What is the most likely cause of unilateral left-sided tinnitus with intermittent left eyelid myokymia?

Unilateral Left-Sided Tinnitus with Eyelid Myokymia: Diagnostic Approach

You need urgent imaging with MRI of the internal auditory canals and brain with contrast to rule out vestibular schwannoma, cerebellopontine angle lesions, or demyelinating disease, as unilateral tinnitus combined with neurologic symptoms (even seemingly benign eyelid twitching) represents a red flag requiring immediate investigation. 1, 2

Critical Diagnostic Distinctions

The combination of unilateral tinnitus with ipsilateral eyelid myokymia is not a benign presentation and demands thorough evaluation:

• Unilateral tinnitus automatically triggers imaging requirements according to the American College of Radiology, as it has a higher likelihood of identifiable structural pathology compared to bilateral presentation 1
• Eyelid myokymia, while typically benign when isolated, can rarely represent the first manifestation of serious neurologic disease including multiple sclerosis, brainstem lesions, or posterior fossa pathology when it occurs with other symptoms 3, 4
• The ipsilateral nature of both symptoms (left tinnitus + left eyelid tic) raises concern for a common underlying lesion affecting the auditory pathway and facial nerve 4

Most Likely Differential Diagnoses

Primary Concern: Vestibular Schwannoma (Acoustic Neuroma)

• Vestibular schwannoma almost always causes unilateral tinnitus with asymmetric hearing loss and can produce facial nerve irritation manifesting as facial twitching 2
• This represents the most critical diagnosis to exclude, as delayed treatment can lead to permanent hearing loss, facial paralysis, and life-threatening brainstem compression 2

Secondary Concerns Requiring Exclusion:

• Demyelinating disease (Multiple Sclerosis): Eyelid myokymia progressing to involve other facial muscles within weeks has been documented as the presenting sign of MS with brainstem demyelinating lesions 4
• Other cerebellopontine angle masses: Meningiomas, epidermoid cysts, or other tumors can present identically to vestibular schwannoma 2
• Brainstem pathology: Facial myokymia (distinct from benign eyelid myokymia) indicates brainstem disease and can occur with auditory pathway involvement 4

Less Urgent But Possible:

• Benign eyelid myokymia coinciding with otologic tinnitus: While chronic isolated eyelid myokymia is benign in 86.7% of cases, the combination with unilateral tinnitus changes the risk stratification 3

Immediate Diagnostic Workup

First-Line Imaging (Order Immediately):

MRI of internal auditory canals with contrast using dedicated IAC protocol 1, 2

• This includes thin-section heavily T2-weighted sequences to evaluate for small vestibular schwannomas and vascular loops 1
• Volumetric post-contrast T1-weighted images assess the cerebellopontine angle and can detect demyelinating lesions 1
• This is the single most appropriate test for unilateral non-pulsatile tinnitus without a clinically evident cause 1, 2

Essential Concurrent Testing:

Comprehensive audiologic examination within 4 weeks 2, 5

• Pure tone audiometry, speech audiometry, and acoustic reflex testing 2
• Asymmetric hearing loss strongly increases suspicion for vestibular schwannoma and changes management urgency 1, 2

Critical Physical Examination Elements:

• Detailed otoscopic examination to exclude middle ear pathology, cerumen impaction, or vascular retrotympanic masses 1, 2
• Comprehensive neurologic examination focusing on:
  • Facial nerve function (strength, symmetry, other branches beyond eyelid) 4
  • Trigeminal nerve function (sensation, corneal reflex) 4
  • Cerebellar signs (ataxia, dysmetria, nystagmus) 4
  • Other cranial nerve deficits 2
• Characterize the eyelid myokymia: Is it truly limited to the eyelid, or does it involve other facial muscles? Progression beyond the eyelid dramatically increases concern for serious pathology 4

Key Clinical Questions to Elicit

Tinnitus Characteristics:

• Is it pulsatile or non-pulsatile? Pulsatile tinnitus has vascular etiology in >70% of cases and requires different imaging (CTA) 1, 6, 7
• Constant or intermittent? 8
• High-pitched ringing or low-pitched roaring? High-pitched suggests cochlear pathology; low-pitched suggests middle ear or Meniere's disease 9, 8
• Any associated hearing loss, fullness, or vertigo? This triad suggests Meniere's disease 9, 8

Myokymia Characteristics:

• Duration and progression: Benign eyelid myokymia typically begins as intermittent weekly spasms progressing to daily over months, but remains isolated to the eyelid 3
• Has it spread to other facial areas? Progression to brow, cheek, or lip within days to weeks is a red flag for MS or brainstem disease 4
• Any triggers or modulating factors? 8

Common Pitfalls to Avoid

• Dismissing unilateral tinnitus as benign without imaging: The American Academy of Otolaryngology makes a strong recommendation FOR imaging when tinnitus is unilateral, as vestibular schwannoma can present with isolated tinnitus before hearing loss becomes apparent 1, 2
• Assuming eyelid myokymia is always benign: While chronic isolated eyelid myokymia is benign in most cases, the combination with unilateral tinnitus on the same side demands exclusion of structural pathology 3, 4
• Ordering CT instead of MRI: CT has poor sensitivity for small vestibular schwannomas and cannot adequately visualize the internal auditory canal or detect demyelinating lesions 1
• Delaying audiometry: Baseline hearing assessment is essential for monitoring progression and guides treatment decisions if pathology is found 2, 5
• Failing to perform a thorough neurologic examination: Subtle additional cranial nerve deficits may be present and significantly narrow the differential diagnosis 4

If Initial MRI is Negative

• Reassess clinical progression: If eyelid myokymia spreads to other facial muscles or new neurologic symptoms develop, repeat imaging is warranted 4
• Consider alternative diagnoses: Benign eyelid myokymia with coincidental otologic tinnitus (sensorineural hearing loss, noise exposure, presbycusis) becomes more likely 2, 3
• Treat symptomatically: Botulinum toxin injection provides excellent relief for chronic eyelid myokymia if it persists and is bothersome 3