What are the causes and treatment options for sudden unilateral hearing loss?

Causes of Sudden Unilateral Hearing Loss

Most cases of sudden sensorineural hearing loss (SSNHL) in one ear are idiopathic (85-90% of cases), but you must systematically exclude identifiable causes that require specific treatment, including acoustic neuroma, autoimmune disease, infection, and vascular disorders. 1

Idiopathic SSNHL (Most Common)

• In 85-90% of cases, no underlying cause is identified despite thorough evaluation at initial presentation 1
• The presumed mechanism is acute vascular endolymphatic hydrops, though the exact pathophysiology remains uncertain 2
• Only 10-15% of patients have an identifiable cause at time of presentation, though up to one-third may have a cause identified during long-term follow-up 1

Identifiable Causes Requiring Specific Workup

Neoplastic Causes

• Acoustic neuroma (vestibular schwannoma) and other cerebellopontine angle tumors are critical diagnoses not to miss 3
• These present classically with retrocochlear pattern of sensorineural hearing loss, reduced vestibular response on caloric testing, and pathological auditory brainstem response 3
• MRI offers greater specificity than CT for detecting these lesions 3

Autoimmune Causes

• Autoimmune inner ear disease presents with fluctuating hearing loss and may involve vertigo 1
• Cogan syndrome should be considered, especially with concurrent eye symptoms (pain, redness, lacrimation, photophobia) 1

Infectious Causes

• Meningitis (infectious, inflammatory, or neoplastic) presents with headache, fever, abnormal CSF studies, and possibly other cranial nerve palsies 1
• Lyme disease shows erythema chronicum migrans, abnormal CSF, and fluctuating bilateral audiovestibular symptoms 1
• Syphilis demonstrates abnormal FTA-abs test, bilateral fluctuating hearing loss, and multiorgan involvement 1
• Herpes zoster oticus (Ramsay-Hunt syndrome) presents with otalgia, pinna/ear canal vesicles, facial nerve paresis 1
• HIV otitis shows positive HIV titers, altered T cell counts, and often other cranial neuropathies 1

Vascular Causes

• Stroke or structural lesions may present with sudden hearing loss alongside focal weakness, dysarthria, hemiataxia, encephalopathy, severe headaches, or diplopia 1
• Moyamoya disease can rarely present as sudden unilateral hearing loss due to posterior and middle cerebral artery occlusion 4
• Anomalous carotid anatomy with embolization to the internal auditory artery represents a rare vascular cause 5

Traumatic Causes

• Severe head trauma coincident with hearing loss, including temporal bone fractures 1
• Barotrauma 1
• Recent acoustic trauma 1

Metabolic/Toxic Causes

• Ototoxic medications cause vestibular loss and oscillopsia alongside hearing loss 1
• Lead poisoning presents with learning disabilities and other stigmata 1

Inner Ear Disorders

• Meniere disease shows isolated low-frequency hearing trough and antecedent fluctuating hearing loss 1
• Labyrinthine membrane rupture 5

Red Flags Requiring Immediate Attention

Look specifically for these features that indicate a definable underlying disease: 1

• Sudden onset of bilateral hearing loss (rare and concerning)
• Antecedent fluctuating hearing loss on one or both sides
• Concurrent onset of severe bilateral vestibular loss with oscillopsia
• Accompanying focal neurological symptoms (weakness, dysarthria, hemiataxia, encephalopathy, severe headaches, diplopia)
• Downbeating or gaze-evoked nystagmus
• Brain imaging showing stroke or structural lesion
• Severe head trauma coincident with hearing loss
• Concurrent or recent eye symptoms (pain, redness, lacrimation, photophobia)

Clinical Pitfalls

• The primary presenting symptom is often just ear fullness or blockage, which is non-specific and leads to delayed evaluation 1
• Patients and physicians are frequently not sufficiently concerned by ear blockage, resulting in delayed treatment 1
• New onset of ear blockage or fullness warrants prompt evaluation as it can indicate potentially serious conditions 1
• The presence of vertigo at onset indicates more severe cases and poorer prognosis for hearing recovery 6