Approach

Diagnosis is usually clinical, with patients presenting with rapid onset of symptoms.[3]

History and physical exam

National guidelines state that a diagnosis of acute otitis externa (AOE) requires the presence of rapid onset (generally within 48 hours) of symptoms within the past 3 weeks, coupled with signs of ear canal inflammation.[1] Symptoms of ear canal inflammation include ear pain (which can be severe), itching, and fullness, with or without decreased hearing or pain in the ear canal and temporomandibular joint intensified by jaw motion. Signs of ear canal inflammation include tenderness over the tragus, pinna, or both.[1] Manipulation of the ear canal is usually painful. The skin of the external auditory canal has variable degrees of diffuse edema, erythema, and swelling. There may be otorrhea or cellulitis of the pinna and adjacent skin. Otoscopy is recommended to examine the state of the tympanic membrane.

How to examine the ear
How to examine the ear

How to perform an examination of the ear.

Sometimes the canal is very swollen, and this obscures the examination of the tympanic membrane. Variable amounts of drainage and debris will be seen on otoscopic ear exam. The tympanic membrane may be erythematous. In certain instances, cervical lymphadenopathy may be present.

[Figure caption and citation for the preceding image starts]: Swollen ear canal, almost completely closed due to acute otitis externaFrom the collection of Dr Richard Buckingham; used with permission [Citation ends].com.bmj.content.model.Caption@1ea0cb00[Figure caption and citation for the preceding image starts]: White purulent debris can be seen at the external auditory meatusBarry V et al. BMJ 2021;372:n714; used with permission [Citation ends].com.bmj.content.model.Caption@1c051a79[Figure caption and citation for the preceding image starts]: The ear canal is narrowed, making it appear more slit-like, with white debris sitting on the canal wallBarry V et al. BMJ 2021;372:n714; used with permission [Citation ends].com.bmj.content.model.Caption@327aa792

Pneumatic otoscopy and/or tympanometry

Pneumatic otoscopy and tympanometry can be performed to aid in the diagnosis.[1] Pneumatic otoscopy will demonstrate normal tympanic membrane movement, which may be absent in patients with associated acute otitis media. Similarly, in patients with AOE, tympanometry will be normal but will show a flat tracing (type B) in patients with associated acute otitis media. Tympanometry may cause discomfort and pain in patients with AOE. 

Culture and microscopy

Ear cultures are obtained mainly from patients who fail to improve with medical therapy. Cultures are usually unnecessary on initial visit or at the time of diagnosis but can be obtained if desired.[3] The most commonly cultured organisms are Pseudomonas and Staphylococcus species.[1] Negative cultures are sometimes obtained in patients who are on antibiotic treatment, whether topical or systemic. Cultures positive for fungal species are found in patients with fungal otitis externa.

Microscopy of exudate/debris from the ear canal may reveal evidence of fungal infection. White filamentous hyphae are seen in fungal otitis externa (otomycosis). The presence of black spores indicates Aspergillus niger as the causative organism.[1][3]

Radiology

Computed tomography (CT) scans of the temporal bone with and without contrast are recommended in patients who have persistent severe ear pain and fullness despite adequate medical therapy with topical and oral antibiotics. This is to rule out necrotizing otitis externa. Clinical features that would suggest a need for a CT scan include pain that is disproportionate to the clinical findings and patients with granulation tissue along the floor of the external auditory canal, especially in patients with diabetes or those who are immunocompromised.[1] The presence of cranial neuropathies also mandates radiologic evaluation. In similar situations, and if the CT scan shows bony destruction, a magnetic resonance image (MRI) of the internal auditory canals and skull base is obtained to better delineate the extent of infection. Patients with diabetes mellitus and other immunocompromised conditions are particularly susceptible to necrotizing otitis externa and require radiological evaluation if there is any suspicion that they may have the condition.

Re-evaluation in patients refractory to treatment

Patients who fail to respond to conventional treatment of AOE should be re-evaluated to rule out fungal otitis externa, necrotizing otitis externa, or, simply, noncompliance with treatment. Cultures and microscopy can be obtained and may reveal filamentous hyphae and/or spores indicative of fungal infection. Necrotizing otitis externa should be investigated in patients who fail to respond to medical treatment and who have persistent ear pain despite maximal therapy. Radiologic evaluation with CT or MR is indicated.

Necrotizing otitis externa

Necrotizing otitis externa (also called malignant otitis externa) is a form of otitis externa that is more common in older patients with uncontrolled diabetes or in patients with immunodeficiency.[1][4]​ In necrotizing otitis externa, the infection and the inflammatory process involve not only the skin and soft tissue of the external auditory canal but also the bone tissue of the temporal bone.[5] Early symptoms and signs are the same as AOE, but, if left untreated, osteomyelitis of the petrous part of the temporal bone and/or skull base could result, which may invade soft tissue, the middle ear, inner ear, or brain.[1][5][6]​ The facial nerve may be affected, and less frequently, the glossopharyngeal and spinal accessory nerves.[1]

Necrotizing otitis externa is a medical emergency.[7]​ 

Pseudomonas aeruginosa is implicated in most patients.[1][7]​​ Patients usually present with severe ear pain, otorrhea, and fullness, and are not responding to the conventional treatment of AOE. Depending on the stage of presentation and the extent of invasion, patients may have facial weakness and other cranial nerve abnormalities.[1] On physical exam, the external auditory canal is swollen, with evidence of granulation tissue on the floor of the canal and at the bony-cartilaginous junction.[1]

The diagnosis is usually made by computed tomography or magnetic resonance imaging scans, which show presence of soft tissue and bone destruction.[5] Technetium-99 or gallium scans will show increased radioisotope uptake in the temporal bone and/or skull base, although these studies are not routinely indicated for people with suspected necrotizing otitis externa.[20]​ Positron emission tomography-CT will also document increased signal in the skull base.[21]​ The patient’s erythrocyte sedimentation rate (ESR) may also be raised in necrotizing otitis externa.[1][12]​​​

One study recruited 74 UK-based clinicians and used the Delphi method to reach consensus definitions and statements for necrotizing otitis externa.[22]​ The following key consensus definitions and statements have been proposed.

  • Definite necrotizing otitis externa is said to be present when all of the following exist: otalgia plus otorrhea or otalgia plus a history of otorrhea, granulation or inflammation of the external auditory canal, histologic exclusion of malignancy in cases where this is suspected, and radiologic features consistent with necrotizing otitis externa (CT and MRI findings).

  • Possible necrotizing otitis externa: severe infection of the external ear canal without the presence of bony erosion of the external auditory canal on CT scan or absence of changes consistent with necrotizing otitis externa on the MRI scan and that has all of the following characteristics:

    • Otalgia and otorrhea or otalgia and a history of otorrhea

    • Granulation or inflammation of the external auditory canal

    • Any of the following features: immunodeficiency, night pain, raised inflammatory markers (erythrocyte sedimentation rate/C-reactive protein) in absence of other plausible cause, or failure to respond to >2 weeks of topical anti-infectives and aural care.

  • "Necrotizing otitis externa” is the preferred terminology over “malignant otitis externa”.

  • A case of suspected necrotizing otitis externa should be primarily evaluated with a CT scan.

  • Upon confirmed diagnosis of necrotizing otitis externa, specialist review should be arranged.

Fungal otitis externa

Otomycosis is a fungal infection of the external ear canal caused by molds and yeasts.[8]​ Fungal otitis externa accounts for approximately 9% of total otitis externa.[8]​ It presents in a similar way to acute bacterial otitis externa, with ear pain, itching, aural fullness, and otorrhea. It is common in tropical countries, humid locations, after long-term topical antibiotic therapy, and in people with diabetes, HIV/AIDS, or other immunocompromised states.[1] The most common fungal pathogens are Aspergillus species (60% to 90%) and Candida species (10% to 40%).[1] Stepwise multiplex polymerase chain reaction is more sensitive, rapid, and efficient than culture technique in differentiating bacterial otitis externa from fungal otitis externa.[9]

Tympanic membrane perforation may occur secondary to fungal otitis externa; a perforation rate of 6.75% has been reported.[8][10]​​​​ Perforation is common in otomycosis caused by Aspergillus flavus, Aspergillus tubingensis, and Candida albicans.[8]​ The perforation of tympanic membrane due to fungal otitis externa is smaller in size and may resolve with treatment. Some cases may require tympanoplasty.​​[10]​​​ 

Physical exam reveals swollen ear canal skin and discharge. Ear discharge may be thickened and black, gray, bluish green, yellow, or white.[1] The presence of black spores indicates Aspergillus niger as the causative organism.[1][3]​ White filamentous hyphae can often be seen. Microscopic exam and ear cultures can help establish the definitive diagnosis of otomycosis. Otomycosis should be suspected in patients who fail treatment with antibacterial agents.[3] Secondary fungal infection of the external auditory canal is well known after prolonged treatment with topical antibacterial agents.[11]​ 

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