Necrotising otitis externa

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Necrotising otitis externa begins in the external auditory canal but becomes a different clinical problem once infection invades surrounding tissues and bone. The canal may look less alarming than the pain history sounds. A patient who repeatedly attends because they cannot sleep, despite several prescriptions, deserves a fresh assessment of disease extent. The important decision is whether this remains superficial inflammation or now requires an urgent invasive-infection pathway.

Pseudomonas aeruginosa is a frequent cause, but the organism cannot safely be assumed from the diagnosis alone. Prior topical and oral antibiotics alter culture yield and resistance patterns; bacterial alternatives and fungal infection also occur. ENT, microbiology or infectious diseases, and radiology therefore contribute different information to one treatment plan. Local NHS antimicrobial protocols provide practical initial regimens, while individual cultures, renal function and response determine subsequent treatment.

Key points

Necrotising otitis externa is an invasive infection that can progress into temporal bone and the central skull base.
The historical term malignant otitis externa describes aggressive infection rather than a cancer diagnosis.
Suspect it when pain, especially at night, exceeds expectations for an apparently limited canal infection.
Diabetes and impaired immunity increase risk, but neither is required before making an urgent referral.
Obtain microbiology and appropriate tissue samples before antibiotics when the patient is stable enough for this.
CT defines bone and local anatomy; MRI adds information about soft tissue, marrow and intracranial disease.
Treatment needs systemic pathogen-directed antibiotics, canal care, analgesia and management of host factors.
A short course of ear drops cannot adequately treat established skull-base osteomyelitis.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Susceptible host

Diabetes, frailty and impaired immunity make invasive infection more likely. Assess glucose control and immunosuppressive treatment without using a normal glucose result to dismiss a convincing clinical presentation.

Organisms and previous exposure

Pseudomonas commonly drives disease, while other bacteria and fungi require different treatment. Recent ear drops, systemic antibiotics and previous resistant isolates must accompany the microbiology request.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Spread beyond canal skin
Infection crosses tissue planes around the external canal and reaches temporal bone. Persistent inflammatory injury produces pain and granulation, with osteomyelitis becoming the central problem rather than surface discharge alone.
2
Skull-base extension
Spread towards skull-base foramina can injure the facial and lower cranial nerves. New neurological signs therefore provide anatomical evidence of deeper disease and change the urgency and extent of investigation.
3
Slow recovery of bone
Clinical symptoms and laboratory trends may improve before structural imaging normalises. Conversely, relief of discharge can coexist with ongoing deep infection, so no single surface finding establishes cure.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Pain pattern and trajectory

Ask specifically about pain disturbing sleep, analgesic requirements and whether the apparent infection has improved with correctly delivered topical treatment. Document the trend instead of recording only a pain score today.

Canal and adjacent structures

Inspect for discharge, oedema and granulation, using specialist cleaning when necessary to obtain a meaningful view. Examine the pinna, mastoid, jaw movement and surrounding skin for alternative origins or spread.

Cranial nerve examination

Test facial movement and eye closure, then assess voice, palate, swallowing and tongue movement when appropriate. Record a baseline clearly so subsequent deterioration is detectable by another clinician.

Systemic and functional assessment

Check observations, hydration, glucose and nutritional intake. Lack of fever does not make a prolonged painful infection safe; assess whether home care is realistic when sleep, swallowing or medicine administration is compromised.

Red flags requiring action

Deep nocturnal pain continuing despite appropriate local treatment, particularly with diabetes or immunosuppression, should prompt urgent assessment for invasive disease.
Facial weakness, hoarseness, swallowing difficulty, tongue weakness or diplopia suggests spread beyond the canal and demands emergency specialist evaluation.
New severe headache, meningism, altered consciousness or a focal neurological deficit raises concern for intracranial infection or venous complications.
Granulation, bleeding or a persistent canal mass needs tissue assessment because infection and squamous malignancy can resemble one another.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Microbiology and tissue diagnosisFirst step
Why
Identify pathogens while investigating an important malignant mimic.
Interpretation and limitations
The current Lothian pathway requests blood cultures and deep bacterial and fungal samples with histology; an ear swab can supplement these. Obtain samples before treatment in stable patients, but never postpone urgent sepsis treatment for an operating-list sample.
02
CT of the temporal bones
Why
Define bony involvement and surrounding anatomical changes.
Interpretation and limitations
Discuss the imaging request with ENT and radiology so the relevant skull base is assessed. Absence of obvious erosion on an early scan should not close the case when clinical suspicion remains high.
03
MRI of the skull base and brain
Why
Assess soft tissue, marrow and possible intracranial extension.
Interpretation and limitations
MRI is especially useful when neurological signs or central spread are suspected. Imaging findings must be interpreted with the examination and microbiology rather than assigning treatment duration from one scan alone.
04
Baseline and serial laboratory tests
Why
Assess host factors, inflammatory activity and treatment safety.
Interpretation and limitations
Check FBC, CRP, renal function, electrolytes, liver tests and HbA1c, with additional immune-risk investigations when indicated. Trends support decisions, but neither an isolated marker nor its normalisation proves or excludes all active disease.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Severe superficial otitis externa

Marked canal oedema can cause substantial pain without bone invasion. Refractory symptoms, host risk and deeper clinical features justify specialist assessment rather than assuming that all severe pain is necrotising infection.

External auditory canal carcinoma

A friable lesion, bleeding and persistent unilateral symptoms can reflect squamous malignancy. Tissue should be sent for histology as well as infection studies when the specialist examines suspicious granulation.

Cholesteatoma with complications

Middle-ear keratin disease may cause chronic discharge, bone erosion and facial or vestibular symptoms. Careful otomicroscopy and imaging establish the origin and whether surgical clearance is required.

Fungal invasive infection

Fungal disease becomes particularly relevant with immune compromise or failure of antibacterial treatment. Deep fungal sampling and specialist interpretation are needed before selecting prolonged antifungal therapy.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Suspected diseaseEscalate and establish extentFirst stepEscalationPersistent deep pain or granulation raises concern for invasion.

1Arrange same-day ENT discussion and emergency admission for neurological signs, systemic instability or pain that cannot be safely managed.
2Assess airway, breathing, circulation and neurological state while giving appropriate analgesia and correcting clinically important physiological problems.
3Collect accessible cultures promptly and arrange otomicroscopy, tissue sampling and CT with MRI when deeper extension is suspected.
4Document previous antimicrobial exposure and coordinate an initial systemic treatment plan with the infection team.

02Confirmed infectionTreat the organism and hostClinical and investigative findings support invasive external ear infection.

1Select systemic treatment from the current local specialist pathway, then revise it to culture results and individual contraindications.
2Distinguish limited disease from cranial neuropathy, extensive bone involvement, venous disease, collections or intracranial extension before considering oral treatment.
3Provide specialist canal cleaning and topical adjuncts when indicated, alongside glucose optimisation, hydration, nutrition and sustained pain management.
4Agree a treatment and review schedule; the Lothian pathway uses at least six weeks, with final duration decided jointly from response.

03Continuing careMonitor response and recognise relapseThe patient requires prolonged therapy or planned outpatient treatment.

1Review pain trajectory, canal findings, cranial nerves and inflammatory markers together, checking for new features that demand further imaging.
2Arrange regular blood tests and medicine-specific monitoring, with a named service to respond to results and adverse effects.
3Use outpatient parenteral treatment only when clinical stability, suitable access, reliable monitoring and home circumstances have been established.
4At treatment completion explain relapse symptoms and provide rapid access to reassessment for renewed deep pain or neurological change.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

A systemic antipseudomonal option when susceptibility and the clinical assessment support oral treatment and other commonly recommended antibiotics are inappropriate.

Ciprofloxacin for selected adult necrotising infection

The February 2026 NHS Lothian specialist pathway considers 750 mg orally every 12 hours for uncomplicated disease with suitable renal function. Total treatment is at least six weeks in that pathway, with agent changes and stopping decided by ENT and infection specialists.

Apply MHRA systemic fluoroquinolone restrictions and explain potentially lasting tendon, nerve and psychiatric adverse effects. Avoid concomitant tizanidine; check renal dose adjustment, QT risks, interactions and pregnancy or breastfeeding suitability. Older age requires particular caution rather than automatic exclusion. Avoid concomitant corticosteroids where possible. Stop at a serious adverse reaction and obtain urgent prescriber advice to arrange alternative infection treatment.

An initial broad antipseudomonal regimen for complicated disease while microbiological information guides subsequent narrowing or modification.

Piperacillin/tazobactam for complicated adult disease

The current NHS Lothian initial regimen is 4.5 g intravenously every six hours for complicated infection, adjusted for renal impairment. This is specialist use for this indication; review cultures and IV need regularly within a prolonged total course, rather than prescribing a fixed six-week IV course.

Do not use with relevant penicillin hypersensitivity or previous acute severe allergy to another beta-lactam. Monitor renal function, potassium, blood count and liver tests during prolonged treatment; consider sodium load, methotrexate interactions and increased kidney-injury risk with vancomycin. Pregnancy and breastfeeding require an individual benefit-risk assessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Cranial neuropathy

Facial weakness may impair eye closure and require corneal protection. Lower cranial nerve involvement can compromise swallowing and airway safety, requiring immediate assessment rather than waiting for antibiotic response.

Intracranial and vascular spread

Meningitis, collections and venous thrombosis can develop as infection advances. Neurological deterioration requires emergency imaging and coordinated ENT, infection and neurosurgical input according to the structure involved.

Treatment toxicity and relapse

Long antimicrobial courses expose patients to renal, haematological and drug-specific adverse effects. Recurrence of deep pain after treatment should trigger prompt reassessment for relapse, resistance or an alternative diagnosis.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Track nocturnal pain and analgesic use alongside examination findings, because less discharge alone is an incomplete response measure.
Recheck cranial nerve function and swallowing whenever the patient reports a new voice, facial or eating problem.
Review renal function and electrolytes as treatment or hydration changes, and adjust antimicrobial dosing promptly when required.
During ciprofloxacin treatment ask directly about tendon pain, neuropathic symptoms and mental-state changes rather than waiting for spontaneous reporting.
Ensure the antimicrobial stop decision, follow-up arrangements and relapse instructions are understood by the patient and community clinicians.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

A name that can mislead

Explaining that malignant otitis externa is an older name for invasive infection avoids unnecessary assumptions about cancer while preserving the need to exclude an actual canal tumour.

Oral treatment still needs specialist ownership

Good oral bioavailability does not make necrotising infection suitable for an unreviewed community prescription. Route selection follows assessment of extent, susceptibility, absorption and safety.

Reconcile duration sources

The ciprofloxacin SmPC lists a broad duration range for malignant external otitis, while the current Lothian disease pathway specifies a minimum six-week total course. Follow the specialist disease plan and response rather than treating a label range as an automatic stop date.

Sampling after previous treatment

A negative superficial swab following several antibiotics is weak reassurance. Discuss the quality and timing of sampling, and whether deep tissue or fungal investigation is needed.

11Common pitfallsFrequent interpretation and management errors.

01
Labelling every persistent earache as uncomplicated swimmer’s ear can delay recognition of bone infection.
02
A normal temperature or initially unimpressive canal appearance does not safely exclude invasive disease.
03
Repeated topical prescriptions can delay definitive assessment and contribute to resistance or poor culture yield.
04
Do not generalise one local empirical regimen to fungal, resistant or intracranial infection without specialist review.