Necrotizing/Malignant Otitis Externa

Question 1

Hallmark Finding of Malignant Otitis Externa

Answer 1

Granulation tissue protruding through the floor of the ear canal at the Boney-Cartilaginous junction.

Question 2

What is the Incidence of Malignant Otitis Externa?

Answer 2

MOE is rare

Question 3

What is Malignant Otitis Externa?

Answer 3

MOE is an aggressive, potentially fatal infection originating in the external auditory canal, with progressive spread along the soft tissues and bone of the skull base, ultimately involving intracranial structures.

Question 4

What is the Other Name for Malignant Otitis Externa?

Answer 4

MOE is more accurately known as Necrotizing Otitis Externa

Question 5

Epidemiology of Malignant Otitis Externa

Answer 5

MOE occurs primarily in immunocompromised patient’s:

1) Elderly patient’s with Diabetes are the most commonly affected patients
2) MOE has been reported in other immunocompromised states to include
- Myeloid malignancies
- Pharmacologic immunosuppression
- HIV/AIDS
3) MOE can also occur in immunocompetent patients

Question 6

Microbiology of Malignant Otitis Externa

Answer 6

1) Most cases are caused by Pseudomonas aeriginosa
2) Staph aureus is the next most common causative agent
3) Aspergillus is the most common fungal agent causing MOE, but more exotic molds have also been identified

Question 7

Clinical Manifestations of Malignant Otitis Externa

Answer 7

1) Patients are initially seen with long-standing otalgia, which can be severe, and otorrhea.
2) The Hallmark finding is granulation tissue protruding through the floor of the ear canal at the bony-cartilaginous junction.
3) In its initial stages, the infection is confined to the skin and soft tissues of the ear canal. As the infection progresses, it involves the bony structures of the temporal bone. In its most advanced stages, it extends beyond the temporal bone along the skull base or intracranially, or both.

Question 8

What is the most commonly affected Cranial Nerve in Malignant Otitis Externa?

Answer 8

The Facial Nerve - FN paralysis results from involvement at the stylomastoid foramen.

Question 9

What Other Cranial Nerves Can Be Affected By Malignant Otitis Externa?

Answer 9

Progression of MOE leads to involvement of the lower cranial nerves at the jugular foramen and hypoglossal canal.

Question 10

What are the signs of intracranial spread in Malignant Otitis Externa?

Answer 10

Headache

Fever

Neck stiffness

Altered level of consciousness

Question 11

How should Malignant Otitis Externa Be Worked Up?

Answer 11

Early diagnosis of MOE requires a high index of suspicion.

1) When it is suspected, bacterial and fungal cultures should be obtained at the time of the initiation of treatment.
2) High resolution CT of the Temporal Bone - easy to get, relatively inexpensive and is a useful first-line test.
- Bony changes of MOE may never return to normal so CT is not good for following progression/resolution of dz
3) MRI scan can miss subtle bony erosion, it is better for showing soft tissue changes and dural involvement. These changes resolve with treatment making MRI more useful for following the course of the disease.
4) Tc-99 Bone Scanning shows areas of osteoblastic activity and is very sensitive for bony infection. Can be used when the clinical suspicion for MOE is high, but the CT scan is negative. Because bony repair persists long after the infection has resolved, Tc 99 scanning is not used to follow response to treatment.
5) Gallium-67 Citrate and Indium-111 labeled Leukocyte scans show areas of inflammatory cell activity. These tests are sensitive and return to normal quickly with resolution of infection. This makes them useful for following the course of the disease. Greater diagnostic accuracy may be obtained by simultaneous aquisition of a SPECT Tc-99 bone scan and Indium-111 labeled leukocyte scan.

Question 12

Treatment of Malignant Otitis Externa

Answer 12

Early diagnosis and aggressive medical therapy is important in cure of MOE:

1) Antipseudomonal antibiotics is the cornerstone of treatment.
- Early infections can be treated solely with an oral Fluoroquinolone (usually Cipro) except in cases of resistant organisms.
- More advanced disease, IV abx are required initially with discharge on oral Cipro.
- Total duration of treatment is usually 6 weeks.
2) HBO treatment has not been proven to help treat MOE
3) Surgery only rarely indicated. Should only be used when bone involvement is resistant to therapy - this would include wide resection of the skull base including the stylomastoid foramen and jugular bulb, together with the introduction of viable vascularized tissue (temporalis flap or free flap) transfer into the surgical bed.