What could be causing a female patient's sudden onset of vertigo, characterized by head spinning, inability to focus her eyes, nausea with movement, balance problems, and flashing lights when moving her head, with no prior history of vertigo, but a history of sudden hearing loss in one ear and recent steroid use for sinus inflammation?

Acute Labyrinthitis or Posterior Circulation Stroke Requiring Urgent Evaluation

This patient's presentation of sudden-onset severe vertigo with flashing lights, inability to focus eyes, and history of sudden hearing loss in one ear most likely represents acute labyrinthitis, but posterior circulation stroke must be urgently excluded given the severity and associated visual symptoms.

Immediate Clinical Assessment

The combination of severe vertigo with visual symptoms (flashing lights, inability to focus) and prior unilateral hearing loss creates a critical diagnostic challenge requiring urgent evaluation 1, 2.

Key Distinguishing Features Present

Red flags requiring immediate attention:

• Flashing lights with vertigo suggest possible central pathology or severe vestibular dysfunction 2
• Inability to focus eyes may indicate central vestibular involvement 2
• Complete inability to stand suggests severe vestibular dysfunction disproportionate to typical BPPV 2
• History of sudden hearing loss in one ear raises concern for progressive inner ear pathology or vascular events 3, 4

Most Likely Diagnosis: Acute Labyrinthitis

Labyrinthitis is characterized by sudden severe vertigo with profound hearing loss and prolonged vertigo lasting >24 hours, which distinguishes it from other vestibular disorders 5. This patient's presentation fits this pattern:

• Severe rotational vertigo with nausea 5
• Associated with prior hearing loss episode 5
• Symptoms worse with movement, better with stillness 5
• Not episodic or fluctuating like Ménière's disease 6, 5
• Duration >24 hours (started last night, continuing today) 5

Critical Differential: Posterior Circulation Stroke

Despite the likely diagnosis of labyrinthitis, stroke must be excluded because sudden hearing loss and vertigo can be initial symptoms of vertebrobasilar ischemic stroke 3. The research evidence demonstrates that sudden hearing loss with vertigo preceded cerebellar artery infarction in documented cases 3.

When to Suspect Stroke Over Labyrinthitis

The following features would mandate immediate MRI 1, 2:

• Severe imbalance disproportionate to vertigo (present in this patient) 2
• Visual disturbances beyond typical nystagmus (flashing lights are concerning) 2
• Any focal neurological deficits 2
• Inability to stand or walk (present in this patient) 1, 2

Recommended Diagnostic Approach

Immediate Bedside Examination

Perform targeted neurological assessment looking for:

• Speech difficulties (dysarthria/dysphasia) 2
• Swallowing difficulties 2
• Motor or sensory deficits in limbs 2
• Pupillary changes or Horner's syndrome 2
• Nystagmus pattern: downbeating, direction-changing, or baseline nystagmus suggest central pathology 1, 2

HINTS Examination (if trained examiner available)

The HINTS examination has 100% sensitivity for detecting stroke when performed by trained practitioners 1. Central features include:

• Normal head impulse test 1
• Direction-changing or vertical nystagmus 1
• Present skew deviation 1

Imaging Decision

Given this patient's red flags (severe imbalance, inability to stand, visual symptoms, prior hearing loss), MRI brain without contrast should be obtained urgently 1. The American College of Radiology recommends MRI for:

• Abnormal neurologic examination 1
• High-risk features including sudden hearing loss 1, 2
• Inability to stand or walk 1, 2

Do not rely on CT head, as it has <1% diagnostic yield for isolated dizziness and misses most posterior circulation infarcts 1.

Management Based on Final Diagnosis

If Labyrinthitis Confirmed (after stroke excluded)

Labyrinthitis causes sudden severe vertigo with profound hearing loss and prolonged vertigo (>24 hours), with vertigo and nausea accompanying hearing loss 6, 5. Treatment includes:

• Symptomatic management with vestibular suppressants like meclizine for acute severe vertigo 7
• Steroid therapy is indicated given her recent steroid use for sinus inflammation and history of sudden hearing loss 8, 9, 10
• High-dose intravenous dexamethasone (16 mg/day) or oral methylprednisolone (64 mg/day) for 4 days, then tapered over 8 days 4
• Vestibular rehabilitation therapy once acute phase resolves 1

Connection to Prior Hearing Loss

The patient's history of sudden hearing loss in one ear is highly relevant 4. Vestibular dysfunction is associated with disease severity in sudden sensorineural hearing loss patients 4. Her prior hearing loss episode may represent:

• Previous labyrinthitis episode 6
• Underlying inner ear vulnerability 4
• Possible autoimmune inner ear disease (steroid-responsive) 6

Critical Pitfalls to Avoid

• Do not assume absence of focal neurologic deficits excludes stroke - 75-80% of patients with posterior circulation infarct have no focal deficits 1
• Do not dismiss visual symptoms (flashing lights) as benign without excluding central pathology 2
• Do not confuse labyrinthitis with vestibular neuritis - vestibular neuritis causes vertigo WITHOUT hearing loss, while labyrinthitis affects both vestibular and cochlear portions 5
• Do not delay imaging in patients with inability to stand/walk, as this represents severe imbalance requiring urgent evaluation 1, 2

Prognosis Considerations

Patients with vertigo accompanying sudden hearing loss have worse initial hearing thresholds and poorer hearing recovery after steroid treatment 4. The presence of vertigo is associated with:

• More severe initial disease 4
• Lower hearing improvement after treatment (20.9 dB vs 25.0 dB in those without vertigo) 4
• Involvement of vestibular organs, particularly the utricle and lateral semicircular canal 4