What is the diagnosis and management of Skew Deviation?

Diagnosis and Management of Skew Deviation

Skew deviation is a vertical misalignment of the eyes caused by disorders of vestibular pathways that requires urgent neuroimaging and referral to neurology or otolaryngology specialists for evaluation of potentially serious underlying causes such as stroke, demyelination, or mass lesions. 1

Definition and Pathophysiology

Skew deviation is a vertical strabismus associated with:

• Disorders of end-organ vestibular pathways (e.g., vestibular neuronitis)
• Supranuclear utriculo-ocular pathway disorders in the posterior fossa (brainstem and cerebellum)
• Commonly part of the ocular tilt reaction, which includes:
  • Vertical misalignment (skew)
  • Ocular torsion
  • Head tilt toward the hypotropic eye
  • Tilt of the subjective visual vertical 1

Clinical Presentation

Symptoms

• Vertical diplopia (87% of patients)
• Blurred vision (11% of patients, more common with misalignment <3 prism diopters) 2
• Perceived tilting of the visual world
• Torticollis (head tilt)
• May have associated vertigo, dizziness, nausea, and vomiting 1

Key Examination Findings

• Vertical misalignment ranging from 1-30 prism diopters (median 5 PD) 2
• May be comitant (64%) or incomitant 2
• Characteristic ocular torsion:
  • Hypertropic eye shows fundus incyclotorsion
  • Hypotropic eye shows fundus excyclotorsion 1, 3
• Head tilt toward the shoulder of the hypotropic eye
• Associated neurological signs in 85% of patients:
  • Nystagmus (most common)
  • Gaze paresis
  • Ataxia
  • Saccadic pursuit
  • Internuclear ophthalmoplegia 2

Diagnostic Approach

Distinguishing from Fourth Nerve Palsy

Critical distinction as skew deviation often indicates serious neurological pathology requiring urgent attention 1

1. Ocular torsion pattern:

   • Skew deviation: Hypertropic eye shows incyclotorsion
   • Fourth nerve palsy: Hypertropic eye shows excyclotorsion 1, 3

2. Upright-supine test:

   • In skew deviation: Hypertropia typically reduces by >50% when measured in supine position (sensitivity 80%, specificity 100%)
   • Note: This test may be less reliable in acute skew deviation (onset within 2 months) 1, 3

3. Associated findings:

   • Skew deviation: Often has other neurological signs
   • Fourth nerve palsy: Usually isolated ocular finding 1

Complete Examination Should Include:

• Sensorimotor evaluation with three-step test and upright-supine test
• Assessment for other neuro-ophthalmic signs (Horner's syndrome, cranial nerve palsies, INO, nystagmus)
• Fundus examination for papilledema or optic atrophy
• Visual field testing 1

Etiology

• Stroke (52% of cases): Most common cause, affecting thalamus, brainstem, or cerebellum 2
• Demyelination: More common in females 1
• Vestibular neuronitis: Associated with severe vertigo, nausea, vomiting 1, 4
• Mass lesions: Tumors, especially of the brainstem 2
• Other causes: Trauma, infection, hemorrhage, intracranial hypertension 5
• Idiopathic: 11% of patients have skew deviation as the only clinical sign with no imaging abnormalities 2

Management Algorithm

1. Immediate Diagnostic Workup:

   • MRI brain with and without contrast (urgent) to evaluate for stroke, demyelination, or mass lesions 1
   • Referral to neurology and/or otolaryngology specialists 1

2. Acute Management of Symptoms:

   • Prisms for diplopia management while awaiting potential recovery 1
   • Address underlying cause (e.g., stroke management, treatment of demyelinating disease)

3. Long-term Management:

   • Monitor for resolution (occurs in 42% of patients, usually within 3 months but can take up to 12 months) 2
   • For persistent diplopia:
     • Prism spectacles (successful in 62% of patients with persistent diplopia) 2
     • Consider botulinum toxin injection 1
     • Strabismus surgery for cases that don't resolve 1

4. Treatment Goals:

   • Improve binocular vision
   • Control diplopia
   • Reduce tilt of subjective visual vertical 1

Prognosis

• Vestibular neuronitis and transient ischemia may be self-limiting
• More profound ischemic damage or mass lesions often result in long-lasting symptoms 1
• Skew deviation is typically the first sign to resolve (within days), while cyclotorsion and tilt of visual vertical may persist for weeks to months 4
• Accompanying neurological signs, especially ataxia, may persist in 44% of patients and can be more debilitating than the diplopia 2

Clinical Pearls and Pitfalls

• Skew deviation can occur with peripheral vestibular lesions (24% of acute unilateral vestibulopathy cases), not just central causes 6
• Large skew deviations (>3.3 degrees) more likely indicate central lesions 6
• Skew deviation can be the only sign of serious neurological disease in 11% of cases 2
• The classic three-step test alone may not distinguish skew deviation from fourth nerve palsy 1