What investigations are recommended for a patient presenting with bilateral sudden sensorineural hearing loss (SSNHL)?

Investigations for Bilateral Sudden Sensorineural Hearing Loss

Bilateral SSNHL is a medical emergency that mandates aggressive investigation for life-threatening systemic diseases, requiring MRI with dedicated internal auditory canal protocol, comprehensive laboratory workup for autoimmune and infectious etiologies, and consideration of lumbar puncture when meningitis is suspected. 1

Why Bilateral SSNHL Demands Urgent Investigation

Bilateral SSNHL represents a fundamentally different disease entity than unilateral SSNHL and carries a 35-44% mortality rate within 5 years. 2, 3 Most cases (69-100%) have an identifiable underlying systemic cause, compared to predominantly idiopathic unilateral cases. 1, 4, 2 The bilateral presentation indicates severe involvement of both cochlear and vestibular structures and portends worse hearing recovery regardless of treatment. 4, 2

Essential Imaging

MRI Protocol (First-Line Imaging)

• Order MRI of the brain and internal auditory canals with a dedicated IAC protocol including high-resolution 3D T2 sequences (FIESTA/CISS) with slice thickness ≤1mm, T1 sequences with gadolinium contrast, and FLAIR sequences. 5

• This protocol detects vestibular schwannomas, meningeal enhancement suggesting meningitis, eighth nerve inflammation/neuritis, labyrinthitis, labyrinthine hemorrhage, vascular lesions, cerebrovascular disease, demyelinating lesions (multiple sclerosis), and neoplastic processes including carcinomatous meningitis and intravascular lymphomatosis. 1, 5

• MRI reveals abnormalities in 57% of SSNHL cases, with 11% directly related to hearing loss. 5

CT Imaging

• Do NOT order routine CT of the head in the initial evaluation—this is a strong recommendation against based on systematic reviews. 1

• CT temporal bone may be considered only if trauma history exists (looking for temporal bone fracture, Battle's sign) or if MRI is contraindicated. 1

Comprehensive Laboratory Workup

Infectious Disease Testing

• Syphilis serology (FTA-abs or treponemal testing) - bilateral SSNHL can be the presenting manifestation of neurosyphilis, particularly in immunocompromised patients. 1, 5

• HIV testing - HIV-associated infections and inflammatory conditions cause bilateral SSNHL. 1, 5

• Viral serologies including HSV, VZV (especially if vesicles present on pinna/ear canal or facial weakness suggesting Ramsay Hunt syndrome), and other viral pathogens. 1

• Lyme disease testing if epidemiologically appropriate. 1

• Tuberculosis and fungal studies if risk factors present. 1

Autoimmune/Inflammatory Workup

• Antinuclear antibodies (ANA) - screens for systemic autoimmune diseases including systemic sclerosis, which can present with bilateral SSNHL as the initial symptom. 6, 7

• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) - elevated in autoimmune inner ear disease, Cogan's syndrome, and other inflammatory conditions. 1

• Angiotensin-converting enzyme (ACE) level - elevated in sarcoidosis, which causes bilateral SSNHL with bilateral vestibular loss. 1

• Rheumatoid factor, anti-CCP antibodies, complement levels (C3, C4) - autoimmune inner ear disease affects 3.83% of bilateral SSNHL cases and has worse prognosis than idiopathic cases. 7

• Antiphospholipid antibodies - hyperviscosity syndrome causes bilateral SSNHL with mucous membrane bleeding and retinopathy. 1

Metabolic and Hematologic Studies

• Complete blood count with differential - screens for leukemia, lymphoma, and hyperviscosity syndrome. 1

• Serum protein electrophoresis - detects hyperviscosity syndrome and multiple myeloma. 1

• Lactate level - elevated in mitochondrial disorders (MELAS) which present with bilateral SSNHL, confusion, stroke-like episodes, and MRI white matter changes. 1

• Lead level if exposure history or other stigmata present. 1

Additional Testing Based on Clinical Context

• Thyroid function tests - thyroid disease associates with autoimmune inner ear disease. 1

• Coagulation studies if stroke suspected based on focal neurologic findings. 1

Lumbar Puncture Indications

• Perform lumbar puncture with CSF analysis if meningitis is suspected clinically (headache, fever, other cranial nerve palsies) or if MRI shows meningeal enhancement. 1, 5

• CSF studies should include cell count, protein, glucose, Gram stain, bacterial culture, VDRL (for neurosyphilis), cryptococcal antigen (if immunocompromised), and cytology if carcinomatous meningitis suspected. 1, 5

Audiometric and Vestibular Testing

• Complete audiometry with pure-tone air and bone conduction testing must be performed as soon as possible and within 14 days of symptom onset. 5

• Vestibular testing battery including caloric testing and vestibular-evoked myogenic potentials (VEMP - both cervical and ocular) - 81-100% of bilateral SSNHL patients have abnormal vestibular testing, indicating severe bilateral involvement of both cochlear and vestibular structures. 2

• This extensive vestibular involvement distinguishes bilateral from unilateral SSNHL and helps establish disease severity. 2

Clinical Red Flags Requiring Specific Investigation

Neoplastic Causes (31% of bilateral SSNHL cases)

• Neurofibromatosis II, bilateral vestibular schwannomas, carcinomatous meningitis, intravascular lymphomatosis require MRI with contrast and possibly CSF cytology. 1, 2

Vascular Causes (31% of bilateral SSNHL cases)

• Vertebrobasilar stroke presents with vertigo, dysarthria, facial weakness, ataxia, nystagmus, and unilateral numbness - requires MRI/MRA of vertebrobasilar vasculature urgently. 1, 2

Infectious Causes (6% of bilateral SSNHL cases)

• Meningitis (bacterial, viral, fungal, tuberculous) requires lumbar puncture. 1, 2

Critical Pitfalls to Avoid

• Never assume bilateral SSNHL is idiopathic - 69-100% have identifiable causes compared to predominantly idiopathic unilateral cases. 1, 4, 2

• Do not delay investigation while initiating corticosteroid treatment - start steroids immediately if within 2 weeks of onset, but pursue diagnostic workup simultaneously as bilateral SSNHL has 35-44% mortality. 5, 2, 3

• Recognize that simultaneous bilateral SSNHL has significantly worse prognosis than sequential bilateral involvement - 89% present with severe/profound loss versus 59% in sequential cases, with worse recovery rates. 4

• Patients with bilateral SSNHL and systemic autoimmune disease have more severe initial impairment, higher percentage of bilateral involvement, lower response to treatment, and worse prognosis than idiopathic cases. 7