Tinnitus, derived from the Latin word "tinnere" meaning a ringing-like sound, refers to a subjective perception of noise within the ear or head in the absence of external sound sources or stimuli. It is one of the most common symptoms encountered in otologic clinics and is often described by patients as ringing, chirping, hissing, or other types of noise. Tinnitus has a relatively high incidence rate, increasing with age. Approximately 17% of the general population experience tinnitus to varying degrees, with an even higher prevalence among the elderly. The impact of tinnitus varies; mild cases may be negligible, while severe cases can lead to significant psychological and mental health disturbances.
Etiology and Classification
There are several methods to classify tinnitus, the most common of which are as follows:
Subjective Tinnitus and Objective Tinnitus
Based on whether others can perceive the tinnitus, it is categorized into subjective and objective tinnitus. Subjective tinnitus is sound perceived only by the patient, while objective tinnitus can be heard by both the patient and others. Subjective tinnitus accounts for the vast majority of clinical cases.
Physiological Tinnitus and Pathological Tinnitus
Normal individuals may experience tinnitus in a quiet environment or hear vascular pulsations during activity or in a lateral-lying position, which is referred to as physiological tinnitus (also known as bodily sounds). Tinnitus caused by diseases such as inflammation, tumors, malformations, or trauma is classified as pathological tinnitus.
Classification by Cause
Causes of tinnitus include inflammation, tumors, trauma, malformations, allergies, metabolic diseases, immune disorders, ototoxic drug toxicity, aging, noise exposure, and psychological or mental factors. Common associated conditions include otitis media, otosclerosis, thyroid dysfunction, cervical spondylosis, multiple sclerosis, Paget’s disease, iodine or zinc deficiency, anemia, migraines, hypertension, hyperlipidemia, kidney diseases, and autoimmune disorders. Additionally, a type of subjective tinnitus of unknown cause, known as idiopathic tinnitus, exists. In such cases, no significant abnormalities are found using current diagnostic tools (including physical examination of the ear and body, audiological tests, imaging studies, and laboratory tests), or no clear causal relationship is identified between abnormal findings and the tinnitus.
Classification by Site of Tinnitus Origin
Otic Tinnitus
Tinnitus originates within the auditory system, including the external ear, middle ear, inner ear, auditory nerve, brainstem, and auditory cortex:
- External Ear and Middle Ear: Conditions affecting these areas, such as external or middle ear disorders, reduce the masking effect of ambient noise on physiological bodily sounds. This decreased masking effect may amplify internal physiological noise, resulting in tinnitus. In addition, conditions such as glomus jugulare tumors, otosclerosis, or middle ear effusion can cause pulsatile tinnitus synchronized with the heartbeat rhythm.
- Cochlear Disorders: Though the exact mechanism remains unclear, many researchers attribute tinnitus to spontaneous discharge activity in abnormal regions. Damage to hair cells in the cochlea leads to prolonged depolarization, eliciting neuronal excitation and abnormal signals.
- Retrocochlear Disorders: These typically occur in the internal auditory canal and cerebellopontine angle, closely associated with the auditory nerve. Lesions in these regions (e.g., vestibular schwannomas or vascular anomalies) may compress the auditory nerve, causing abnormal nerve impulses and tinnitus.
- Auditory Central Disorders: Lesions in the brainstem or auditory cortex, including tumors, vascular abnormalities, inflammation, and multiple sclerosis, that involve the cochlear nucleus, efferent fibers, or afferent fibers of the auditory system can also lead to tinnitus.
Non-Otic Tinnitus
Tinnitus originates outside the auditory system, often referred to as bodily sounds:
- Vascular-Origin Tinnitus: Often caused by intracranial or extracranial vascular anomalies such as sigmoid sinus diverticulum, arteriovenous fistulas, aneurysms, or arteriovenous malformations, resulting in pulsatile tinnitus synchronized with heartbeat rhythms.
- Myogenic Tinnitus: Palatal myoclonus is a common cause of objective tinnitus, described as irregular clicking sounds that synchronize with spasmodic contractions of the soft palate. Additionally, spasmodic contractions of middle ear muscles, including the stapedius or tensor tympani, can result in rhythmic clicking sounds.
- Eustachian Tube Abnormalities: Patients with patulous eustachian tube may perceive tinnitus synchronized with their breathing rhythms.
- Temporomandibular Joint Disorders: Temporomandibular joint arthritis or imbalance in dental occlusion can cause clicking-like tinnitus heard near the external auditory canal during chewing or mouth movements.
Classification by Presence or Absence of Organic Lesions
Tinnitus with no organic lesions is referred to as functional or psychogenic tinnitus. For example, individuals with hysteria tendencies who endure significant psychological trauma may develop psychogenic or hysterical tinnitus, as seen with auditory hallucinations triggered by specific causes. Another scenario involves cases where patients subjectively exaggerate or feign descriptions of tinnitus symptoms.
Pathogenesis
In cases of objective tinnitus or tinnitus secondary to other diseases, the underlying cause of the tinnitus is often identifiable. However, the mechanisms of idiopathic subjective tinnitus remain unclear. Current research is limited to theoretical assumptions and lacks robust scientific data or clinical evidence for support. Historically, because tinnitus was frequently observed in patients with cochlear lesions, research primarily focused on cochlear function. However, numerous experimental and clinical studies have found that tinnitus can persist even after the auditory nerve is severed, and in some cases, tinnitus has been observed to arise following auditory nerve section. In 1990, Jastreboff proposed that tinnitus originates during the auditory central processing of weak signals from the auditory nerve endings and is closely associated with the autonomic nervous system and limbic system.
The prevailing viewpoint is that tinnitus is a clinical condition primarily involving peripheral and central mechanisms with multifactorial contributions. Abnormal neural activity at various levels participates in the generation of tinnitus. Two possible mechanisms have been proposed:
Synchronized Discharges Between Adjacent Neurons
Affected neurons and excitatory neurons exhibit synchronized discharges due to pathological influences. This hypothesis helps explain the mechanism of tinnitus associated with auditory neuropathy.
Excessive Influx of Cations into Hair Cells
Cochlear hair cells exhibit spontaneous and excessive influx of potassium (K+) and calcium (Ca2+) ions, causing a synchronized release of neurotransmitters from all synapses. This hypothesis provides an explanation for the mechanisms underlying noise-induced and drug-induced tinnitus.
Examinations
Physical Examinations
General physical examinations are conducted to assess the patient's overall condition and investigate any systemic diseases that may be present. Neurological examinations are performed to evaluate and rule out central nervous system or peripheral nervous system disorders potentially associated with tinnitus. Otolaryngological examinations should include routine assessments as well as specific attention to the cervical region (including the thyroid) and temporomandibular joint function. For cases involving pulsatile tinnitus, auscultation around the neck and ear regions may be performed, along with compression of cervical blood vessels to analyze the rhythm of the tinnitus and the effects of pressure on the carotid arteries and veins.
Supplementary Examinations
Hearing Function Testing
For patients with unilateral tinnitus, persistent tinnitus lasting 6 months or more, or tinnitus accompanied by hearing impairment, a comprehensive audiological evaluation may include pure-tone audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAE).
Vestibular Function Testing
Assessments may include tests for balance function, coordination, and oculomotor evaluations.
Tinnitus-Specific Testing
Specific tinnitus tests may involve pitch or frequency matching, volume matching, masking ability testing, and residual inhibition testing.
Imaging Studies
Temporal bone CT scans can directly visualize sigmoid sinus diverticula contributing to pulsatile tinnitus and detect other middle ear abnormalities. MRI of the internal auditory canal may help rule out tumors or other structural lesions. For suspected vascular abnormalities causing pulsatile tinnitus, carotid artery color Doppler ultrasound, cerebral vascular CT angiography (CTA), and, if necessary, digital subtraction angiography may be performed to determine the underlying cause.
Other Examinations
Based on the patient's medical history, further investigations of systemic diseases could include specific evaluations such as thyroid function tests, blood glucose, urine glucose, blood pressure, lipid profiles, and immunological tests.
Diagnosis
Tinnitus is a common symptom in otology with a wide range of causes, including ear-related diseases and systemic conditions. Many factors can trigger or influence tinnitus, and it often interacts with psychological and emotional issues, forming a vicious cycle. Diagnosing tinnitus can therefore be challenging, and in some cases, the underlying cause cannot be identified even after thorough investigations.
The diagnostic process involves identifying the location, underlying cause, and severity of tinnitus. This requires determining the site of occurrence, evaluating potential etiologies, and grading the intensity of tinnitus. Diagnosis typically incorporates a detailed medical history, clinical examinations, and psychological assessments.
Medical History
Type of Tinnitus
The classification of tinnitus as subjective or objective should be clarified.
Nature of Tinnitus
The pitch should be noted as high, medium, or low, and whether the sound is single-toned or multi-toned. Descriptions of the tinnitus sound, such as buzzing, whistling, hissing, rumbling, or clicking, are relevant. The distinction between pulsatile and non-pulsatile tinnitus, its rhythm, synchronization with cardiac pulsation, and possible relation to breathing cycles are important. Changes in the quality or pitch of the sound are also worth noting.
Characteristics of Tinnitus
The laterality and precise location of the tinnitus, whether it is continuous or intermittent, the duration of intermittent episodes, and whether the pattern fluctuates should be assessed.
Timeline of the Condition
The onset time, duration, progress, prior treatments, and current status should be recorded.
Loudness of Tinnitus
The intensity of the sound may be evaluated relative to environmental or daily ambient sounds.
Associated Symptoms
The concomitance of hearing loss or vertigo and the sequence of their appearance should be investigated.
Severity of Tinnitus
The effects on emotional health, work performance, daily life, learning, and sleep should be examined. The degree of distress caused by tinnitus, whether it leads to negative emotions, anxiety, or depression, and its causal relationship with psychological factors are worth evaluating. The possibility of gradual adaptation to the condition should also be considered. Various assessment tools are available for evaluating tinnitus severity, including the Tinnitus Handicap Inventory (THI), Tinnitus Reaction Questionnaire (TRQ), Tinnitus Questionnaire (TQ), Tinnitus Severity Index (TSI), Tinnitus Handicap Questionnaire (THQ), and Tinnitus Functional Index (TFI). The THI is commonly used in clinical practice.
Triggering or Aggravating Factors and Relief Measures
Influences that exacerbate or relieve tinnitus symptoms need to be addressed.
Possible Causes
Relevant factors include previous otologic disease history, systemic disease history, head trauma, acoustic trauma, noise exposure, use of ototoxic medications, cardiovascular conditions, allergic disorders, menstrual history, hypertension, diabetes, or other potential causes.
Family History
Any family history related to tinnitus should be reviewed.
Examination
Physical examinations and supplementary tests should aim to provide information about the location, cause, and severity of the tinnitus.
Psychological Assessment
Given the reciprocal relationship between tinnitus and anxiety, a mental health evaluation in collaboration with psychological professionals should be considered.
Treatment
Although the mechanisms of tinnitus remain unclear, and its causes are complex and often difficult to diagnose, the majority of patients can achieve effective symptom control with appropriate treatment. Even if the tinnitus does not completely disappear, it can be managed in a way that minimizes its impact on the patient’s work and daily life.
Treatment for tinnitus should be individualized based on the specifics of each patient's condition. In cases where the cause is clear, treatment should target the underlying etiology. For cases where the cause is difficult to determine, behavioral and cognitive therapy may be utilized, focusing on addressing the patient's irrational perceptions. This therapy involves changing their views and attitudes toward themselves, others, or certain situations to improve psychological well-being. Medications and sound-based therapies can serve as auxiliary measures, helping to alleviate emotional distress, improve sleep quality, and reduce the interference of tinnitus on sensory perception.
Etiological Treatment
For patients with identifiable and treatable primary conditions, targeting the underlying disease or undergoing surgical procedures often leads to a reduction or resolution of tinnitus symptoms. Examples include tinnitus caused by ear canal cerumen impaction, middle ear effusion, sigmoid sinus diverticulum, or otosclerosis.
Tinnitus Retraining Therapy (TRT)
This therapy is based on Jastreboff's neurophysiological model of tinnitus and requires collaboration among otolaryngologists, audiologists, therapists, and psychologists. Through long-term retraining, the nervous system is guided to reintegrate its sensory inputs, aiming to rebuild the auditory system’s filtering function, decrease central excitability, increase inhibitory responses, and eventually halt auditory perception of tinnitus. TRT involves two main components: counseling and sound therapy. Counseling includes preliminary psychological assessment and treatment, where trained professionals explain tinnitus-related issues to reduce the patient’s concerns and negative emotions. Sound therapy involves the use of low-level natural sounds (such as rain, ocean waves, or flowing water), music, songs, or speech recordings. These sounds interfere with the perception of tinnitus and help redirect the patient's attention. Unlike sound masking therapy, sound therapy uses neutral sounds, which may include natural sounds, narrowband or broadband noises, or noises selected by the patient. The treatment period is generally long, often lasting between 12 and 24 months.
Hearing Aids
For patients with bothersome tinnitus accompanied by hearing loss, assessment for hearing aid use could be beneficial. Studies have shown that hearing aids improve quality of life by addressing hearing loss and reducing the focus on tinnitus. For severe sensorineural hearing loss associated with tinnitus, cochlear implants have recently been reported as effective for tinnitus suppression.
Cognitive Behavioral Therapy (CBT)
CBT is recommended for patients experiencing persistent and disruptive tinnitus. Initially developed to treat depression and anxiety, CBT has been proven to mitigate the distress associated with tinnitus. This therapy provides guidance to help patients identify negative thoughts that contribute to stress and reframe them into more constructive perspectives.
Medication Therapy
Although numerous medications have been used in tinnitus treatment, none has been definitively proven to cure tinnitus completely. Studies suggest that medication therapy is more effective for tinnitus that has lasted less than three months. Commonly used drug categories include:
- Anti-anxiety and Antidepressant Medications: These may have varying degrees of side effects and require cautious use, such as alprazolam or estazolam.
- Anticonvulsant Medications: Common options include carbamazepine, clonazepam, aminooxyacetic acid, and lamotrigine.
- Vasodilators: These improve microcirculation in the inner ear and include medications such as betahistine, prostaglandin E2, and calcium channel blockers.
- Local Anesthetics: Drugs like procaine or lidocaine can block neural junctions, providing short-term relief for tinnitus caused by cochlear or retrocochlear disorders.
Other Approaches
Additional treatments include sound masking therapy, biofeedback therapy, electrical stimulation therapy, and repetitive transcranial magnetic stimulation (rTMS), among others.