Differential_Diagnosis_of_Otosclerosis

Differential Diagnosis: Case Scenario 1 Differential diagnosis enables a systematic, scientific approach towards patient management, enabling the audiologist to: - Quickly eliminate conditions, which may be life threatening - Gain insight in to prognosis and plan effective management - Provide information useful to future differential diagnoses - Enable the patient to understand their condition and develop coping strategies Audiological testing Otoscopy: In this patient otoscopy is reported as normal, indicating that the pinna and ear canal are clear and normal and the tympanic membrane (TM) is of normal colour- translucent pearly grey, normal malleus orientation, no perforation/surgical legacy, bright cone of light, no retraction pockets or evidence of fluid accumulation. Tuning Fork Tests: A positive Rinne result requires AC to be reported as louder than BC. A negative Rinne result requires BC to be reported as louder than AC, indicative of conductive hearing loss (CHL). Where AC and BC are equally depreciated (e.g. in sensorineural (SNHL)/mixed (MHL) hearing loss) a false positive result is possible. The Weber test enables the audiologist to see whether one ear is hearing better than the other. A person with CHL or SNHL would report localisation in the affected or unaffected ear respectively. A patient with a symmetric hearing loss may report central localisation and therefore an equivocal result. In this patient a negative Rinne is reported bilaterally suggesting bilateral CHL. The Weber provided “equivocal” results, thus providing initial support for a bilateral pathology. Pure Tone Audiometry (PTA) In PTA the AC threshold provides information on the sensitivity of overall hearing function. The BC threshold provides a measure of integrity of cochlea function only (reflecting SNHL). Any air bone gap (ABG) provides a measure of the magnitude of CHL. PTA for this patient shows a “mild” CHL resulting from abnormalities within the ME (Katz 1994). BC is generally normal thus providing no indication of SNHL. A notch in BC is reported at 2000 Hz reducing the ABG to 15dB. This suggests a 15dB SNHL at this frequency. Tympanometry Tympanometry tests the integrity of the ME through measurement of immitance on presentation of a pure tone and varying air pressure via a probe tip. This patient’s Tympanometry results show low bilateral compliance (Type As curve, as categorised by Jerger in Katz 1994), indicating a restriction of movement of the TM due to TM or ossicular dysfunction. Type A response supports otoscopic findings that the TM is intact (Katz 1994). Acoustic Reflexes In ARs for a normally hearing individual, sound input from a tone probe is perceived by the auditory (VIIIth) nerve resulting in involuntary output from the facial (VIIth) nerve as the stapedial reflex. ARs can be tested ipsilaterally or contralaterally. Abnormal reflexes can indicate problems with sound transmission through ME or retrocochlear reflex pathways. However in cases of bilateral CHL ARs are often completely absent ipsilaterally and contralaterally due the following principle described by Katz (1994): Probe ear principle- a conductive loss greater than 5dB in the probe ear will result in absent reflexes. Consequently, in a bilateral CHL such as this patient presents all ARs will be recorded as absent in both ears as every test involves stimulating a pathologic ear. Documented test results are in concurrence with these principles. It is essential to note here that retrocochlear disorders often result in absent ARs (Katz 1994). Differential diagnosis Conclusions for this patient far are: - CHL with potential SNHL at 2000Hz - Restriction of TM movement (potential dysfunction in TM/ossicular mobility) - Potential retrocochlear pathology A discussion of potential diagnoses on the basis of this information follows. Retrocochlear Pathology Description: Retrocochlear lesions refer to pathologies between the VIIIth cranial nerve and the cerebello-pontine angle in the brainstem e.g. acoustic neuroma (Gelfland 1996). They present a risk to central auditory and nervous system function. Support for differential diagnosis: - Absent/elevated ARs - Impaired speech perception - Commonly unilateral - Potentially normal PTA - Vertigo - Tinnitus Probability of correct diagnosis for patient: Retrocochlear leisions are extremely rare bilaterally (1 in 33 000) (Evans et al. 1992), although a combined hearing loss must be considered. It seems unlikely that this patient has retrocochlear pathology but it is essential to definitively rule this out of diagnosis. Live voice testing for this patient produced scores which would be expected from her thresholds. In retrocochlear pathology lower scores would be expected due to its effect on neural synchrony (Canty 1978). Absent ARs mean we cannot rule this diagnosis out at this stage. Further testing: - Further speech testing at higher levels may help to confirm conductive pathology - MRI scan for tumour detection. This requires ENT referral. Cholesteatoma Description: Cholesteatoma is a build up of highly infectious keratin in the ME cavity which may erode the ossicles/otic capsule and spread infection to the brain. Usually this occurs where the TM is perforated (“open”) but rare cases have been reported where a cholesteatoma has developed behind an intact TM (“closed”) (Katz 1994). Support for differential diagnosis: - Ottorhea - Otalgia - History of OME - Tinnitus - CHL - Vertigo - TM retraction pockets - Perforated TM (existing or history) - Pearlescent polyps Probability of correct diagnosis for patient: Cholesteatoma can be ruled out of diagnosis as the patient has no history of OME or ear problems and a normal TM and ear canal appearance on otoscopy. Tympanosclerosis Description: Tympanosclerosis results from the deposition of calcium/phosphate crystals in the process of healing following chronic OM. Tympanosclerosis may result in ossicular fixation (Gibb & Pang 1994). Support for differential diagnosis: - Prolonged history of OME - CHL - Perforated eardrum (80% of cases) (Lalwali 2004) - Visible white plaques on TM - White colouring on TM - Type As tympanogram Probability of correct diagnosis for patient: No history of infection or ear pain is reported and TM is normal. Ossicular fixation in tympanosclerosis could produce the same audiological test results as otosclerosis, including a Carhart’s notch in PTA (Bremond et al 1985). Sheehy & House (1960) report that in 2/3 cases a diagnosis of closed tympanosclerosis is not made until the ME is opened surgically with a view to treating otosclerosis. Further testing: A high resolution CT scan would be useful in investigating the extent and nature of any sclerosis and where in the ME cavity it is located. This would require referral to ENT. Use of Siegel’s speculum could provide more information on TM mobility. Otitis Media with Effusion (OME) Description: OME occurs when the Eustachian tube becomes blocked and fluid secretions are prevented from draining to the throat. This fluid builds up in the ME cavity and provides a breeding ground for bacteria. Support for differential diagnosis: - CHL - History of ear infection - Otalgia - Visible fluid behind eardrum - TM opaque, dull/distorted cone of light - Flat/shallow (type As/B) tympanogram - Inflammation - TM retraction (adhesive OME) - Probability of correct diagnosis for patient: A diagnosis of OM for this patient is unlikely as no history of ear infection/otalgia is reported in history (she is fit and healthy and takes no medication). The TM is also of normal healthy appearance. Ossicular discontinuity Description: Ossicular discontinuity refers to a break in the ossicular chain. Support for differential diagnosis: - History of head trauma - Flaccid TM - Type Ad tympanogram (high compliance) Probability of correct diagnosis for patient: The patient reports no history of head trauma and tymapnometry shows lowered TM compliance. TM is of normal appearance therefore this diagnosis can be eliminated from consideration. Noise Induced Hearing Loss (NIHL) Description: Hair cell damage in the inner ear due to prolonged exposure to high noise levels or sudden one time exposure to a dangerously high sound stimulus. Support for differential diagnosis: - History of extended periods of time spent in high level noise environments - Report of exposure to sudden loud sound e.g. gun shot - Notch in audiogram 4-6 kHz - SNHL - Tinnitus Probability of correct diagnosis for patient: This patient worked in a laundrette for 10 years-an environment has a potentially high constant noise level. It is possible that the dip in BC at 2000Hz is NIHL, although more commonly an NIHL audiogram notch occurs between 4-6 kHz (McBride & Williams 2001). Washing machines typically produce higher frequency sound levels so although possible, NIHL at this specific frequency seems unlikely. Diffuse bone disorders Description: Paget’s disease is a chronic bone disorder. Hearing loss occurs when disease reaches the skull (more specifically the otic capsule) (Mills & Singer 1976, Jenkins 1923). Osteogenesis Imperfecta is an autosomal dominant disease causing brittle bones (Byers et al 1992). Support for differential diagnosis: - Involvement of the bone disorder in other parts of the body e.g. fracture - Generalised bone pain - CHL - Onset over 40 years of age (Paget’s) - Family history (osteogenesis) Probability of correct diagnosis for patient: The patient is reported as fit and healthy. Therefore we can assume she does not have any generalised skeletal disorder. Otosclerosis Description: Otosclerosis is a disease of the otic capsule, caused by abnormal bone homeostasis (Van Den Bogaert et al 2003, Lalwali 2004), affecting 4 in 1000 of the adult population and onset peaking in the 3/4th decade of life (Morrison 1970, Katz 1994, Lalwali 2004) . CHL occurs through fixation of the stapes footplate in the oval window, impeding sound transmission from the ME to the cochlea and is commonly bilateral (Katz 1994). SNHL develops if and when the disease spreads to the cochlea (Morrison 1970, Lalwali 2004). A specific audiometric characteristic of otosclerosis is Carhart’s notch- an increase in BC thresholds of around 15dBHL peaking at 2000Hz due to the mechanical effects of stapedial fixation (Carhart, 1950, 1971). Tonndorf (1971) reports that the frequency of Carhart’s notch relates to the resonant frequency of the ossicular chain for BC signals (around 2,000 Hz in humans) and therefore is not a true reflection of cochlea function as it is corrected following stapedectomy surgery (Katz 1994). Support for differential diagnosis: - Positive family history - Report of gradually progressive hearing loss (commonly bilateral) - Early onset (detected by the 3rd/4th decade of life) - CHL - Paracusis - Carhart’s notch on audiogram - Report of worsening of hearing sensitivity during pregnancy/hormone treatment - Greater apparent prevalence in females - Shwartze sign (pinkish tinge to TM in cochlear otosclerosis) - Tinnitus - History of measles virus (in sporadic cases) Probability of correct diagnosis for patient: The patient exhibits a majority of the symptoms associated with otosclerosis. The patient is female, within the 4th decade of life and reports a gradual progressive bilateral hearing loss with tinnitus. She reports evidence of early onset hearing loss in family history (her aunt). Paracusis of Willish (the ability to hear better in background noise) is widely documented in the early stages of otosclerosis (e.g. Lalwali 2004) and is reported by this patient. This patient’s audiogram shows a Carhart’s notch at 2000Hz and no other evidence of SNHL (therefore, as would be expected, no Schwartze sign is visible). Further testing: It would be useful to ask the patient if she could find out more about her aunt’s hearing loss and how she was treated for it. Findings of otosclerosis would add weight to the current diagnosis. A high resolution CT scan (sensitive to 90% of cases) scan may confirm suspicions of otosclerosis and help to rule out a closed tympanosclerosis from differential diagnosis (Vicenta et al 2006, Berrettini et al. 2002). At this stage further investigation from the ENT department is required to confirm diagnosis and rule out any retrocochlear pathology i.e. MRI scan. Patient information is most consistent with this diagnosis of otosclerosis. Therefore on the basis of given information I conclude that this is the most likely scenario at this stage of differential diagnosis (although retrocochlear pathology and tympanosclerosis still need to be eliminated). ENT referral is essential for management. Patient Management There are 3 main treatment options available for suspected otosclerosis: 1. Observation The patient should always be given the options and prognosis for leaving disease to its natural progression. The audiologist must make sure the patient is aware of prognosis of all management options. 2. Surgery Stapedectomy involves removal of the fixed stapes and replacement with prosthesis (Morrison 1970). Stapedial surgery demonstrates successful closure of ABG in 92% of patients (Morisson 1970). Patients with a preoperative AC of less than 50 dB have demonstrated normal hearing thresholds postoperatively. In patients with moderate hearing loss, hearing aid fittings were much more successful postoperatively (Luntz, M., Yehudai, N. & Most, T. 2009, Morisson 1970). Due to the young age of the patient and her mild 30dB surgery may provide an excellent solution to her hearing loss. She must be informed however that there is a chance of postoperative SNHL and that hearing may continue to deteriorate by 0.6-1.2dB per year as disease will not be completely cured (Vincent, R., Sperling,N. M., Oates, J & Jindal, M. 2006). 3. Hearing Aids Patients exhibiting CHL with effective speech discrimination are good candidates for amplification from a post-aural or bone anchored hearing aids (Burell et al 1996). The benefit of hearing aids being that the risks of surgery are eliminated. Additional Management Considerations Referral to Hearing Therapy may be useful in helping the patient come to terms with her disability by assisting development of coping mechanisms e.g. lip reading and communication strategies. Information on assistive devices (the patient reports difficulty in using the TV etc.), should also be given alongside details of government schemes such as Access to Work to assist the patient in maintaining her independence. The patient should be counselled as to the progressive nature/prognosis of the disease in all cases. References Berrettini, (2002). Single Photon Emission Computed Tomography in Otosclerosis: Diagnostic Accuracy and Correlation with Age, Sex, and Sensorineural Involvement. Otology & neurotology [1531-7129] vol:23 iss:4 pg:431 Bremond G, Bonnaud G, Magnan J (1985). La tympanosclerose. Encycl Med Chir Burrell, S. P., Cooper, H. C. and Proops, D. W. (1996), The bone anchored hearing aid—The third option for otosclerosis. 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