What are the diagnostic procedures and treatment options for otosclerosis (abnormal bone growth in the middle ear)?

Diagnosis of Otosclerosis

Primary Diagnostic Approach

The diagnosis of otosclerosis is primarily clinical, based on history, pneumatic otoscopy, pure-tone audiometry, and tympanometry, with high-resolution CT of the temporal bone (HRCT) serving as the definitive imaging modality when confirmation is needed. 1, 2

Clinical Presentation and History

• Progressive conductive hearing loss is the hallmark presentation, typically bilateral and slowly progressive 2, 3
• Tinnitus occurs in approximately 73% of patients 4
• Vertigo or vestibular symptoms may be present in active disease 5
• Family history is often positive, as otosclerosis affects genetically predisposed individuals 2
• Onset typically occurs in young to middle-aged adults 2, 3

Physical Examination

• Pneumatic otoscopy should be performed as the primary examination method, which typically shows a normal-appearing tympanic membrane with normal mobility 1
• Schwartz sign (pinkish retrotympanic lesion) may be visible on otoscopy in active otosclerosis, representing increased vascularity over the promontory 1

Audiometric Evaluation

Pure-Tone Audiometry

• Conductive hearing loss pattern with air-bone gap, particularly at low frequencies 4, 6
• Carhart notch (bone conduction dip at 2 kHz) is present in approximately 80% of cases, though it is not specific for otosclerosis 4, 6
• Air-bone gap differences between low and high frequencies are diagnostically useful: if the difference between 0.25 kHz and 4 kHz air-bone gap is greater than 10 dB, otosclerosis is more likely than ossicular discontinuity 6
• Bone conduction thresholds may show involvement at 250 Hz, 1 kHz, and 2 kHz in more advanced disease 4

Tympanometry

• Type A tympanogram (normal) is seen in 68% of cases 4
• Type As tympanogram (reduced compliance) occurs in only 22% of cases 4
• Static compliance measurements help differentiate otosclerosis from incudostapedial disconnection 6

Acoustic Reflex Testing

• Reversed ipsilateral acoustic reflex at 0.5 kHz and 2 kHz is a significant finding 6
• Negative contralateral acoustic reflex helps distinguish otosclerosis from other causes of conductive hearing loss 6
• Gelle test (negative in 92% of otosclerosis cases) assesses stapes fixation, though it is less commonly performed in modern practice 4

Imaging Studies

High-Resolution CT of Temporal Bone (HRCT)

• HRCT without IV contrast is the imaging modality of choice for confirming otosclerosis when clinical diagnosis is uncertain 1, 7
• Positive CT findings are present in approximately 46% of cases, showing demineralization around the oval window, fissula ante fenestram, or cochlear capsule 4, 2
• Bone algorithm reconstructions are essential to visualize the subtle bony changes characteristic of otosclerosis 7
• IV contrast is not beneficial because the diagnosis relies on evaluating bone contour and density changes 1, 7
• Standard head CT is inadequate and should not be used, as it lacks the resolution to detect otosclerotic foci 1, 7

MRI

• MRI may play a role in identifying active otospongiotic lesions and assessing cochlear involvement, particularly when considering medical management or in cases with significant sensorineural component 2
• MRI is insufficient alone for diagnosing otosclerosis due to limited bony detail 1, 7

Differential Diagnosis Considerations

The combination of audiometric findings, impedance testing, and imaging is essential to distinguish otosclerosis from other causes of conductive hearing loss:

• Incudostapedial disconnection: Shows air-bone gap difference between 0.25 kHz and 4 kHz less than 10 dB (sensitivity 81.1%, specificity 55.0% for this cut-off) 6
• Ossicular chain abnormalities: HRCT demonstrates ossicular erosion, fusion, or displacement 1, 7
• Superior semicircular canal dehiscence: HRCT with Pöschl plane reconstructions shows bony dehiscence 1
• Congenital middle ear anomalies: HRCT reveals structural abnormalities 1

Diagnostic Algorithm

1. Obtain detailed history focusing on progressive hearing loss, tinnitus, family history, and vestibular symptoms 2, 3
2. Perform pneumatic otoscopy to assess tympanic membrane appearance and mobility, looking for Schwartz sign 1
3. Conduct comprehensive audiometry including pure-tone testing with air and bone conduction, calculating air-bone gaps at multiple frequencies 4, 6
4. Perform tympanometry and acoustic reflex testing to assess middle ear compliance and reflex patterns 4, 6
5. Order HRCT temporal bone without contrast when diagnosis is uncertain or surgical planning is needed 1, 7, 2
6. Consider MRI if cochlear otosclerosis is suspected or medical management is being considered 2

Common Pitfalls to Avoid

• Do not rely on Carhart notch alone for diagnosis, as it lacks specificity and is absent in 20% of cases 4, 6
• Do not order standard head CT instead of dedicated temporal bone HRCT, as it lacks adequate resolution 1, 7
• Do not assume Type As tympanogram is required for diagnosis, as most patients (68%) have Type A tympanograms 4
• Do not overlook the need for multiple diagnostic modalities in combination, as no single test is definitive 4, 3, 6