What causes tinnitus?

What Causes Tinnitus

Tinnitus is not a disease but a symptom resulting from underlying auditory or neurological dysfunction, most commonly sensorineural hearing loss (SNHL), which accounts for the majority of cases. 1, 2

Primary Mechanism: Auditory System Dysfunction

The fundamental cause of tinnitus involves abnormal neural activity in the central auditory system triggered by peripheral auditory damage or dysfunction. 3

Sensorineural hearing loss is the single most common underlying cause, particularly in patients with bothersome tinnitus and no obvious ear pathology. 1, 2 This occurs through several mechanisms:

• Noise exposure (occupational or recreational) damages cochlear hair cells, leading to both hearing loss and tinnitus 2
• Age-related hearing loss (presbycusis) progressively degrades auditory function 2
• Cochlear synaptopathy ("hidden hearing loss") triggers irreversible degeneration of auditory nerve fibers without affecting outer hair cells, causing difficulty understanding speech in noisy environments 2
• Ototoxic medications directly damage the auditory system 2

Central Nervous System Changes

When peripheral auditory input is reduced, the central nervous system undergoes maladaptive changes that generate the perception of sound. 3

Key neurological mechanisms include:

• Elevated spontaneous neuronal firing rates in auditory pathways due to auditory deprivation 3
• Increased neuronal synchronization in central auditory structures 3
• Auditory cortical reorganization and changes in tonotopic mapping 3
• Dysregulation of the limbic system and central auditory cortex, explaining the emotional distress associated with tinnitus 3

Secondary Causes Requiring Identification

While most tinnitus stems from SNHL, clinicians must identify treatable secondary causes. 1

Otologic causes:

• Cerumen impaction 4
• External ear infection 4
• Middle ear effusion 4
• Otosclerosis (conductive hearing loss) 1, 2
• Menière's disease 1, 5
• Sudden sensorineural hearing loss 1, 2

Vascular causes (typically pulsatile tinnitus):

• Arterial dissection, fibromuscular dysplasia 2
• Dural arteriovenous fistulas, arteriovenous malformations 2, 5
• Carotid artery atherosclerosis 5, 4
• Transverse sinus stenosis, sigmoid sinus abnormalities 2
• Paragangliomas (glomus tumors) 2, 5

Structural/bony abnormalities:

• Superior semicircular canal dehiscence 2
• High jugular bulb 2
• Intracranial hypertension or hypotension 2, 5

Neurologic causes:

• Vestibular schwannoma (acoustic neuroma) - particularly with unilateral tinnitus 5, 4
• Neurodegeneration 2
• Traumatic brain injury 6

Psychogenic factors:

• Anxiety and depression both contribute to and result from tinnitus 2, 7, 6

Clinical Classification That Guides Diagnosis

Subjective vs. Objective:

• Subjective tinnitus (70-80% of cases) is perceived only by the patient and typically relates to SNHL 1, 2
• Objective tinnitus can be heard by the examiner and should prompt evaluation for vascular abnormalities 2

Pulsatile vs. Non-pulsatile:

• Pulsatile tinnitus synchronizes with heartbeat and is often vascular in origin, requiring thorough vascular evaluation 1, 2
• Non-pulsatile tinnitus is continuous and almost always subjective, representing the more common variant 1, 2

Unilateral vs. Bilateral:

• Unilateral tinnitus warrants more aggressive investigation due to higher risk of underlying pathology like vestibular schwannoma 8, 4
• Bilateral tinnitus without focal neurological findings typically does not require imaging 1

Critical Risk Factors

Age is the strongest demographic risk factor, with prevalence increasing from 1.6% in adults aged 18-44 years to 9.0% in those over 60 years. 1, 2

Other major risk factors include:

• Occupational and recreational noise exposure 2, 3, 5
• Head or cervical trauma 3, 6
• Military service 6
• Inflammatory diseases of the ear 3
• Depression and anxiety disorders 3, 7, 6

Important Clinical Pitfalls

Patients with tinnitus accompanied by severe anxiety or depression require prompt identification and intervention, as suicide has been reported in patients with tinnitus who have coexisting psychiatric illness. 1, 2, 8 This represents a true psychiatric emergency that demands immediate attention beyond the tinnitus itself.

Approximately 20% of adults with tinnitus require clinical intervention, though most patients adapt to the phantom sound over time. 1, 2, 3 The key is distinguishing bothersome from non-bothersome tinnitus and identifying the subset requiring aggressive workup for serious underlying pathology.