Malignant Otitis Externa

By

Dr. T. Balasubramanian M.S. D.L.O.

 




Malignant otitis externa is  a inflammatory disorder involving the external auditory canal caused by psuedomonas organism.  Majority of these patients are elderly diabetics.  This condition is termed as malignant otitis externa because of its propensity to cause complications.  Hence the term malignant must not be constured in a histological sense.

History:

1838 - Toulmousch reported the first case of otitis externa
1959 - Meltzer reported a case of pseudomonas osteomyelitis of temporal bone
1968 - Chandler discussed the various clinical features and described it as a distinct clinical entity

The effectiveness of present day antibiotics in the management of this condition should provoke the physicians to abandon the term malignant while describing this condition.


Epidemiology:
The typical patient with malignant otitis externa is an elderly diabetic, with males outnumbering females by twice the number.  This could be due to the possibility of males being more prone to secrete wax which are more acidic in nature.  Malignant otitis externa is very rare in children, if present it will be associated with malnutrition or HIV infection.

Pathophysiology:

Malignant otitis externa is knwon to affect the external auditory canal and temporal bone.  The causative oraganism being pseudomonas aeruginosa.  These patients are invariably elderly diabetics.  This disorder usually begins as otitis externa and progresses to involve the temporal bone.  Spread of this disease occurs through the fissures of Santorini and osteo cartilagenous junction.  This disorder could be caused by a combination of poor immune response and peculiar characteristics of the offending microbe.
Immunity is reduced in patients with :
1. Diabetis mellitus
2. Blood cancer
3. HIV infections
4. Patients on anticancer drugs

It should also be remembered that diabetic patients have impaired phagocytosis, poor leukocytic response, and impaired intracellular digestion of bacteria.  Diabetic patients secrete wax which has less lysozyme content than normal thereby reducing the effectiveness of wax as an antimicrobial agent.

Pseudomonas aeruginosa is a gram negative aerobe with polar flagella.  It is found on the skin.  It invariably behaves like an opportunistic pathogen.  The pathogenicity of this organism is due to ability to secrete exotoxin and various enzymes like lecithinase, lipase, esterase, protease etc.  Since this organism is cloathed by a mucoid layer it is resistant to digestion by macrophages.

Clinical features:
The patient gives history of trivial trauma to the ear often by ear buds, followed by pain and swelling involving the external auditory canal.  Pain is often the common initial presentation.  It is often severe, throbbing and worse during nights.  It needs increasing doses of analgesics.  On examination granulation tissue may be seen occupying the external canal. It often begins at the bony cartilagenous junction of the external canal.  Discharge eminating from the external canal is scanty and foul smelling in nature.  When the discharge is foul smelling it indicates the onset of osteomyelitis.  Ironically the patient does not have fever or other constitutional symptoms.

Otoscopy: Reveals granulation tissue at the bony cartilagenous junction.  The ear drum is usually normal.  The external auditory canal skin is soggy and edematous.
Cranial nerve palsies are common when the disease affects the skull base.  The facial nerve is the most common nerve affected.  As the disease progresses the lower three cranial nerves are affected close to the jugular foramen.
Intracranial complications like meningitis and brain abscess are also known to occur.

 

 










Figure showing granulation tissue in the external canal

 







Figure showing malignant otitis externa patient with facial palsy


Spread of infection:
1. Inferiorly through the stylomastoid foramen to involve the facial nerve.
2. Anteriorly to the parotid
3. Posteriorly to the mastoid and sigmoid sinus
4. Superiorly to the meninges and brain
5. Medially to the sphenoid
6. Spread through vascular channels are also common

Role of imaging:

    * Conventional radiology is of no use.
    *
    * CT scan is useful in assessing bone destruction.
    *
    * MRI is useful in assessing soft tissue involvement.
    *
    * Radionucleotide scans with Technetium 99 helps in assessing bone involvement

Imaging alogrithm in these patients are:
1. TC99 scan to seek evidence of bone involvement
2. If this is positive CT scan and MRI scan is a must to rule out bone and soft tissue involvement
3. Serial Ga 67 scans to assess the efficacy of treatment modality.

Levenson's criteria for diagnosis of malignant otitis externa:

    * Refractory otitis externa
    *
    * Severe nocturnal otalgia
    *
    * Purulent otorrhoea
    *
    * Granulation tissue in the external canal
    *
    * Growth of Pseudomonas aeruginosa from external canal
    *
    * Presence of diabetes and and other immunocompromised state

Staging & classification:


  Stage

  Ga67

  TC99

  Extent of Disease

 I

  +

  -

  Soft tissue (Necrotising Otitis)

  II

Ear & Mastoid
(Skull base osteomyelitis) 

  III

  +

Extensive skull base osteomyelitis 


Treatment:

Extensive surgical procedures have failed miserably to cure this condition.  The role of surgery is confined to only exclusion of malignancy by biopsy.  Wound debridement is a possibility in advanced cases.

Medical management:
Carbenicillin, Pipercillin, Ticarcillin can be used.  Third and forth generation cephalosporins can be used.
Ciprofloxacillin in doses of 1.5 g  - 2.5 g /day in divided doses can be administered for a period of 2 weeks.
Gentamycin can also be administered parenterally in doses of 80 mg iv two times a day in adults. 



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