What is the differential diagnosis for a patient presenting with unilateral muffled hearing, considering potential causes such as middle ear effusion, eustachian tube dysfunction, perforated eardrum, or otosclerosis?

Differential Diagnosis for Unilateral Muffled Hearing

The differential diagnosis for unilateral muffled hearing must first distinguish between conductive and sensorineural causes through otoscopy and tuning fork testing, as this fundamentally determines the diagnostic pathway and urgency of evaluation. 1

Initial Classification: Conductive vs. Sensorineural

Conductive Hearing Loss (Abnormal Otoscopy Expected)

Middle Ear Effusion (OME)

• Fluid in the middle ear without signs of acute infection, appearing as decreased tympanic membrane mobility on pneumatic otoscopy 1
• Most common in children aged 6 months to 4 years, but occurs in adults with eustachian tube dysfunction 1, 2
• Tympanogram shows flat or nearly flat tracing when middle ear is filled with fluid 1
• At least 25% of OME episodes persist for ≥3 months and cause conductive hearing loss 1

Eustachian Tube Dysfunction

• Protective closing failure leads to negative middle ear pressure and subsequent retraction of the tympanic membrane 3
• Repetitive sniff-induced barotrauma evacuates the middle ear cavity, causing persistent negative pressure 3
• May present with ear fullness, pressure sensation, and muffled hearing without visible effusion 3

Cerumen Impaction

• Must be removed prior to establishing any diagnosis of hearing loss 1
• Visible on otoscopic examination as complete or partial canal obstruction 1

Tympanic Membrane Perforation

• Visible defect in the tympanic membrane on otoscopy 1
• Weber test lateralizes to the affected ear 1

Cholesteatoma

• Chronic inflammatory middle ear pathology requiring CT differentiation from simple otitis media 1, 4
• May present with retrotympanic mass or visible debris on otoscopy 1

Otosclerosis

• Presents with unilateral conductive hearing loss, rarely with imbalance symptoms 5
• Critical distinguishing feature: ear appears completely normal on otoscopy 5
• Rinne test shows bone conduction better than air conduction 1

Sensorineural Hearing Loss (Normal Otoscopy Expected)

Idiopathic Sudden Sensorineural Hearing Loss (ISSNHL)

• This is a medical emergency requiring evaluation and treatment within 2 weeks of symptom onset 4
• Patients often report tinnitus (63-75% of cases), ear fullness, and sometimes vertigo 1
• Weber test lateralizes away from the affected ear 1
• 86% of patients with unilateral SSNHL report hearing handicap 4

Vestibular Schwannoma (Acoustic Neuroma)

• Occurs in 63-75% of patients presenting with unilateral tinnitus and hearing loss 1, 6
• MRI head and internal auditory canal without and with IV contrast is mandatory for unilateral symptoms 1, 6, 4
• Unilateral tinnitus has higher risk of underlying structural pathology than bilateral tinnitus 6, 4

Ménière's Disease

• Most common cause when preceded by fluctuating hearing loss 1
• Hearing declines in stepwise or fluctuating manner, occasionally presenting suddenly 1
• Associated with vertigo and low-frequency hearing loss pattern 1

Infectious Causes

• Otosyphilis: Can cause sudden unilateral hearing loss and tinnitus; prevalence may be increasing 7
• Viral infections (HSV, VZV, HIV): Look for pinna/canal vesicles and facial weakness in Ramsay Hunt syndrome 1
• Bacterial meningitis: Associated with headache, fever, other cranial nerve palsies 1
• Lyme disease, tuberculosis, fungal infections: Consider based on exposure history 1

Autoimmune Inner Ear Disease

• Presents with hearing fluctuation and vertigo 1
• May have bilateral involvement at onset 1

Ototoxic Medications

• Associated with vestibular loss and oscillopsia 1
• Review medication history for aminoglycosides, chemotherapy agents, loop diuretics 1

Trauma-Related

• Recent head trauma, acoustic trauma, or barotrauma should be identified in history 1
• Temporal bone fracture may show Battle's sign; cochlear concussion may occur without visible fracture 1

Red Flags Requiring Urgent Evaluation

The following features suggest nonidiopathic causes requiring immediate workup: 1

• Bilateral sudden hearing loss
• Antecedent fluctuating hearing loss
• Focal neurologic symptoms (headache, confusion, diplopia, dysarthria, focal weakness, ataxia, facial weakness)
• Concurrent eye pain, redness, lacrimation, photophobia
• Gaze-evoked or downbeat nystagmus
• Concurrent severe bilateral vestibular loss with oscillopsia

Diagnostic Approach Algorithm

Step 1: Otoscopic Examination

• If abnormal → pursue conductive causes (OME, perforation, cholesteatoma, cerumen) 1
• If normal → pursue sensorineural causes (ISSNHL, vestibular schwannoma, Ménière's) 1, 5

Step 2: Tuning Fork Testing (Weber and Rinne)

• Weber lateralizes to affected ear → conductive loss 1
• Weber lateralizes away from affected ear → sensorineural loss 1
• Rinne: bone > air conduction → conductive loss 1

Step 3: Audiometry

• Mandatory for all patients with unilateral muffled hearing 4
• Distinguishes conductive, sensorineural, or mixed hearing loss 1
• Quantifies degree of hearing loss 1

Step 4: Imaging (When Indicated)

• For non-pulsatile unilateral symptoms with sensorineural loss: MRI head and internal auditory canal without and with IV contrast 1, 6, 4
• For pulsatile symptoms: CT temporal bone without contrast plus CTA head and neck with contrast 6, 4
• Do NOT order routine CT head for presumptive SSNHL 1

Critical Pitfalls to Avoid

• Never dismiss unilateral symptoms without imaging—vestibular schwannomas and vascular abnormalities require exclusion 6, 4
• Never delay audiologic evaluation in unilateral symptoms, as early identification of SSNHL improves treatment outcomes 4
• Never assume otosclerosis without normal otoscopy—other conductive causes have visible abnormalities 5
• Never ignore fluctuating hearing history—this suggests Ménière's disease, autoimmune inner ear disease, or Cogan's syndrome rather than idiopathic SSNHL 1
• Intermittent symptoms do not exclude serious structural pathology 6