01OverviewDefinition, clinical context and the essential points that orientate the chapter.
The purpose of classifying hearing loss is to identify what may be treatable and what further assessment is needed. Airborne sound must pass through the canal, move the tympanic membrane and ossicles, and reach the cochlea, where mechanical energy is converted into neural activity. Failure along the visible conductive pathway can reduce the sound reaching an otherwise functioning cochlea. Cochlear or auditory neural injury can impair hearing even when the canal and drum look normal. Both mechanisms can occur in the same ear.
The patient rarely describes these mechanisms directly. Fullness may accompany wax, middle-ear fluid or sudden sensorineural loss. Difficulty following speech in a restaurant can arise from high-frequency hearing impairment even when conversation in a quiet room appears manageable. Ask what changed, how quickly it changed, whether it affects one ear, and which activities are now difficult. A useful chronology identifies the last time hearing was normal, the interval over which it worsened and the delay before presentation; these are distinct measurements.
A conductive label is strongest when the clinical findings and hearing measurements agree. An obstructing wax plug or fluid behind the membrane is relevant, but incidental wax does not necessarily explain a severe deficit. After safe treatment, residual hearing difficulty still needs assessment. Conversely, an intact normal-looking membrane does not rule out ossicular fixation or a less visible middle-ear abnormality. Avoid treating the otoscopic image as a complete physiological hearing test.
Audiometry separates air and bone thresholds at individual frequencies. Lower numerical thresholds represent better sensitivity, while higher values mean a louder stimulus was needed. Bone-conducted vibration can reach both cochleae, so an unmasked response may belong to the better ear. The audiologist uses masking when indicated to obtain valid ear-specific information. Classification must therefore use the final interpreted audiogram, including reliability and masking notes, rather than reading any apparently normal bone line as proof that the symptomatic cochlea is normal.
Key points
- Conductive loss reduces sound transfer through the outer or middle ear; sensorineural loss affects cochlear or neural function.
- Air-conduction thresholds test the entire pathway, while bone conduction helps assess function beyond the outer and middle ear.
- A conductive component creates an air-bone gap when reliable ear-specific thresholds have been established.
- Mixed loss combines elevated bone-conduction thresholds with an additional conductive deficit.
- Rinne positive means air conduction is perceived better than bone conduction; it does not mean hearing is normal.
- Use onset, symmetry, examination and functional needs together; classification alone does not determine referral urgency or rehabilitation.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Obstruction or middle-ear dysfunction
Wax, a foreign body, canal inflammation, middle-ear fluid, perforation and ossicular abnormalities can limit sound transmission. Their visibility and reversibility vary, so history, examination and hearing measurements need to be interpreted together.
Cochlear or auditory neural injury
Age-related change, noise, ototoxic exposure, sudden idiopathic loss and other inner-ear or neural disorders can impair hearing beyond the conductive pathway. Asymmetry or associated neurological findings may require investigation for a focal lesion.
Coexisting mechanisms
An adult with established cochlear impairment can also develop wax, fluid or another conductive problem. Treating one component may improve hearing substantially while leaving an important residual sensorineural deficit requiring rehabilitation.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Attenuation before the cochlea
A conductive lesion reduces the efficiency with which air-conducted energy reaches the inner ear. Bone-conducted stimulation partly bypasses this route, producing better bone than air thresholds when the measurements are reliable and appropriately masked.
- 2Reduced sensory or neural sensitivity
Cochlear and auditory neural dysfunction can elevate both air- and bone-conduction thresholds without a substantial gap. Frequency-specific damage may reduce speech clarity and listening performance even when some tones remain relatively easy to detect.
- 3Additional transmission and sensory deficits
Mixed hearing loss combines impaired cochlear or neural sensitivity with further attenuation in the outer or middle ear. The audiogram therefore shows elevated bone thresholds and poorer air thresholds at frequencies with a conductive component.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Ask whether loss was abrupt, rapidly progressive over days to months, fluctuating or slowly progressive over years. Clarify whether one ear is worse and whether prior hearing was already impaired. A patient who notices loss on waking may still have a sudden presentation despite uncertainty about its exact overnight onset.
Canal blockage, discharge, recent respiratory illness, a perforation or a history of middle-ear surgery may support a transmission problem. These findings do not exclude an additional cochlear deficit, particularly when the magnitude of hearing change seems disproportionate.
Noise exposure, ototoxic treatment, gradual bilateral high-frequency difficulty, sudden unexplained loss or hearing asymmetry with an unremarkable drum can suggest cochlear or neural disease. Symptoms alone cannot reliably determine the lesion or the full degree of impairment.
Ask about tinnitus, vertigo, otalgia, headache, facial symptoms and neurological change. Examine the ears and cranial nerves where indicated, and check that apparent inattention or misunderstanding is not simply an inaccessible spoken conversation.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
History, otoscopy and communication assessmentFirst step - Why
- Identify obvious causes, urgent patterns and the person's functional priorities.
- Interpretation and limitations
- NICE advises excluding impacted wax and acute infections before routine audiological assessment, but recent unexplained sudden loss follows an immediate referral route. Describe any uncertainty about whether an observed lesion accounts for the deficit.
- 02
Combined Weber and Rinne testing - Why
- Provide a provisional bedside indication of a conductive component or asymmetry.
- Interpretation and limitations
- Use a 512 Hz fork with correct technique and interpret both tests together. Symmetrical sensorineural loss can produce a central Weber and bilateral positive Rinne tests, so apparently conventional results cannot exclude significant impairment.
- 03
Pure-tone air and bone audiometry - Why
- Quantify frequency-specific hearing sensitivity and distinguish transmission from sensory components.
- Interpretation and limitations
- Use masked thresholds when required and inspect reliability comments. A raised air line with preserved bone sensitivity supports conductive loss; elevation of both without a meaningful gap suggests sensorineural loss; elevated bone with an additional gap supports mixed loss.
- 04
Tympanometry and directed MRI - Why
- Investigate middle-ear mechanics or possible focal neural pathology when indicated.
- Interpretation and limitations
- Tympanometry provides mechanical information rather than a cochlear hearing threshold. NICE recommends offering MRI of the internal auditory meati for localising signs suggesting a vestibular schwannoma or cerebellopontine-angle lesion regardless of thresholds; without localising signs, the specified asymmetry criterion supports considering MRI.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
An isolated conductive presentation
A clear air-bone gap with otherwise preserved bone sensitivity supports a conductive mechanism. Its cause still needs identification, and an apparently explanatory otoscopic finding should be checked against the severity and course of the loss.
An isolated sensorineural presentation
Comparable elevation of air and valid bone thresholds suggests a predominantly sensorineural deficit. Sudden onset, asymmetry, tinnitus or neurological findings influence investigation and urgency beyond the audiometric classification itself.
Testing or communication limitations
Inconsistent instructions, environmental noise, transducer problems or cross-hearing can distort an audiogram. Repeat or adapted testing may be needed before assigning a physiological explanation, without postponing urgent assessment when the history is concerning.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Sudden or rapidly progressive lossApply the correct referral clockFirst stepThe history suggests recent onset or progression without an adequate external or middle-ear cause.+
- 1Refer a loss developing within three days and occurring within the last 30 days immediately, aiming for assessment within 24 hours.
- 2For sudden loss beginning more than 30 days ago, or worsening over four to 90 days, arrange urgent ENT or audiovestibular assessment within two weeks.
- 3Use emergency neurological assessment when the associated findings suggest stroke or another acute central disorder, and communicate the separate onset and presentation dates.
02A potentially treatable conductive componentTreat the demonstrated cause and check the resultExamination and hearing findings support obstruction or a middle-ear disorder.+
- 1Select treatment or referral from the actual lesion, with particular caution around a perforation, an operated ear or persistent discharge.
- 2Reassess the hearing complaint after the conductive problem is addressed, rather than assuming that clearance of wax or infection restores all auditory function.
- 3Arrange audiology or ENT assessment if hearing remains impaired, the membrane remains abnormal or the course does not fit the proposed explanation.
03Persistent sensorineural asymmetryInvestigate risk while planning rehabilitationAudiometry demonstrates asymmetry not explained by an acute external or middle-ear process.+
- 1Look for localising signs and symptoms, since these can justify offering internal-auditory-meatus MRI independently of a numerical threshold difference.
- 2Without localising signs, consider MRI when the interaural difference is at least 15 dB at two adjacent frequencies among 0.5, 1, 2, 4 and 8 kHz.
- 3Explain the reason for diagnostic referral and discuss hearing support in parallel, taking account of communication goals and the patient's preferences.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Delayed treatment of acute cochlear loss
Attributing abrupt loss to a blocked-ear sensation or small amount of wax can delay time-sensitive assessment. A normal canal or incomplete conductive explanation should increase attention to the history rather than encourage prolonged observation.
Missed focal pathology
Persistent asymmetric sensorineural thresholds or localising cranial nerve findings may indicate a retrocochlear lesion. Hearing rehabilitation can proceed alongside appropriate investigation, but should not become a reason to omit it.
Loss of communication and participation
Untreated hearing difficulty can restrict work, relationships and recognition of warning sounds. Its practical impact depends on listening demands and support as well as pure-tone thresholds, making individual goals essential to management.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Compare the patient's reported hearing and functional goals with the measured thresholds after any treatment.
- Track whether unilateral loss, tinnitus, vertigo or neurological findings have changed while diagnostic assessment is pending.
- Ensure any planned MRI, ENT appointment or repeat audiogram has a named clinical purpose and a route for following up the result.
- Review communication support at home and work, including access to alerts, telephone use and whether the person can hear clinical advice.
- Provide a clear route to urgent reassessment if hearing changes abruptly again, even in someone already using hearing aids.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
A mixed loss is not a failed classification
Finding both components is clinically useful because the conductive element may be reversible while the sensory element needs ongoing support. Explain anticipated partial benefit from treatment without promising that correcting the visible lesion will restore normal hearing.
The better cochlea can disguise asymmetry
Bone-conducted sound spreads through the skull. Without appropriate masking, the response attributed to the poorer ear may be generated by the opposite cochlea. A masked audiogram can therefore change the apparent mechanism as well as the severity.
Speech difficulty may exceed the chart impression
Pure-tone thresholds do not reproduce competing talkers, reverberation or rapid conversation. Ask about these settings and discuss appropriate assessment or hearing support when daily difficulty remains substantial despite relatively preserved thresholds at some frequencies.
A classification is not a complete diagnosis
Sensorineural describes the affected part of the pathway, not whether the cause is age-related, inflammatory, vascular, toxic or neoplastic. Likewise conductive loss does not identify the particular canal, membrane or ossicular lesion. The next step follows the unresolved clinical question.
11Common pitfallsFrequent interpretation and management errors.
- 01
Equating a positive Rinne result with normal hearing rather than understanding its air-versus-bone comparison.
- 02
Using unmasked bone thresholds to reassure about a profoundly impaired ear without considering cross-hearing.
- 03
Explaining a large sudden deficit by incidental non-occluding wax and arranging only a routine cleaning appointment.
- 04
Treating asymmetric hearing as ordinary ageing without checking diagnostic referral and MRI criteria.
- 05
Confusing the time over which hearing deteriorated with the time elapsed before the patient sought care.