What is malignant otitis externa? How do you classify? Describe its pathology, presentation and management options.
Malignant otitis externa is an aggressive and potentially life threatening infection of the soft tissues of the external ear and surrounding structures, quickly spreading to involve the periosteum and bone of the skull base.
It is classified on the basis of clinicopathology:
Stage
1 → clinically evidence of malignant otitis externa with infection of soft tissues beyond the external auditory canal but negative Tc -99 scan.
2 → Soft tissue infection beyond external auditory canal c positive Tc- 99 bone scan.
3 → As above but c cranial nerve palsies
32 → single
3b → multiple
4 → Meningitis, empyema, sinus thrombosis and brain abscess
Pathology
The term malignant otitis externa was coined because of its mortality.
The infection may develop in pre-existing chronic otitis externa.
Malignant otitis externa is the end stage of a severe infection that originate from the external auditory canal.
The infection starts as the cellular of EAC and progress through chondritis →periostitis → and → finally osteomyelitis
Infection can be spread from:
The fissures of santorini → parotid involved
Tympanomastoid suture → Facial nerve and other cranial nerve.
It effects the Haversian system of the compact bone and the involvement of the pneumatized portion of the temporal bone is a late finding.
The otic capsule is usually spared.
Multiple micro abscesses are found at surgery of postmortem.
Presentation (PEGOSAR)
Pain
Exudates (otorrhroea)
Granulations
Oedema of external auditory canal
Positive bone scan
Micro abscess at surgery
Resistance to local therapy
Diabetes/ Other immunocompromised state
DIAGNOSIS
Clinical diagnosis
Pseudomonas aeruginosa culture
Positive bone scan:
Tc-99 → useful for detecting initial bony involvement
Gallium citrate → more sensitive monitoring.
CT-scan → extend of bone destruction
SPECT → more expensive
MRI → differentiate between a truly malignant process rather than inflammation.
MANAGEMENT
Treatment of underlying predisposing factor e.g. control of diabetes
Aural toilet to control granulation and improve local pain control (Use of the topical antibiotics is controversial.)
Systemic antibiotics:
Anti Pseudomonas antibiotics for at least 6 weeks to 3 months.
IV ciprofloxacin in doses of 1.5 g – 2.5 g /day in divided doses can be administered for a period of 2 weeks with or without aminoglycoside and/or ceftazidine
Monotherapy: Injection Ceftazidine
Gentamycin can also be administered parenterally in doses of 80 mg iv two times a day in adults.
Others:
Oral rifampicin
Tobramijin
Implantable gentamycin beads- if oral therapy is contraindicated.
Surgery: Indication
If patient is deteriorating clinically
Removal of all infected tissue, sequestra collected pus and
Debridement of necrotized and granulating tissue.
Occasionally necrotic bone, diseased cartilage and if necessary parotid gland has to be removed.
Radical mastoidectomy should be avoided if the air cell system is not involved.Extensive surgical procedures does not appear successful 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.
Protection