Typewriter Tinnitus: Definition, Mechanism, and Treatment
Typewriter tinnitus is a rare, distinctive subtype of tinnitus characterized by paroxysmal attacks of staccato, clicking sounds—often described by patients as resembling a typewriter, Morse code, popcorn, or machine-gun fire—caused by neurovascular compression of the cochlear nerve, and it responds remarkably well to carbamazepine. 1
Clinical Characteristics
Typewriter tinnitus presents with several distinguishing features that separate it from common tinnitus:
- Sound quality: Patients describe intermittent, staccato clicking sounds rather than the continuous ringing or buzzing typical of other tinnitus types 2, 3
- Pattern: The tinnitus is paroxysmal and episodic, not continuous 1
- Laterality: Symptoms are predominantly unilateral 3
- Associated symptoms: Frequently accompanied by paroxysmal vertigo, dizziness, facial spasms, and symptoms triggered by head motion 3
- Age distribution: Tends to affect older patients compared to other tinnitus subtypes 3
Underlying Mechanism
The pathophysiology differs fundamentally from typical sensorineural tinnitus:
- Neurovascular compression: Vascular loops (typically from the anterior inferior cerebellar artery) compress the eighth cranial nerve, causing ephaptic transmission and aberrant neural firing 1, 2
- Diagnostic confirmation: Auditory brainstem response (ABR) testing reveals prolonged interpeak latency (IPL) I-III (≥2.3 ms), with longer wave III and V latencies compared to the unaffected ear 2
- Alternative etiologies: Neuroinflammation and demyelinating diseases (including Ramsay Hunt syndrome and neuromyelitis optica spectrum disorders) can also cause typewriter tinnitus 2
Diagnostic Approach
ABR testing is the most valuable diagnostic tool for typewriter tinnitus:
- Key finding: IPL I-III ≥2.3 ms strongly suggests typewriter tinnitus 2
- Comparison: Decreased wave II amplitude on ABR is the most reliable diagnostic sign, distinguishing it from middle ear myoclonic tinnitus 3
- Imaging: MRI with heavily T2-weighted thin-section sequences can detect neurovascular loops in contact with cranial nerve VIII 1
Important distinction: Unlike middle ear myoclonic tinnitus, typewriter tinnitus patients do NOT show acoustic reflex decay perturbation or low loudness discomfort levels 3
Treatment Strategy
Carbamazepine is the first-line treatment with excellent response rates:
- Efficacy: All patients (100%) with typewriter tinnitus exhibit partial or complete response to carbamazepine 3
- Alternative: Oxcarbazepine or gabapentin can be used with similar efficacy 1, 4
- Dosing: Start carbamazepine and titrate to symptom control (specific dosing not provided in guidelines, but clinical practice typically begins at 100-200 mg twice daily)
Critical Prognostic Factors
Relapse after medication withdrawal is common and predictable:
- Relapse rate: 60% of patients experience recurrence after stopping carbamazepine 3
- High-risk features for relapse:
Clinical implication: Patients with IPL I-III >2.4 ms should be counseled about high relapse risk and may require indefinite maintenance therapy rather than attempting drug withdrawal 2
Common Pitfalls to Avoid
- Misdiagnosis as middle ear myoclonus: The staccato quality can mimic middle ear myoclonic tinnitus, but ABR findings (prolonged IPL I-III vs. acoustic reflex abnormalities) distinguish them 3
- Delayed diagnosis: Earlier diagnosis and treatment initiation significantly improve long-term prognosis and reduce relapse risk 3
- Premature drug discontinuation: Given the 60% relapse rate, patients should be carefully selected for withdrawal attempts, avoiding this in high-risk patients 2, 3
- Overlooking associated conditions: Screen for neuroinflammatory and demyelinating diseases, particularly in atypical presentations 2