Otosclerosis

Otosclerosis
Classification and external resources
Chain of ossicles and their ligaments. (Stapes visible near center right.)
ICD-10	H80
ICD-9	387
OMIM	166800 605727
DiseasesDB	29289
eMedicine	article/994891 article/859760
MeSH	D010040

Otosclerosis is an abnormal growth of bone near the middle ear. It can result in hearing loss.^[1]

Clinical description

Otosclerosis can result in conductive and/or sensorineural hearing loss. The primary form of hearing loss in otosclerosis is conductive hearing loss (CHL) whereby sounds reach the ear drum but are incompletely transferred via the ossicular chain in the middle ear, and thus partly fail to reach the inner ear (cochlea). This usually will begin in one ear but will eventually affect both ears with a variable course. On audiometry, the hearing loss is characteristically low-frequency, with higher frequencies being affected later. Sensorineural hearing loss (SNHL) has also been noted in patients with otosclerosis; this is usually a high-frequency loss, and usually manifests late in the disease. The causal link between otosclerosis and SNHL remains controversial.

Approximately 0.5% of the population will eventually be diagnosed with otosclerosis. Post mortem studies show that as many as 10% of people may have otosclerotic lesions of their temporal bone, but apparently never had symptoms warranting a diagnosis. Caucasians are the most affected race, with the prevalence in the Black and Asian populations being much lower. In clinical practice otosclerosis is encountered about twice as frequently in females as in males, but this does not reflect the true sex ratio. When families are investigated it is found that the condition is only slightly more common in women.^[2] Usually noticeable hearing loss begins at middle-age, but can start much sooner. The hearing loss was believed to grow worse during pregnancy;^[3] but research shows that neither pregnancy nor breastfeeding may aggravate otosclerosis.^[4]

Genetics

The disease can be considered to be heritable, but its penetrance and the degree of expression is so highly variable that it may be difficult to detect an inheritance pattern. Most of the implicated genes are transmitted in an autosomal dominant fashion. One genome-wide analysis associates otosclerosis with variation in RELN gene.^[5]

Loci include:

Name	OMIM	Locus
OTSC1	166800	15q26.1
OTSC2	605727	7q
OTSC3	608244	6p
OTSC4	611571	16q
OTSC5	608787	3q22-q24
OTSC7	611572	6q13
OTSC8	612096	9p13.1-q21.11

Pathophysiology

The pathophysiology of otosclerosis is complex. The key lesions of otosclerosis are multifocal areas of sclerosis within the endochondral temporal bone. These lesions share some characteristics with Paget’s Disease, but they are not thought to be otherwise related. Histopathologic studies have all been done on cadaveric temporal bones, so only inferences can be made about progression of the disease histologically. It seems that the lesions go through an active “spongiotic” / hypervascular phase before developing into “sclerotic” phase lesions. There have been many genes and proteins identified that, when mutated, may lead to these lesions. Also there is mounting evidence that measles virus is present within the otosclerotic foci, implicating an infectious etiology (this has also been noted in Paget’s Disease).

CHL in otosclerosis is caused by two main sites of involvement of the sclerotic (or scar-like) lesions. The best understood mechanism is fixation of the stapes footplate to the oval window of the cochlea. This greatly impairs movement of the stapes and therefore transmission of sound into the inner ear (“ossicular coupling”). Additionally the cochlea’s round window can also become sclerotic, and in a similar way impair movement of sound pressure waves through the inner ear (“acoustic coupling”).

SNHL in otosclerosis is controversial. Over the past century, leading otologists and neurotologic researchers have argued whether the finding of SNHL late in the course of otosclerosis is due to otosclerosis or simply to typical presbycusis. There are certainly a few well documented instances of sclerotic lesions directly obliterating sensory structures within the cochlea and spiral ligament, which have been photographed and reported post-mortem. Other supporting data includes a consistent loss of cochlear hair cells in patients with otosclerosis; these cells being the chief sensory organs of sound reception. A suggested mechanism for this is the release of hydrolytic enzymes into the inner ear structures by the spongiotic lesions.

Diagnosis

Otosclerosis is traditionally diagnosed by characteristic clinical findings, which include progressive conductive hearing loss, a normal tympanic membrane, and no evidence of middle ear inflammation. The cochlear promontory may have a faint pink tinge reflecting the vascularity of the lesion, referred to as the Schwartze sign. Conductive hearing loss is usually secondary to impingement of abnormal bone on the stapes footplate. This involvement of the oval window forms the basis of the name fenestral otosclerosis. The most common location of involvement of otosclerosis is the bone just anterior to the oval window at a small cleft known as the fissula ante fenestram. The fissula is a thin fold of connective tissue extending through the endochondral layer, approximately between the oval window and the cochleariform process, where the tensor tympani tendon turns laterally toward the malleus.

Imaging is usually not pursued in those with uncomplicated conductive hearing loss and characteristic clinical findings. Those with only conductive hearing loss are often treated medically or with surgery without imaging. The diagnosis may be unclear clinically in cases of sensorineural or mixed hearing loss and may become apparent only on imaging. Therefore, imaging is often performed when the hearing loss is sensorineural or mixed. The mechanism of sensorineural hearing loss in otosclerosis is less well understood. It may result from direct injury to the cochlea and spiral ligament from the lytic process or from release of proteolytic enzymes into the cochlea.

A high-resolution CT shows very subtle bone findings. However, CT is usually not needed prior to surgery.

Otosclerosis on CT can be graded using the grading system suggested by Symons and Fanning.^[6] Grade 1, solely fenestral; grade 2, patchy localized cochlear disease (with or without fenestral involvement) to either the basal cochlear turn (grade 2A), or the middle/apical turns (grade 2B), or both the basal turn and the middle/apical turns (grade 2C); and grade 3, diffuse confluent cochlear involvement (with or without fenestral involvement).

Treatment

Further information: Hearing aids and Stapedectomy

Treatment of otosclerosis relies on two primary options: hearing aids (more recently including bone-conduction hearing aids) and a surgery called a stapedectomy. Hearing aids are usually very effective early in the course of the disease, but eventually a stapedectomy (or more frequently a variant called the stapedotomy) may be required for definitive treatment. Early attempts at hearing restoration via the simple freeing the stapes from its sclerotic attachments to the oval window were met with temporary improvement in hearing, but the conductive hearing loss would almost always recur. A stapedectomy consists of removing a portion of the sclerotic stapes footplate and replacing it with an implant that is secured to the incus. This procedure restores continuity of ossicular movement and allows transmission of sound waves from the eardrum to the inner ear. A modern variant of this surgery called a stapedotomy, is performed by drilling a small hole in the stapes footplate with a micro-drill or a laser, and the insertion of a piston-like prothesis. The success rate of either surgery depends greatly on the skill and the familiarity with the procedure of the surgeon.^[3] However, comparisons have shown stapedotomy to yield results at least as good as stapedectomy, with fewer complications, and thus stapedotomy is preferred under normal circumstances.^[7]

Other less successful treatments involve pharmaceuticals or orally ingested supplements. One is fluoride administration, which theoretically becomes incorporated into bone and inhibits otosclerotic progression. This treatment cannot reverse conductive hearing loss, but may slow the progression of both the conductive and sensorineural components of the disease process. Otoflour is one such widely used medicine, comprising sodium fluoride. Recently, some success has been claimed with a second such treatment, bisphosphonate medications that inhibit bone destruction.^[8][9][10] However, these early reports are based on non-randomized case studies that do not meet standards of clinical trials.^[11] There are numerous side-effects to both pharmaceutical treatments, including occasional stomach upset, allergic itching, and increased joint pains which can lead to arthritis.^[12] In the worst case, bisphosphonates may lead to osteonecrosis of the auditory canal itself.^[13] Finally, neither approach has been proven to be beneficial after the commonly preferred method of surgery has been undertaken.

Famous patients

The renowned German composer Beethoven was theorized to suffer from otosclerosis, although this is controversial.^[14] Victorian journalist Harriet Martineau gradually lost her hearing during her young life, and later medical historians have diagnosed her with probably suffering from otosclerosis as well.^[15] Howard Hughes the pioneering American aviator, engineer, industrialist, and film producer also suffered from otosclerosis.^[16] Frankie Valli, lead singer of The Four Seasons, suffered from it in the 1970s, forcing him to "sing from memory" in the latter part of the decade (surgery restored most of his hearing by 1980).^[17] Tampa Bay Lightning forward Steve Downie suffers from otosclerosis.^{[citation needed]} Alexandra of Denmark, Queen of the United Kingdom suffered from it.^{[citation needed]} Adam Savage, host of MythBusters, uses a hearing aid due to otosclerosis.^[18]

References in popular culture

During the first three seasons of the CBS TV series CSI: Crime Scene Investigation, Gil Grissom suffered from otosclerosis, which he inherited from his mother. At the end of the show's third season, Grissom underwent a stapedectomy to correct it.

Dwayne Schneider, the building superintendent on "One Day at a Time", undergoes a stapedectomy to correct otosclerosis in one episode.

References

1. ^ "otosclerosis" at Dorland's Medical Dictionary
2. ^ Morrison AW (1970) Otosclerosis: a synopsis of natural history and management. British medical journal 2(5705):345-348.
3. ^ ^{a b} de Souza, Christopher; Glassock, Michael (2003). Otosclerosis and Stapedectomy: Diagnosis, Management & Complications. New York, NY: Thieme. ISBN 1588901696 
4. ^ Lippy WH, Berenholz LP, Schuring AG, Burkey JM (October 2005). "Does pregnancy affect otosclerosis?". Laryngoscope 115 (10): 1833. doi:10.1097/01.MLG.0000187573.99335.85. PMID 16222205. http://www3.interscience.wiley.com/journal/121607933/abstract. 
5. ^ Schrauwen I, Ealy M, Huentelman MJ, Thys M, Homer N, Vanderstraeten K, Fransen E, Corneveaux JJ, Craig DW, Claustres M, Cremers CW, Dhooge I, Van de Heyning P, Vincent R, Offeciers E, Smith RJ, Van Camp G (February 2009). "A Genome-wide Analysis Identifies Genetic Variants in the RELN Gene Associated with Otosclerosis". Am. J. Hum. Genet. 84 (3): 328. doi:10.1016/j.ajhg.2009.01.023. PMC 2667982. PMID 19230858. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2667982. 
6. ^ Lee TC, Aviv RI, Chen JM, Nedzelski JM, Fox AJ, Symons SP: CT grading of otosclerosis. American Journal of Neuroradiology, 2009 August, 30(7):1435-1439. Epub 2009 March 25.
7. ^ Thamjarayakul T, Supiyaphun P & Snidvongs K, Stapes fixation surgery: Stapedectomy versus stapedotomy, Asian Biomedicine, 4(3): 429-434, 2010.
8. ^ Brookler K (2008). "Medical treatment of otosclerosis: rationale for use of bisphosphonates". Int Tinnitus J 14 (2): 92–6. PMID 19205157. 
9. ^ http://www.freshpatents.com/-dt20090716ptan20090181108.php?type=description
10. ^ http://books.google.com/books?id=9s7RQ74WgikC&pg=PA65&lpg=PA65&dq=Biphosphonate+otosclerosis&source=bl&ots=FW3U7hq0wr&sig=SLAZ4zS1Fo8NRCslUlH8wJIY8kE&hl=ru&ei=PA8dS9v8GJrImgOVyZHZAw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAoQ6AEwAA#v=onepage&q=Biphosphonate%20otosclerosis&f=false
11. ^ Chole RA & McKenna M, Pathophysiology of otosclerosis, Otology & Neurotology, 22(2): 249-257, 2001.
12. ^ Otosclerosis at the American Hearing Research Foundation Chicago, Illinois 2008.
13. ^ Polizzotto MN, Cousins Polizzotto & Schwarer AP, Bisphosphonate-associated osteonecrosis of the auditory canal, British Journal of Haematology, 132(1): 114, 2005.
14. ^ The Ludwig van Beethoven biography, http://www.kunstderfuge.com/bios/beethoven.html
15. ^ Mary Jo Deegan, "Making Lemonade: Harriet Martineau on Being Deaf, p. 41-58 in Harriet Martineau: Theoretical and Methodological Perspectives, NY, NY: Routledge 2001
16. ^ Charles Higham, Howard Hughes: The Secret Life
17. ^ Fred Bronson, The Billboard Book of Number One Hits (3rd edition), Billboard Books 1992. ISBN 0-8230-8298-0
18. ^ http://twitter.com/donttrythis/status/1701444283

External links

• NIH/Medline
• NIH/NIDCD
• Otosclerosis Patient Accounts and Support - Patient Support