Otosclerosis
- Article Author:
- Nowera Zafar
- Article Author:
- Zohaib Jamal
- Article Editor:
- Moien AB Khan
- Updated:
- 8/15/2020 12:25:16 AM
- For CME on this topic:
- Otosclerosis CME
- PubMed Link:
- Otosclerosis
Introduction
Otosclerosis (oto, “of the ear,” and sclerosis, “abnormal hardening of body tissue”), also known as otospongiosis, is an abnormal bone remodeling in the middle ear. The normal dense endochondral layer of the bony otic capsule in the labyrinth is replaced by irregularly laid spongy bone leading to the fixation of the stapes.[1] Otosclerosis commonly causes conductive deafness presenting with a normal tympanic membrane. Furthermore, depending upon the foci of involvement on the bony labyrinth, otosclerosis can be asymptomatic or can present as a neurosensory loss. Nevertheless, otosclerosis has an effect on the functioning of the middle and the inner ear.
Etiology
The exact etiology of otosclerosis is still unclear. The multiple etiologies that have been postulated include:
Anatomical: The most commonly affected part seems to be the fissula ante fenestram, where the remnants of the embryonic cartilage persist.[2]
Genetic: Many loci on chromosomes 6p, 9p, 1q, 3q, 6q, 7q, 15q, and 16q have been identified. In an open genome-wide analysis, a new locus on chromosome 7q22.1 has also been found. Besides, different genes that are involved including type I collagen (COL1A1 gene), TGF-beta 1 (BMP 2 and BMP 4 genes), angiotensin II (AGT M235T and ACE I/D genes), sex hormones, autoimmune reaction, human leucocyte antigen, inflammatory and regulatory cytokines, parathyroid hormone and expression of parathyroid hormone-related peptides receptors, and oxidative stress have also been regarded as causes of otosclerosis.[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]
Hereditary: In more than half of the patients presenting with otosclerosis, there is a positive family history. Also, patients with a positive family history have an earlier onset of otosclerosis. Genetic studies show that an autosomal dominant mode of inheritance with reduced penetrance (40%) and a variable expressivity is found in most of the cases.[18][19][18][20][21]
Sex: The prevalence of otosclerosis is more in women compared to men suggesting the role of sex hormones.[22]
Ethnicity: Otosclerosis is more common in Whites. However, it is rarer in the Black population.[23][24]
Age: Hearing loss is more commonly seen between the second and the third decade.[25]
Pregnancy: Pregnancy does worsen deafness in osteosclerosis; however, the relationship of pregnancy with otosclerosis is still controversial.[26]
Viral Infections: The role of measles virus infection in the pathogenesis of otosclerosis has been postulated. Measles virus ribonucleic acid has been detected in the footplate of stapes on electron microscopy and immunohistochemical studies. Moreover, vaccination against measles virus is a protective factor against otosclerosis because of the significant decrease in the incidence of vaccinated populations.[27]
In addition to the above factors, menopause, trauma, or a major operation have been associated with either causing or aggravating otosclerosis.[26][28]
Epidemiology
The prevalence of clinical otosclerosis is around 0.04% to 1% in the Whites.[18] Histological otosclerosis can be as high as 10% compared to clinical otosclerosis in Whites.[29][30] Furthermore, the prevalence of histological otosclerosis in Blacks is 1%, and in the Asian population is around 5%.[18] Otosclerosis is an early adult-onset disease with an incidence greater in women compared to men in a ratio of 2:1.[19][18] Otosclerosis starts in the twenties and thirties but usually does not cause a hearing loss until after the fourth decade.[31]
Pathophysiology
Multiple etiological factors are involved with such bony dyscrasias. Bone remodeling occurs locally within the otic capsule with bone resorption followed by bone deposition in the focus lesions.[32] Though such remodeling occurs in other bones of the body, it is physiologically not seen in the otic capsule. The lesion is a replacement of normal bone with sclerotic or spongiotic bone. The histological disease progresses in stages.
Osteolytic osteocytes appear on the leading edge of the lesion, and connective tissue sheets can be seen replacing the bone. Dense sclerotic bone formation in areas of the previous resorption signifies the late phase of otosclerosis. The result is disorganized bone, the increased number of osteocytes, and widened marrow spaces consisting of vessels and other connective tissue.
Marrow spaces are later replaced by dense sclerotic bone with narrow vasculature and few recognizable Haversian systems. Pleomorphism is due to the normal coexistence of both stages of otosclerosis in any single temporal bone. The initiating lesion often neighbors the fissula ante fenestram and expand via vascular channels.[33] In the majority of cases, lesions are limited to the anterior oval window and affect its pathology by calcification of annular ligament or by involving the stapes. Both processes result in conductive hearing loss.
Histopathology
Grossly, otosclerotic foci are chalky white, greyish, or yellowish in appearance. If the osteosclerotic centers are active and progressing rapidly, then they appear red due to increased vascularity.
Microscopically, the dense enchondral layer of the otic capsule appears to contain the spongy bone. In immature active lesions of otosclerosis, there is plenty of marrow and vascular spaces with numerous osteoblasts and osteoclasts. Also, there is a large quantity of cement substance that stains bluish-grey (blue mantles) with hematoxylin-eosin stain.[34] Less vascularity and more bone and fibrillar substance than cementum are seen in the mature foci, and it stains red.
History and Physical
The most frequent presentation of patients with clinical otosclerosis is hearing loss. Also, tinnitus and vertigo can occur. It is vital to take a detailed clinical history. Usually, the patient with otosclerosis presents with bilateral hearing loss as the most common symptom that has been gradually worsening over many years. Typically, it starts in one ear, and as it progresses, it involves the other ear.
The initial symptoms include being unable to hear the low-frequency sounds, such as a whisper. Also, the patients may give a history that they can hear well in noisy surroundings termed as "paracusis willisii." Though it is not specific of otosclerosis, it is indicative of conduction deafness. The patients themselves may speak in a low volume and a monotonous voice. As the disease becomes extensive, tinnitus may worsen as well. Dizziness is usually mild, but as the disease progresses, dizziness may deteriorate, mimicking Meniere disease.[35]
On physical examination, otoscopy may reveal minimal details and may be normal. However, with active otosclerosis or cochlear otosclerosis, increased promontory vascularity may be visible through the eardrum and is clinically termed as the Schwartz sign.[36] However, this finding is only apparent in around 10%.[37][38]
Evaluation
Tuning Fork Test
The tuning fork test shows a negative Rinne test. Webers test is lateralized to the ear with severe conductive loss.
Audiometry and Tympanometry
Pure tone audiometry shows lower frequency loss of air conduction. However, bone conduction is normal. A bone conduction dip in thresholds of 20-30 dB and more pronounced at 2000 Hz is called Carhart notch. After stapedectomy, Carhart notch disappears. A Carhart notch may also be present in cases of incus or malleus fixation and incudostapedial joint detachment.[39] Also, mixed hearing loss can be seen in audiometry in patients with otosclerosis. The discrimination score is normal speech audiometry. Generally, tympanometry is normal in early otosclerosis. However, in severe cases, a flattening or a stiffness curve may be observed, indicating low compliance of the ossicular chain and tympanic membrane. Tympanometry can further differentiate otosclerosis from the pathologies with low resonance, such as a disconnection in the middle ear bone system.
High-Resolution Computed Tomography (CT)
High-resolution computed tomography (CT) of the temporal bones is the standard choice to diagnose otosclerosis.[40] It aids in identifying and ruling out other causes of deafness. In more than 80% of the cases, the fenestral foci, located in the area anterior to the oval window, can be found. Also, the thickening of the footplate and the round window involvement can guide the treatment. Retrosternal focus visualized as a double halo sign is seen with cochlear otosclerosis.[41] A grading system suggested by Symons and Fanning can be used for CT grading of otosclerosis.[42]
Treatment / Management
Medical Management:
Medical treatment is primarily aimed to halt the progress or to prevent disease progression. There is no medical therapy that is curative for otosclerosis. Though sodium fluoride is prescribed to slow the progression of the otosclerosis, the efficacy is still controversial.[43][44]
Bisphosphonates exert antiresorptive action, by inducing osteoclastic apoptosis. Bisphosphonates, in particular, newer generation bisphosphonates are commonly used to treat otosclerosis with promising results.[32][45]
Bilateral hearing aids are also used in many patients, either alone or in combination with other treatments.
Surgical Management:
The treatment of choice is stapedotomy or stapedectomy, along with placement of a prosthesis. Surgical treatment for otosclerosis has shown good results, irrespective of the surgical approaches. Revision surgery, if indicated for otosclerosis, is met with mixed success and maybe needed with facial nerve damage, persistent vertigo, or failure to improve the hearing. Though surgery is beneficial to restore hearing, in a few of the patients, there may be a need to use hearing aids after surgical treatment.[46][1][47][48]
Differential Diagnosis
Other conditions of the ear which present with the conductive deafness and from which otosclerosis should be differentiated include:
- Serous otitis media
- Adhesive otitis media
- Congenital stapes fixation
- Meniere disease
- Tympanosclerosis
- Attic fixation of head of the malleus
- Ossicular discontinuity
Prognosis
More than 90% of the patients experience considerable improvement in their hearing ability after the surgery. Occasionally, there may be a few cases in which the surgery yields no particular benefits. Worsening of the hearing loss has also been reported rarely. Improved results have been recorded when making use of laser techniques and vein grafts.
Additionally, there is a chance of recurrence of the conductive hearing loss, which may be due to the displacement of the prosthesis out of its original position. The cause is likely to be the contraction of collagen in the neomembrane formed between the prosthesis and the labyrinth. It has been observed that revision surgery is less successful than the first surgery.[49][50]
Complications
Untreated otosclerosis can gradually progress towards considerable hearing loss, but complete deafness is unusual.
Surgical correction of otosclerosis can result in a total sensorineural loss in the operated ear, but it is an infrequent occurrence. Complications of the surgery that may arise are injury of the facial nerve and tinnitus. Although short-lived, an unpleasant taste can also occur, owing to the proximity of the chorda tympani when performing surgery. Moreover, about the effect of the introduced prosthesis, specific adverse outcomes that may arise are the erosion and necrosis of the incus and granuloma formation.[49]
Deterrence and Patient Education
Patients should be advised for follow up in case of a family history of otosclerosis. It is essential to communicate with the patient. Furthermore, pregnancy can trigger otosclerosis, and those patients who have hearing problems during pregnancy should be investigated for otosclerosis.
Pearls and Other Issues
Otosclerosis is an early adult-onset disease that can cause significant disability and morbidity due to hearing loss. Improving health professional understanding of how to evaluate and treat this condition promptly will lead to better patient outcomes.
Enhancing Healthcare Team Outcomes
Otosclerosis is a progressive disease and gets worse with the passage of time, leading to complete hearing loss, thus causing disability. Interprofessional communication and care coordination between otolaryngologist, surgeon, providers, occupational therapist, psychotherapist, and the nurses will enhance the overall outcomes for the patients.
(Click Image to Enlarge)
The External Ear, External and middle ear; Right side, Attic, Incus, Malleus, Tympanic cavity, Tensor tympani, Auditory Tube
Contributed by Gray's Anatomy Plates
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The Middle ear or Tympanic Cavity, Right tympanic membrane as seen through a speculum, Long crus of incus, Conc of light, Manubrium of malleus
Contributed by Gray's Anatomy Plates
(Click Image to Enlarge)
The Auditory Ossicles, Left malleus, A; From behind, B; From within
Contributed by Gray's Anatomy Plates