eMedicine Specialties > Pediatrics: Surgery > Otolaryngology

Otosclerosis: Differential Diagnoses & Workup

Author: 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, School of Human Development.
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Updated: Oct 16, 2008

Differential Diagnoses

Hearing Impairment
Osteogenesis Imperfecta

Other Problems to Be Considered

Differential diagnosis of otosclerosis should include other causes of conductive hearing loss.

• In the context of a normal CT scan result, the only way to make a definitive diagnosis of otosclerosis is by exploratory tympanotomy and palpation of the stapes.
• A history of recurrent otitis media suggests an ossicular discontinuity due to incus necrosis or ossicular chain fixation due to tympanosclerosis.
• Congenital stapedial footplate fixation is present at an earlier age than juvenile otosclerosis. Congenital footplate fixation is generally detectable at age 3 years, whereas juvenile otosclerosis is rarely if ever detected before age 10 years.
• Paget disease can be diagnosed based on its manifestation in areas other than the otic capsule. Osteogenesis imperfecta, similarly, is diagnosed on the basis of associated symptoms (eg, blue sclerae, multiple fractures).
• A newly diagnosed cause of conductive hearing loss is dehiscent semicircular canal syndrome. This disorder is classically associated with Tullio phenomenon (vertigo and/or nystagmus associated with loud noises). Diagnosis depends on CT scans that reveal a dehiscent superior semicircular canal when the appropriate symptomatology is present. Tullio phenomenon should be objectively documented. Vestibular evoked myogenic responses are frequently altered in this disease.
• Other problems to be considered include the following:
  • Ossicular discontinuity
  • Fixation of the head of the malleus or incus
  • Congenital stapes fixation
  • Paget disease
  • Superior semicircular canal dehiscence syndrome

Workup

Imaging Studies

• In otosclerosis, fine-cut CT scanning can often reveal deposition of new bone in the area of the round or oval window and/or otosclerotic foci within other portions of the labyrinthine capsule and cochlea. The outlining of the resultant labyrinth is sometimes referred to as a "halo sign."

Other Tests

• Diagnosis depends on a combination of audiometric testing and historical features. An audiometric evaluation reveals conductive hearing loss with absent stapedius reflex. Historically, patients report a relatively slowly progressive hearing loss in the absence of significant infectious ear disease or otologic trauma. Several other indications that can support the diagnosis include the following:
  • The Carhart notch is a frequent audiometric to otosclerosis but is also seen in other types of conductive hearing loss. It consists of the appearance of a sensorineural hearing loss (SNHL) of 20-30 decibels (dB) at approximately 2000 cycles per second. The Carhart notch does not represent a genuine SNHL because it disappears after successful stapedectomy.
  • Speech discrimination is usually excellent.
  • A type A tympanogram with very low compliance may be noted. Sometimes termed a stiffness curve, this is often referred to as an A_s pattern. This configuration is occasionally present but is frequently absent.
  • Fine-cut CT scanning can often show deposition of new bone in the area of the round or oval window and/or otosclerotic foci within other portions of the labyrinthine capsule and cochlea.
  • Vestibular testing should be included when dizziness is present. Although no findings are characteristic for otosclerotic inner ear syndrome, findings suggestive of either superior semicircular canal dehiscence or of Ménière disease alter treatment plans.
• Audiometric testing is the principal study required for the management of otosclerosis. Both air and bone conduction must be evaluated. If the clinical manifestations are all due to footplate fixation, audiography reveals a purely conductive loss. If involvement of the otic capsule in other areas causes hair cell injury, SNHL is also detected. No explicit criteria have been developed that allow the clinician to definitively distinguish SNHL caused by otosclerosis from hearing loss due to other causes.
• Diagnosis of cochlear otosclerosis (ie, SNHL due to otosclerosis) generally requires a halo sign on fine-cut CT scanning or SNHL that is more advanced than expected from presbycusis, in the presence of some sign of stapedial involvement (eg, conductive hearing loss from footplate fixation, abnormalities of stapedius reflex testing).

Histologic Findings

• The otospongiotic phase of the disorder is characterized by bone resorption. Several cell types, such as histiocytes, osteocytes, and osteoblasts, participate in this process.
• Bone resorption begins around existing vessels with consequent enlargement of vascular channels. Resultant hypervascularization, or a red blush, seen on the medial wall of the inner ear through the tympanic membrane is the Schwartze sign. This hypervascularization can sometimes be visualized during clinical otoscopy.
• As the otospongiotic phase continues, a ground substance is deposited as a replacement for resorbed bone. The result is new spongy bone that has a blue appearance on histologic staining. These blue areas seen on hematoxylin and eosin (H and E) preparations are referred to as blue mantles of Manasse.

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