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Synonyms: OTSC, otospongiosis
This is a genetically mediated metabolic dysplasia, affecting the bony tissue of the otic capsule (the skeletal elements enclosing the inner ear mechanism), and the auditory ossicles. The otic capsular bone is unusual in that, following early development, it does not undergo extensive remodelling. In otosclerosis there is a pathological increased bony turnover leading to sclerosis and failure of the sound conduction mechanism, due to ankylosis of the stapes footplate in the fenestra ovalis of the cochlea. This produces a slowly progressive conductive hearing impairment. In some cases, the disease process may also extend from bony tissue to the cochlea itself, causing a mixed conductive and sensorineural hearing loss.
It is inherited in an autosomal dominant fashion with variable penetrance.The interplay of genes with environmental factors is thought to be critical in the phenotypic activation of genetic susceptibility. There is considerable genetic heterogeneity, with at least seven loci identified via linkage studies, as well as rare monogenic forms. Environmental factors implicated in the aetiology of otosclerosis include oestrogens, fluoride and viral infections such as measles. Measles virus RNA has been found in the footplate of otosclerosis specimens but there are other cases of stapes fixation that appear not to be associated with measles infection. It is likely that a number of different pathways underlie the development of otosclerosis, with different genetic and environmental risk factors contributing to a similar final disease outcome.
Histological otosclerosis is present in around 2.5% of people.However, the clinical manifestations are seen in only about 0.3%. The annual incidence is thought to be declining as measles becomes a rarer infection, due to recent childhood immunisation programmes against the disease. In Germany, decrease in hospital treatment for otosclerosis has been observed since the introduction of measles vaccination.[6, 7]
- Race - it is more common in white and Asian populations.
- Sex - it is more commonly diagnosed in women, although not sex-linked and no sex differences found in pathological series.
- Age - it usually presents between teen years and middle age (typically between the ages of 15 and 35). However, the average age for having surgery is rising; it is thought that the childhood measles vaccination programme is altering the epidemiology of the condition.
- Positive family history - there is approximately 1/4 risk if one parent is affected; 1/2 risk if both parents are affected.
- Drinking non-fluoridated water - controversial.Some studies suggest fluoridation of water does not prevent the development of otosclerosis.
- The hearing loss may progress at a variable rate and tinnitus tends to worsen as the hearing loss worsens.
- The hearing loss is usually low tone in nature - deep, male voices may be particularly difficult to discriminate.
- Vestibular symptoms are usually absent but may cause mild dizziness in some cases.
- Very occasionally, vestibular involvement can manifest as severe, paroxysmal rotatory nystagmus akin to Ménière's disease.
- Patients may have low-volume speech (enhanced bone conduction leads to the perception of their own speech as 'loud').
- Auroscopy is usually normal.
- About 10% show Schwartze's sign - reddish-blue discolouration over promontory and oval window niche, due to vascular hyperaemia of immature abnormal bone.
- Tuning fork tests (Rinne's and Weber's tests) reveal conductive pattern deafness in the majority of cases.
- Where the cochlea is involved there may be a mixed conductive/sensory pattern of hearing loss.
- Other middle ear pathology - eg, chronic suppurative otitis media, chronic serous otitis media (glue ear).
- Damage to ossicles, particularly the long process of incus in chronic infection.
- Congenital stapes fixation which is non-progressive and usually noted in the first decade of life.
- Ménière's disease in cases with severe vestibular symptoms.
- Postinfective tympanosclerosis usually follows chronic infection.
- Paget's disease of bone can cause a clinically indistinguishable syndrome, but will usually have other features of the disease. Ask about change in hat size and bony pain. Histologically, Paget's disease of bone can be differentiated from otosclerosis.
- Osteogenesis imperfecta can have similar effects on the ossicles (and histologically is indistinguishable) but its typical features, such as the presence of blue sclerae or other bony abnormalities, may help to detect the underlying condition.
- Audiometry is the primary investigation of choice. Bone and air conduction must be tested and typically reveal a purely conductive, predominantly low-tone loss.
- If the cochlea is also involved there will be mixed sensorineural/conductive loss. It is difficult to distinguish the sensorineural loss of otosclerosis from other causes of sensorineural hearing loss.
- Audiogram patterns such as Carhart's notch (a drop in bone conduction thresholds of 20-30 dB, most pronounced at 2000 Hz) and excessive sensorineural loss (beyond any likely presbycusis) may help to discriminate.
- Tympanometry may show a stiffness curve, indicating low compliance of the tympanic membrane and ossicular chain.
- Fine-slice CT scanning may be used to demonstrate new abnormal bone deposition in the temporal bone via the so-called 'halo' sign, which appears to be a useful diagnostic adjunct in this condition.
- Hearing loss can be ameliorated through the correct use of bilateral hearing aids.
- Sodium fluoride 20-120 mg daily has been used as a medical therapy, via its effect on bone metabolism, forming fluorapatite complexes. Evidence is of low quality only.[11, 12]
- Bisphosphonate treatment has been used as an alternative in those unable to tolerate fluoride therapy. Recent studies show promising results for this treatment.
Surgical therapy has advanced significantly over the period of a few decades and this is now an effective and popular form of treatment. Stapedectomy (extraction of the footplate) or stapedotomy (a small hole made in the stapes footplate) aims to improve the circulation of fluid within the cochlear canal. They are short procedures that can be done as day cases. The use of minimally invasive techniques, sometimes involving lasers, has been developed. Up to 95% of patients experience elimination of their conductive hearing loss (defined as <10 dB air-bone gap on audiometry) with little to choose between the two procedures. It also increases quality of life of these patients by improving their social life and delaying the need for a hearing aid.Benefits are long-lasting.However, surgery may not completely obviate the need to use a hearing aid.
Revision surgery (where there has been previous surgical failure or with progressive disease) is much less successful.
- If the condition is not treated, it leads to significant hearing loss of about 50-60 dB but total deafness is uncommon.
- Stapedectomy/stapedotomy can cause total unilateral sensorineural hearing loss in about 1-2% of cases. The exact cause for this is uncertain and not connected with any particular surgical errors. Unfortunately, this rarely improves or responds to amplification.
- Facial nerve injury occurs in about 1 in 1,000.
- Perforations of the eardrum may occur, but are usually easy to repair and they heal well.
- Disturbance of taste sensation, due to intraoperative manipulation of the chorda tympani, is a possible complication, but usually transient.
- For a minority, tinnitus may arise de novo, or worsen.
Otosclerosis treated surgically has a good prognosis in the vast majority of cases. The rate of hearing deterioration with time after stapedotomy does not exceed that due to presbyacusis.
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Further reading & references
- Genetic Heterogeneity in Otosclerosis; Online Mendelian Inheritance in Man (OMIM)
- Isaacson J and Vora N; American Family Physician Review: Differential Diagnosis and Treatment of Hearing Loss. Am Fam Phys 2003 Sep 15
- Hannan S et al; Tinnitus. BMJ 2005 29 Jan 330:237. Succinct overview of primary care approach
- Uppal S, Bajaj Y, Rustom I, et al; Otosclerosis 1: the aetiopathogenesis of otosclerosis. Int J Clin Pract. 2009 Oct 63(10):1526-30.
- Schrauwen I, Van Camp G; The etiology of otosclerosis: a combination of genes and environment. Laryngoscope. 2010 Jun 120(6):1195-202.
- Thys M, Van Camp G; Genetics of otosclerosis. Otol Neurotol. 2009 Dec 30(8):1021-32.
- Karosi T, Konya J, Petko M, et al; Two subgroups of stapes fixation: otosclerosis and pseudo-otosclerosis. Laryngoscope. 2005 Nov 115(11):1968-73.
- Declau F, van Spaendonck M, Timmermans JP, et al; Prevalence of histologic otosclerosis: an unbiased temporal bone study in Caucasians. Adv Otorhinolaryngol. 2007 65:6-16.
- Arnold W, Busch R, Arnold A, et al; The influence of measles vaccination on the incidence of otosclerosis in Germany. Eur Arch Otorhinolaryngol. 2007 Jul 264(7):741-8. Epub 2007 Feb 13.
- Niedermeyer HP, Arnold W; Otosclerosis and measles virus - association or causation? ORL J Otorhinolaryngol Relat Spec. 2008 70(1):63-9
- Eza-Nunez P, Manrique-Rodriguez M, Perez-Fernandez N; Otosclerosis among patients with dizziness. Rev Laryngol Otol Rhinol (Bord). 2010 131(3):199-206.
- Vicente Ade O, Yamashita HK, Albernaz PL, et al; Computed tomography in the diagnosis of otosclerosis. Otolaryngol Head Neck Surg. 2006 Apr 134(4):685-92.
- Uppal S, Bajaj Y, Coatesworth AP; Otosclerosis 2: the medical management of otosclerosis. Int J Clin Pract. 2010 Jan 64(2):256-65.
- Liktor B, Szekanecz Z, Batta TJ, et al; Perspectives of pharmacological treatment in otosclerosis. Eur Arch Otorhinolaryngol. 2013 Mar 270(3):793-804. doi: 10.1007/s00405-012-2126-0. Epub 2012 Jul 29.
- Cruise AS, Singh A, Quiney RE; Sodium fluoride in otosclerosis treatment: review. J Laryngol Otol. 2010 Jun 124(6):583-6. Epub 2010 Feb 18.
- Quesnel AM, Seton M, Merchant SN, et al; Third-generation bisphosphonates for treatment of sensorineural hearing loss in otosclerosis. Otol Neurotol. 2012 Oct 33(8):1308-14. doi: 10.1097/MAO.0b013e318268d1b3.
- Bajaj Y, Uppal S, Bhatti I, et al; Otosclerosis 3: the surgical management of otosclerosis. Int J Clin Pract. 2010 Mar 64(4):505-10.
- Karhuketo TS, Lundmark J, Vanhatalo J, et al; Stapes surgery: a 32-year follow-up. ORL J Otorhinolaryngol Relat Spec. 2007 69(5):322-6. Epub 2007 Aug 23.
- Bernardo MT, Dias J, Ribeiro D, et al; Long term outcome of otosclerosis surgery. Braz J Otorhinolaryngol. 2012 Jul-Aug 78(4):115-9.
- Redfors YD, Hellgren J, Moller C; Hearing-aid use and benefit: a long-term follow-up in patients undergoing surgery for otosclerosis. Int J Audiol. 2013 Mar 52(3):194-9. doi: 10.3109/14992027.2012.754957. Epub 2013 Jan 22.
- Mahafza T, Al-Layla A, Tawalbeh M, et al; Surgical Treatment of Otosclerosis: Eight years' Experience at the Jordan University Hospital. Iran J Otorhinolaryngol. 2013 Sep 25(73):233-8.
- Vincent R, Sperling NM, Oates J, et al; Surgical findings and long-term hearing results in 3,050 stapedotomies for primary otosclerosis: a prospective study with the otology-neurotology database. Otol Neurotol. 2006 Dec 27(8 Suppl 2):S25-47.
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