Malignant Otitis Externa: Symptoms, Diagnosis and Treatment

Malignant otitis externa is a severe and sometimes deadly infection of the external ear's soft tissues and surrounding structures that progresses quickly to the periosteum and skull base bone.

Toulmouche originally characterized the illness in 1838, and it is regarded as the disease's first case report. Pseudomonas aeruginosa is the most common causative pathogen, especially in immunocompromised people with diabetes, HIV, leukemia, granulocytopenia, anemia, or immunosuppressive drugs. 

In addition, various fungal species, including Aspergillus and Candida, have been identified as causative agents. Several cases of methicillin-resistant Staphylococcus aureus (MRSA) have been documented, and the number of MOE causal agents, including Klebsiella and Proteus mirabilis, is increasing.

Coagulation and tissue necrosis are produced by microangiopathy of microscopic blood vessels. The most common clinical manifestations are acute otalgia, otorrhea, hearing loss, and granulation polyps. The facial nerve is the most commonly damaged cranial nerve, however, the glossopharyngeal, vagus, accessory, or hypoglossal nerves can also be affected.

The diagnosis was made using anamnesis, clinical examination, audiological evaluation, microbiological analysis of ear swabs, and a CT (computed tomography) scan of the temporal bone, skull base, and endocranium. Notably, diagnostic criteria have changed over time. A recent thorough study found 27 unique sets of diagnostic criteria for this condition.

The main treatment for MOE is long-term antibiotic medication. Other treatment options include regular monitoring of blood glucose and inflammatory markers, as well as frequent local debridement of necrotic tissue. Hyperbaric oxygen chambers have recently become more widely used as therapy options. 

Notably, surgery has a limited function in the treatment of MOE. Even though MOE has been recognized for decades, there is little evidence to support its management. Thus, in the absence of convincing facts to guide decision-making, clinicians rely on their own expertise and judgment.

Incidence and Epidemiology Of Malignant Otitis Externa

It is a rare disorder occurring predominantly in immunocompromised patients. Elderly individuals with diabetes mellitus(uncontrolled) are the most commonly affected. It is reported in various other immuno-compromised states, including myeloid malignancies, pharmacologic immunosuppression, and HIV/AIDS. It is less likely to occur in immuno-competent patients.

Microbiology Of Malignant Otitis Externa

Most cases are caused by Pseudomonas aeruginosa, followed by Staphylococcus aureus.  Alpha hemolytic streptococcus can cause this infection but usually results in necrotizing otitis externa which is very similar to malignant otitis externa. Malignant otitis externa is more aggressive than necrotizing otitis externa.

 Aspergillus species are the most common fungal pathogens to cause this disorder. Interestingly, many of the case reports of Aspergillus-induced malignant otitis externa have been in non-diabetic individuals. Fluoroquinolone-resistant Pseudomonas is an increasing problem and is particularly frustrating because fluoroquinolones are the only enterally administered antibiotics with antipseudomonal activity.

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Pathology Of Malignant Otitis Externa

It is the End-stage of a severe infection that originates from the external auditory canal and progresses through cellulitis, chondritis, periostitis, osteitis, and finally osteomyelitis It has also been reported following surgery to the temporal bone. It mainly affects the Haversian system of compact bone and involvement of the pneumatized portion of the temporal bone is a late finding.

Malignant Otitis Externa disseminates through the Haversian canals and vascularized spaces of the skull base. As this progresses along the base of the skull, the facial nerve (stylomastoid foramen), hypoglossal nerve (hypoglossal canal), the abducens and trigeminal nerves (petrous apex), the glossopharyngeal, vagus, and spinal accessory nerves (jugular foramen) may be involved. 

Cranial neuropathy has classically been considered to have a poor prognosis. Spreads out of the cartilaginous external auditory canal through the fissures of Santorini, congenital defects in the floor of the external auditory canal.

Spread of Infection Of Malignant Otitis Externa

• Inferiorly, it goes through the stylomastoid foramen to involve the facial nerve.
• Anteriorly, it will spread to the parotid 
• Posteriorly, it goes to the mastoid and sigmoid sinus. 
• Superiorly, it reaches to the meninges and brain.
• Medially, it will go to the sphenoid via the petrous apex .

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Clinical Features Of Malignant Otitis Externa

Patients are initially seen with long-standing otalgia, which can be severe, and otorrhea. Pain is often the common initial presentation. It is often severe, throbbing, and worse during the night. The discharge from the external canal is scanty and foul-smelling.

When the discharge is foul-smelling, it indicates the onset of osteomyelitis. Ironically, the patient does not have a fever or other constitutional symptoms. Granulation tissue emerges from the ear canal floor at the bony-cartilaginous junction, which is the distinguishing feature. 

In its initial stages, the infection is confined to the skin and soft tissues of the ear canal. As it progresses, the infection involves the bony structures of the temporal bone. At its most advanced stages, it extends beyond the temporal bone along the skull base or intracranially or both. 

The facial nerve is the most common cranial nerve involved, with paralysis resulting from involvement at the stylomastoid foramen. Further progression leads to the involvement of the lower cranial nerves at the jugular foramen and hypoglossal canal.

Intracranial spread results in headaches, fever, neck stiffness, and altered levels of consciousness.

Differential Diagnosis of Malignant Otitis Externa

• Carcinomas of the EAC.
• Chronic granulomatous disease.
• Paget disease 
• Fibrous dysplasia 
• Nasopharyngeal carcinomas 

Diagnosis Of Malignant Otitis Externa

Your doctor will perform a physical exam to determine if you have malignant otitis externa. The evaluation will include a complete health history. This will assist your doctor in determining underlying disorders that may affect your immune system.

During the exam, your doctor will inspect your ear to see whether there is an infection. Apart from this the following investigations will be performed:

• Blood test to find if inflammatory markers like ESR and CRP are elevated.
• Cultures and sensitivity should be obtained to help in selecting appropriate antibiotics.
• As carcinoma of the EAC mimics many features of Malignant Otitis Externa, a biopsy is requisite to rule out carcinoma.
• Radiological investigations
  • HRCT scan of the Temporal Bone.
  • MRI 
  • Technetium 99 Bone Scan 
  • Gallium 67 citrate and Indium III labeled leukocyte scan.

HRCT Scan of the Temporal Bone 

The first investigation should be the HRCT scan of the Temporal bone for the findings of bony erosion.

• This investigation shows even small cortical erosion of the tympanic bone and is a useful first-line test.
• Disadvantages of CT include an under-appreciation of the soft tissue and intracranial extent of disease and the inability to distinguish infection from malignancy.
• Because normalization of bone anomalies may never occur despite infection elimination, CT has limited ability to evaluate therapeutic response. 

CT petrous bone demonstrating mastoiditis and granulation tissue at the external auditory canal in cases of necrotizing otitis externa.

An axial CT image demonstrates the previous mastoidectomy cavity (arrow). The right middle ear is opacified and deteriorated anteriorly, and it connects to the right middle cranial fossa.

The right labyrinthine portion of the facial nerve canal has enlarged (arrow). The tegmen tympani has deteriorated. The middle ear is opaque, and soft tissue may be seen within the right external auditory canal. The erosion occurs on the upper surface of the petrous bone (arrows).

MRI 

This study ignores minor bone deterioration. It is excellent at detecting soft tissue changes and may require dural augmentation. These are more likely to resolve with therapy, therefore MRI is more useful in tracking the progression of illness.

Axial T1 weighted image. There is a loss of the normal high signal within the right petrous bone (compare this to the normal high signal within the clivus and left petrous apex).

Axial T2 weighted fat saturated image shows an abnormal intermediate signal within the right petrous bone. This is seen to surround the right intra-petrous carotid artery and extends to encroach on the right middle cranial fossa.

T2 weighted fat-saturated image shows the very bright signal of fluid within the right mastoidectomy cavity, and there is an intermediate signal of the petrous bone medial to this. Compared to the normal low signal on the left side.

T1 post-contrast. The enhancing tissue displaces and compresses the right temporal lobe. The enhancement includes non-enhancing fluid within the mastoidectomy cavity.

Coronal T1 post gadolinium shows enhancing inflammatory tissue elevating and compressing the right temporal lobe. There is a thin line of reactive dural enhancement extending up the lateral aspect of the temporal lobe. The cerebral substance does not.

Technetium 99M Bone Scan

It Shows areas of osteoblastic activity and is highly sensitive to bony infection. Traditional planar imaging or single photon emission computed tomography (SPECT) can be used.  SPECT enables precise anatomic localization and can detect regions of bone involvement before a CT scan reveals structural alterations. Because bony repair persists long after the infection has resolved, it is not used to follow the response to treatment.

Gallium-67 Citrate And Indium-111-Labeled Leukocyte Scans

It is a radioisotope taken up by the neutrophils(cells of acute inflammation) Initially if gallium-67 is positive later it becomes negative then it indicates that there is a possibility of resolution of infection. It shows the areas of inflammatory cell activity. 

These tests are sensitive, and uptake values return to normal quickly with the resolution of infection, making them useful in following response to treatment. False-positive findings might occur due to irritated soft tissues around the bone.

Serial gallium-67 SPECT scans with simultaneously acquired CT images superimposed to allow anatomical localization. Scan A was an early post-treatment scan with minimal tracer uptake; scan B, taken approximately two months later, shows increased uptake in keeping with deterioration.

Lavensons criteria for diagnosing malignant otitis externa 

• Refractory otitis externa.
• Severe nocturnal otalgia.
• Purulent otorrhoea.
• There is the presence of pseudomonas and granulation tissue in the external auditory canal.
• Diabetes or an immunocompromised state.
• Positive Tc-99 bone scan of the temporal bone.

Clinicopathological Classification System

• Stage 1: Stage 1: Clinical evidence of malignant otitis externa, with soft tissue infection limited to the external auditory canal, but a Tc-99 bone scan is negative.
• Stage 2: Soft tissue infection beyond the external auditory canal with a positive Tc-99 bone scan.
• Stage 3: It can be the same as a positive Tc-99 bone scan and spread beyond the canal, but there is cranial nerve paralysis.
  • 3a: single cranial nerve 
  • 3b: multiple cranial nerves involved. 
• Stage 4: Cranial extensions such as Meningitis, empyema, sinus thrombosis, or brain abscess. 

Treatment Of Malignant Otitis Externa

It is important to perform debridement of the granulation tissue and rigorous control of blood sugar. Topical and systemic antibiotics should be directed against the pseudomonas. Surgical intervention is avoided as it may hasten the spread of infection and is only used after failure of a more prolonged, conservative approach.

• Antibiotic therapy- Early infections may be treated solely with an oral fluoroquinolone (most commonly ciprofloxacin) except in cases of resistant organisms. In more advanced stages, parenteral antibiotics may be indicated initially with discharge of the patient home on oral fluoroquinolones. 
  • Aminoglycosides (e.g., tobramycin) and antipseudomonal ß-lactam antibiotics, including piperacillin, ticarcillin, or ceftazidime, may be used. The total duration of treatment is typically 6 weeks, or as indicated by the results of radiologic studies and clinical response.
• Hyperbaric Oxygen Therapy- It is commonly employed in facilities with convenient access to hyperbaric chambers. In cases of cerebral spread where the illness is recurring or antibiotic-resistant, using both hyperbaric oxygen and antibiotics concurrently may be recommended. 
• Surgical Treatment- Because the condition affects both the fascial and vascular planes, surgical intervention is not suggested. Biopsies can be taken and any abscesses drained. Decompression is not recommended for facial nerve palsy. Surgical resection should be reserved for cases in which bone involvement is resistant to therapy and to abort a rampant or progressive infection.

 In these cases, surgical intervention would include a wide resection of the bony skull base, including the stylomastoid foramen and jugular bulb, together with the introduction of viable, vascularized tissue (e.g., temporalis muscle flap or microvascular free tissue transfer) into the bed. Commonly performed surgery is  Subtotal or total petrosectomy

Complications Of Malignant Otitis Externa

Below are mentioned some of the complications Of malignant otitis externa:

• Meningitis.
• Abscess.
• Sagittal, dural, and cavernous sinus thrombosis.

How can I Prevent Malignant Otitis Externa?

The best strategy for preventing malignant otitis externa is to treat all swimmer's ear infections until they heal. This involves following your doctor's recommendations and completing the whole course of antibiotics.

Additionally, if your immune system is compromised, you should take care to protect your health. If you have diabetes, this involves maintaining stable blood sugar levels. If you have HIV, you will need to take medication to prevent the virus from reproducing in your body. Protecting your health is critical for boosting your immune system and avoiding illnesses.

Factors Indication of Poor Prognosis

• Facial Nerve involvement
• Additional cranial nerve involvement (9/10/11)
• B/L ear involvement
• Non-cranial nerve involvement but neurological involvement in terms of meningitis
• Extensive granulation & edema in EAC
• Aspergillus infection

Hope you found this blog helpful for your ENT Residency Otology Preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs. 

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