Inflammatory cast of the tympanic membrane after acute otitis media

Abstract Objective: To describe a relatively unknown clinical entity – inflammatory cast of the tympanic membrane after acute otitis media – and its simple out-patient treatment. Study design: Retrospective review of case series. Setting: Subspecialty practice at a tertiary hospital. Patients: Seven patients diagnosed previously with acute otitis media with perforation or otitis externa, and with persistent ear discomfort. Methods: Retrospective chart review. Results: The patients presented with weeks to months of persistent hearing loss after acute otitis media with perforation or acute otitis externa. Visits to their primary care physicians had been uninformative. After comparison of the affected and unaffected tympanic membranes, a thin, hard cast was identified and removed from the affected tympanic membrane. Improvement in hearing was documented in the three patients who underwent audiometric testing; the remainder had subjective improvement without audiometric evaluation. Conclusion: Otolaryngologists should be aware of the possibility of an inflammatory cast of the tympanic membrane following acute otitis media with perforation or otitis externa, and should carefully compare the unaffected and affected ears in such cases. Treatment – removal of the rigid cast – is both simple and effective.


Introduction
Patients often present with external auditory canal obstruction caused by products of the canal micro-environment: cerumen, keratosis obturans and cholesteatoma. 1 Disturbances of cerumen accumulation are related to the well documented epithelial migration of the skin of the tympanic membrane and external auditory canal. 2 In cases of keratosis obturans, histological examination reveals tightly packed keratinaceous lamellae without cell bodies. 3 While keratosis obturans circumferentially envelopes the entire external auditory canal, external auditory canal cholesteatoma is a focal disorder with subadjacent osteonecrosis and focal epithelial loss. 1 Also, while keratosis obturans typically forms a plug-like cast which fills the entire canal, the products of cholesteatoma are not always completely obstructive.
We report here a new clinical entity distinct from any previously described. We present a patient series, with illustrations, of a cast of the tympanic membrane composed of inflammatory products, presenting after acute otitis media or otitis externa. The distinguishing features of this cast are: formation after acute otitis media with perforation or otitis externa; a painless, 'plugged' sensation with or without audiometric evidence of hearing loss; and appearance of a thin, hard layer which resembles normal morphology and which coats the tympanic membrane and external canal. These patients often present after previous, frustrating visits to other medical providers. The uninformed physician may easily overlook their problem, while the informed one easily resolves it.

Case series
This study was approved by our Institutional Review Board. Table I outlines the clinical details for seven patients with a typical inflammatory cast, both male and female adults, aged between 29 and 73 years. All patients reported an initial painful otitis media with perforation or otitis externa, which resolved with antibiotics but which left them with continued discomfort from a plugged sensation. Typically, patients had seen two to three doctors before the correct diagnosis was made. The key to successful diagnosis was the otolaryngologist's awareness of the possibility of an inflammatory cast, together with rigorous comparisons with the contralateral tympanic membrane and external auditory canal. Those patients who underwent audiometric testing pre-and post-cleaning demonstrated improved pure tone thresholds; patients who did not undergo testing reported subjective hearing improvement.
The most seriously affected patient was a 36-year-old woman who had seen 3 doctors in 24 weeks since suffering acute otitis media with perforation. She presented with hearing loss and ear discomfort, seeking a second opinion, 3 days before a scheduled ossiculoplasty. Figure 1 shows this patient's pre-operative temporal bone computed tomography, and illustrates the inflammatory cast on the external surface of the tympanic membrane. Removal of this cast resolved the patient's 40 dB conductive hearing loss. Figure 2 shows a typical inflammatory cast of the tympanic membrane, identified in another patient after weeks of drops and antibiotics. Figure 3 shows the tympanic membrane midway through cast removal. Figure 4 illustrates the cleaned tympanic membrane, with cast fragments remaining on the external auditory canal skin. Figure 5 shows the inflammatory cast with a notch indicating the position of the malleus.
The photomicrograph reproduced as Figure 6 shows a largely acellular, rigid eschar with embedded neutrophils and lymphocytes. Loose orthokeratin is present on the surface. Despite the inflammatory cast's gross appearance, reminiscent of sloughed skin, it is composed largely of an acellular exudate with sparse embedded inflammatory cells.

Discussion
The presented cases all involved a previous episode of acute otitis media with perforation or otitis externa, which successfully resolved but left the patient with a hearing deficit. Each patient's hearing loss improved dramatically after careful visual examination under procedural microscopy and subsequent removal of an inflammatory cast on the tympanic membrane.
• Acute otitis media with perforation and acute otitis externa often lead to hearing loss after resolution • Careful comparison with the contralateral tympanic membrane may reveal an inflammatory cast covering the affected tympanic membrane • Removal of this cast may dramatically improve hearing This cast matched the size and shape of the tympanic membrane, suggesting a possible mechanism for its development. Specifically, we hypothesise that a serous exudate with inflammatory cells coats the tympanic membrane and the external canal skin. This hardens to form a fibro-exudative cast which is uncomfortable and which also impedes tympanic membrane vibration.
The key features enabling identification of this inflammatory cast of the tympanic membrane are: a normal contralateral ear, a high index of clinical suspicion for the problem, and resolution of hearing loss upon meticulous cleaning of the tympanic membrane.