MRCP PACES Cranial Neuropathies Third (Oculomotor) Nerve Palsy

Relevant physical signs

  • Third nerve palsy
    • Complete oculomotor palsy
      • Complete ptosis
      • Dilated pupil (unopposed sympathetic action)
        • Loss of efferent pupillary reflex on that side
      • Down-and-out eye (unopposed lateral rectus, superior oblique)
    • Partial palsy: any combination of the above
    • Eye movements affected
      • Superior gaze (superior rectus)
      • Inferior gaze (inferior rectus)
      • Adduction (medial rectus)
      • Upward convergence (inferior oblique)
    • Oculomotor nuclei innervate the ipsilateral eye. Exceptions:
      • Superior rectus sub-nucleus sends projections to the contralateral eye
      • Levator palpabrae on both sides innervated by the same central sub-nucleus
  • Isolated third nerve palsies
    • Surgical
      • Parasympathetic fibres located superficially
      • These are more susceptible to compression
      • Surgical third nerve palsies cause ipsilateral pupil dilation
      • Eye movements relatively spared
    • Medical
      • Due to microvascular infarction within the nerve fibres
      • Tend to cause pupil-sparing lesions of the third nerve
  • Features associated with non-isolated palsies
    • Orbital apex syndrome (II, III, IV, V1, VI)
    • Superior orbital fissure syndrome (III, IV, V1, VI)
    • Cavernous sinus syndrome (III, IV, V1, V2, VI, sympathetic fibres)
    • Midbrain syndromes
      • Contralateral hemiparesis – corticospinal tract (Weber’s)
      • Contralateral ataxia – red nucleus (Benedikt’s) / superior cerebellar peduncle (Claude’s)
    • Complex ophthalmoplegia
      • Tachycardia, goitre, tremor – thyroid eye disease
      • Fatigability – ocular myasthenia
      • Grip myotonia – myotonic dystrophy
      • Arreflexia – Miller-Fisher syndrome
      • Scars – trauma, previous surgery

Differential diagnosis

  • Surgical third nerve palsy (compression)
    • Posterior communicating artery aneurysm
  • Medical third nerve palsy (ischaemia)
    • Diabetes mellitus
    • Giant cell arteritis
    • Systemic lupus erythematosus
    • Wegner’s granulomatosis
    • Churg-Strauss syndrome
    • Polyarteritis nodosa
    • Sarcoidosis
  • Complex ophthalmoplegia
    • Thyroid eye disease
    • Ocular myasthenia
    • Miller-Fisher syndrome
    • Myotonic dystrophy
    • Complete progressive external ophthalmoplegia
    • Trauma
    • Orbital cellulitis
  • Midbrain syndromes
    • Weber’s syndrome
    • Claude’s syndrome
    • Benedikt’s syndrome
  • Orbital syndromes
    • Cavernous sinus syndrome
    • Orbital apex syndrome
    • Superior orbital fissure syndrome
  • False localizing sign: Hutchinson’s pupil (dilated pupil)
    • Caused by ipsilateral uncal herniation and compression of the oculomotor nerve

Investigations

  • Magnetic resonance imaging of the brain
    • Midbrain stroke
    • Midbrain space-occupying lesion
  • Magnetic resonance angiogram
    • Posterior communicating artery aneurysm
  • Medical third nerve
    • Cardiovascular risk factors: FPG, HbA1c, lipid monitoring
    • Vasculitic screen: ANA, ANCA, ENA panel
    • Consider temporal artery biopsy and ESR in older patients (GCA)
  • Consider lumbar puncture
    • Bacterial meningitis
    • Leptomeningeal disease

Management

  • Multidisciplinary team approach
  • Patient education
  • Eye patch for diplopia
  • Consider prism therapy for long-standing deficits
  • Consider neurosurgical referral for aneurysm clipping
  • Control cardiovascular risk factors
  • Antiplatelet therapy for secondary prevention of ischaemic events
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