble C. Cochrane Database Syst Rev 2006; (1): CD005608.

Mr Edward Lindisfarne and Mr Prodip Das recommends

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