What are the differential diagnoses for circular nystagmus?

Differential Diagnoses for Circular Nystagmus

Circular nystagmus (also termed rotatory or torsional nystagmus) most commonly indicates either benign paroxysmal positional vertigo (BPPV) affecting the posterior semicircular canal or a central nervous system lesion affecting the cerebellum or cervicomedullary junction, and distinguishing between these requires careful attention to nystagmus characteristics and associated features.

Primary Peripheral Vestibular Causes

Benign Paroxysmal Positional Vertigo (BPPV)

• Posterior canal BPPV classically produces torsional (rotatory) upbeating nystagmus during Dix-Hallpike maneuvers 1
• The nystagmus typically has a latency period, fatigues with repeated testing, and is associated with transient vertigo 2
• Posterior canal BPPV can convert to horizontal nystagmus (lateral canal BPPV) during positioning maneuvers 1

Other Otologic Disorders

The following peripheral vestibular conditions should be considered 1:

• Ménière's disease - episodic vertigo with hearing loss and tinnitus
• Vestibular neuritis - acute unilateral vestibulopathy with spontaneous nystagmus 3
• Labyrinthitis - vestibular symptoms with concurrent hearing loss
• Superior canal dehiscence syndrome - sound/pressure-induced vertigo
• Posttraumatic vertigo - following head injury
• Perilymphatic fistula - pressure-related symptoms

Central Nervous System Causes

Cerebellar and Brainstem Lesions

Central positional nystagmus warrants urgent neuroimaging as it may indicate serious structural pathology 4, 5:

• Cerebellar tumors (hemangioblastoma, metastases) involving midline structures around the fourth ventricle and nodulus can produce apogeotropic positional nystagmus that mimics BPPV 5
• Downbeat nystagmus strongly suggests bilateral floccular lesion or cervicomedullary junction pathology 4, 3
• Lesions dorsolateral to the fourth ventricle or dorsal vermis can cause central paroxysmal positioning vertigo 2, 6

Vascular and Demyelinating Disorders

Neurologic differentials include 1, 4:

• Posterior circulation stroke or transient ischemic attack - acute onset with other brainstem signs
• Vertebrobasilar insufficiency - positional symptoms from transient brainstem ischemia 6
• Demyelinating diseases (multiple sclerosis) - often with other neurological findings
• Vestibular migraine - episodic vertigo with migraine features

Other Central Lesions

• Central nervous system lesions including intracranial tumors 4
• Inner ear lesions affecting central vestibular pathways 1

Critical Distinguishing Features

Red Flags for Central Pathology

The following nystagmus characteristics indicate a central cause rather than peripheral BPPV 4:

• Downbeating nystagmus without a torsional component on Dix-Hallpike maneuver
• Direction-changing nystagmus that does not follow typical BPPV patterns
• Baseline nystagmus present in primary gaze position
• Pure torsional nystagmus without vertical component 3
• Failure to respond to repeated canalith repositioning maneuvers despite typical-appearing positional nystagmus 5

Associated Neurological Signs

Central lesions often present with 3, 5:

• Cerebellar signs (ataxia, dysmetria, dysdiadochokinesia)
• Other oculomotor abnormalities
• Permanent dizziness and gait disorder (especially with downbeat/upbeat nystagmus)
• Asymmetrical or unilateral nystagmus 7

Non-Vestibular Differentials

Other Entities to Consider 1

• Anxiety or panic disorder - may report dizziness without objective nystagmus
• Cervicogenic vertigo - neck-related symptoms
• Medication side effects - various drugs can cause nystagmus
• Postural hypotension - orthostatic symptoms
• Toxic, infectious, and metabolic conditions - systemic causes

Diagnostic Approach Algorithm

Step 1: Characterize the Nystagmus

• Determine if nystagmus is purely torsional/rotatory or has vertical/horizontal components 3
• Assess for latency, duration, and fatigability during positional testing 2
• Check for baseline nystagmus in primary position 4

Step 2: Perform Appropriate Positional Testing

• Dix-Hallpike maneuver for posterior canal BPPV 1
• Supine roll test for lateral canal involvement 1
• Document nystagmus direction and response to repeated maneuvers 5

Step 3: Assess for Central Features

• Perform comprehensive neurological examination looking for cerebellar signs 5
• Evaluate for other oculomotor abnormalities 3
• Consider vestibular function testing including vestibulo-ocular reflex assessment and VEMPs 4

Step 4: Neuroimaging When Indicated

MRI of the brain is the preferred imaging modality when central pathology is suspected 4:

• Obtain MRI for any red flag features suggesting central cause
• Neuroimaging is particularly important for acquired nystagmus to exclude brainstem/cerebellar structural lesions 4
• CT scans may not adequately visualize posterior fossa structures 4
• MRI is mandatory if symptoms are refractory to BPPV treatment 5

Common Pitfalls

• Misdiagnosing central positional nystagmus as BPPV when proper diagnostic maneuvers are not performed or central features are overlooked 4
• Failing to obtain neuroimaging in patients with isolated apogeotropic positional nystagmus refractory to canalith repositioning maneuvers 5
• Relying solely on timing characteristics (latency, duration, fatigability) to differentiate peripheral from central causes, as these features overlap significantly 2
• Missing cerebellar tumors that present with isolated positional nystagmus without other neurological signs 5