eMedicine Specialties > Otolaryngology and Facial Plastic Surgery > External Ear Diseases

External Ear, Malignant External Otitis: Differential Diagnoses & Workup

Author: Brian Nussenbaum, MD, FACS, Associate Professor, Vice Chair for Clinical Affairs, Co-director of Fellowship in Microvascular Head/Neck Oncology, Department of Otolaryngology-Head and Neck Surgery, Washington University School of Medicine
Coauthor(s): Peter S Roland, MD, Professor, Department of Neurological Surgery, Professor and Chairman, Department of Otolaryngology-Head and Neck Surgery, Director of Clinical Center for Auditory, Vestibular and Facial Nerve Disorders, Chief of Pediatric Otology, University of Texas Southwestern Medical Center; Adjunct Professor of Communicative Disorders, University of Texas School of Human Development
Contributor Information and Disclosures

Updated: May 19, 2009

Differential Diagnoses

Malignant Tumors of the Temporal Bone

Workup

Laboratory Studies

  • Leukocyte count
    • The leukocyte count is usually normal or mildly elevated.
    • A left shift is not commonly found.
  • Erythrocyte sedimentation rate
    • Erythrocyte sedimentation rate (ESR) is invariably elevated, with an average of 87 mm/h.
    • It begins to decrease within 2 weeks of initiating therapy but takes many months to return to normal.
    • ESR can be used to support the clinical diagnosis since acute external otitis or ear canal malignancy usually does not cause a rate elevation in this lab test.
  • Serum chemistry
    • Patients with known diabetes need an evaluation of the serum chemistry to determine if the infection is affecting their baseline glucose intolerance.
    • Patients without a history of diabetes should be tested for glucose intolerance.
  • Culture and sensitivities from the external auditory canal
    • Culture from the ear drainage should be performed ideally before antimicrobial therapy is initiated.
    • The most common causative organism is P aeruginosa (95%). This organism is an aerobic, gram-negative rod. Pseudomonas species has a mucoid coating that deters phagocytosis. Exotoxins (ie, exotoxin A, collagenase, elastase) can cause tissue necrosis, and some strains produce a neurotoxin that may be partially responsible for cranial neuropathies.
    • Less common organisms identified include Aspergillus and Proteus species, Candida species, Staphylococcus aureus, and Staphylococcus epidermidis.

Imaging Studies

  • These are important adjuncts for determining the presence of osteomyelitis, the extent of disease, and response to therapy.
  • Technetium Tc 99 methylene diphosphonate bone scanning is based on binding to osteoblasts.
    • This scan depicts as little as a 10% increase in osteoblastic activity. However, this test is not specific since tumors or bony dysplasias, in addition to osteomyelitis, can cause osteoblastosis.
    • It is useful in the initial evaluation because a positive finding in the correct clinical context can lead to confirmation of the diagnosis.
    • The test is not useful for assessing the response to therapy since results remain persistently positive long after clinical improvement because of continuous bone remodeling and reformation.
    • This test may also have limited usefulness for patients with a prior history of mastoiditis or otologic surgery.
    • The application of single-photon emission computed tomography (SPECT) technology has improved the poor spatial resolution traditionally associated with this test.
  • Gallium citrate Ga 67 scan is very sensitive but is not specific because gallium binds to actively dividing cells, including inflammatory cells, tumor cells, and osteoblasts.
    • Uncertainty is possible regarding whether a positive test result represents an inflammatory condition, soft tissue, or bone disease.
    • This test is most helpful when used as a monitor of successful treatment. Improvement of a positive test result correlates with therapeutic response.
    • A baseline test is usually obtained at the initial diagnosis for comparison with follow-up studies during treatment.
    • A quantitative comparison of the lesion to the nonlesion side may improve the interpretation of these studies for distinguishing acute external otitis from malignant external otitis (MEO) and for determining the efficacy of therapy.
    • The application of SPECT technology has improved the poor spatial resolution traditionally associated with this test.
  • Indium In 111–labeled leukocyte scan attempts to provide the same sensitivity as a gallium citrate Ga 67 scan but is more specific to an inflammatory process.
    • It does not appear to provide an improvement in scintigraphic technique for helping to establish the diagnosis.
    • It may be better than gallium citrate Ga 67 scans for assisting in establishing the correct timing of disease resolution.
    • This test can be unreliable for imaging chronic osteomyelitis in other areas of the body. Thus, the accuracy of this application needs further study.
  • CT scanning and MRI are both useful for evaluating the anatomic extent of soft tissue inflammation, abscess formation, and intracranial complications.
    • CT scanning fails to diagnose early osteomyelitis because 30-50% of bone destruction is required to detect osteomyelitis by CT scanning.
    • MRI provides poor bone resolution.
    • The soft tissue manifestations regress on CT scanning and MRI with response to therapy.
    • Bone changes remain persistently abnormal on CT scans for at least one year and are not well demonstrated by MRI studies. Thus, neither of the tests can be used to determine osteomyelitis resolution.
    • Most authors advocate obtaining a CT scan with the initial evaluation for all patients, whereas Benecke advocates obtaining this test selectively for patients with cranial neuropathy, extensive bone changes on technetium scan, or poor clinical response to treatment. Grandis et al and Okpala et al support obtaining a CT scan early in the diagnostic/treatment algorithm. Peleg et al showed that there is a correlation between clinical course and the extent of anatomical areas involved as measured on initial CT scan findings.6  
    • MRI and CT scanning are equally sensitive in detecting the soft tissue extent of the disease, but MRI is more sensitive for detecting intracranial complications.

Procedures

  • Obtain a biopsy of the external auditory canal to exclude carcinoma or other etiologies.

Histologic Findings

Nadol described the histopathology of 2 temporal bones affected by malignant external otitis (MEO). The infection did not spread through the pneumatized air tracts of the temporal bone. Rather, it spread along the vascular and fascial planes on exiting the temporal bone through the external auditory canal osseocartilaginous junction or fissures of Santorini. The otic capsule appeared to be resistant to the disease process. Linthicum described histopathologic findings in 5 temporal bones. Extensive destruction in the wall of the bony external auditory canal and osteomyelitic destruction of the wall of the fallopian canal in the descending portion of the facial nerve was seen. The infection spread beneath the otic capsule to erode the wall of the carotid canal and then extended into the central skull base.

Staging

  • Levenson et al, Corey et al, Benecke, and Davis et al have proposed staging systems for malignant external otitis (MEO).7,8,9
    • These staging systems are generally based on extent of soft tissue/bony involvement or development of neurologic complications.
    • None of these staging systems has been widely adopted.

More on External Ear, Malignant External Otitis

Overview: External Ear, Malignant External Otitis
Differential Diagnoses & Workup: External Ear, Malignant External Otitis
Treatment & Medication: External Ear, Malignant External Otitis
Follow-up: External Ear, Malignant External Otitis
Multimedia: External Ear, Malignant External Otitis
References
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References

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Further Reading

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Keywords

malignant external otitis of the external ear, external ear, malignant external otitis, MEO, invasive external otitis, necrotizing external otitis, progressive external otitis, skull base osteomyelitis, ear infection, pseudomonal osteomyelitis of the temporal bone, Pseudomonas aeruginosa, P aeruginosa, diabetes, malignant external otitis

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Contributor Information and Disclosures

Author

Brian Nussenbaum, MD, FACS, Associate Professor, Vice Chair for Clinical Affairs, Co-director of Fellowship in Microvascular Head/Neck Oncology, Department of Otolaryngology-Head and Neck Surgery, Washington University School of Medicine
Brian Nussenbaum, MD, FACS is a member of the following medical societies: Alpha Omega Alpha, American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Head and Neck Society, Phi Beta Kappa, Society of University Otolaryngologists-Head and Neck Surgeons, and Triological Society
Disclosure: Nothing to disclose.

Coauthor(s)

Peter S Roland, MD, Professor, Department of Neurological Surgery, Professor and Chairman, Department of Otolaryngology-Head and Neck Surgery, Director of Clinical Center for Auditory, Vestibular and Facial Nerve Disorders, Chief of Pediatric Otology, University of Texas Southwestern Medical Center; Adjunct Professor of Communicative Disorders, University of Texas School of Human Development
Peter S Roland, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Otolaryngic Allergy, American Academy of Otolaryngology-Head and Neck Surgery, American Auditory Society, American Laryngological Rhinological and Otological Society, American Neurotology Society, American Otological Society, North American Skull Base Society, and Society of University Otolaryngologists-Head and Neck Surgeons
Disclosure: Alcon labs Honoraria Speaking and teaching; GSK Honoraria Speaking and teaching; Advanced Bionics Honoraria Board membership; Cochlear corp Honoraria Board membership; Med El corp travel grants Consulting

Medical Editor

Jack A Shohet, MD, Associate Clinical Professor, Department of Otolaryngology-Head and Neck Surgery, University of California Irvine; Otolaryngologist, Shohet Ear Associates Medical Group, Inc
Jack A Shohet, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American Medical Association, American Neurotology Society, American Tinnitus Association, and California Medical Association
Disclosure: Envoy Medical Consulting fee Consulting

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Gerard J Gianoli, MD, Clinical Associate Professor, Department of Otolaryngology-Head and Neck Surgery, Tulane University School of Medicine; Vice President, The Ear and Balance Institute; Chief Executive Officer, Ponchartrain Surgery Center
Gerard J Gianoli, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Surgeons, American Neurotology Society, American Otological Society, Society of University Otolaryngologists-Head and Neck Surgeons, and Triological Society
Disclosure: Nothing to disclose.

CME Editor

Christopher L Slack, MD, Otolaryngology-Facial Plastic Surgery, Private Practice, Associated Coastal ENT; Medical Director, Treasure Coast Sleep Disorders
Christopher L Slack, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Medical Association
Disclosure: Nothing to disclose.

Chief Editor

Arlen D Meyers, MD, MBA, Professor, Department of Otolaryngology-Head and Neck Surgery, University of Colorado School of Medicine
Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Head and Neck Society
Disclosure: Covidien Corp Consulting fee Consulting; US Tobacco Corporation unstricted gift unknown

 
 
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