Sixth (Abducens) Nerve Palsy

Relevant physical signs

• Abducens nerve palsy
  • Pure horizontal diplopia
  • Esotropia (inward deviation of the eye – unopposed medial rectus) on inspection
  • Paralysis of lateral gaze on the affected side
  • Nystagmus of the contralateral eye on looking towards the affected side
• 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)
  • Pontine syndromes
    • Contralateral hemiparesis – corticospinal tract (Raymond’s)
    • Contralateral hemiparesis, ipsilateral facial nerve palsy –Millard-Gubler syndrome
  • Complex ophthalmoplegia
    • Tachycardia, goitre, tremor – thyroid eye disease
    • Fatigability – ocular myasthenia
    • Grip myotonia – myotonic dystrophy
    • Arreflexia – Miller-Fisher syndrome
    • Scars – trauma, previous surgery
  • Bilateral sixth nerve palsy – false localizing sign
• Nuclear lesions
  • VI nucleus projects via the medial longitudinal fasciculus to the contralateral III nucleus
  • Nuclear lesions hence produce complete lateral gaze palsies
  • g. in right abducens nuclear lesion
    • Failure of abduction of the right eye when looking right
    • Failure of adduction of the left eye when looking right
  • Can be differentiated from a concomitant III nerve lesion by asking the patient to converge
    • Medial gaze not affected in this case

Differential diagnosis

• False localizing sign (raised intracranial pressure), especially in bilateral VI palsies
• Inflammatory
  • Demyelinating disease – multiple sclerosis
  • Giant cell arteritis
  • Sarcoidosis
  • Wegner’s granulomatosis
  • Churg-Strauss syndrome
  • Polyarteritis nodosa
  • Systemic lupus erythematosus
• Infection
  • Lyme disease
  • Syphilis
  • Bacterial meningitis
• Neoplastic
  • Pontine tumour
  • Leptomeningeal carcinomatosis
• Vascular
  • Pontine stroke
  • Basilar artery aneurysm
• Trauma