Abducens (VI) Nerve Palsy
Abducens (VI) nerve palsy causes a selective weakness of the lateral rectus muscle resulting in impaired abduction of the eye, manifest clinically as diplopia on lateral gaze, or on shifting gaze from a near to a distant object.
Abducens (VI) nerve palsy may be due to:
- Microinfarction in the nerve, due to hypertension, diabetes mellitus
- Raised intracranial pressure: a "false-localizing sign", possibly caused by stretching of the nerve in its long intracranial course
over the ridge of the petrous temporal bone
- Nuclear pontine lesions: congenital (e.g., Duane retraction syndrome, Möbius syndrome).
Isolated weakness of the lateral rectus muscle may also occur in myasthenia gravis. In order not to overlook this fact, and miss a potentially treatable condition, it is probably better to label isolated abduction failure as "lateral rectus palsy", rather than abducens nerve palsy, until the etiological diagnosis is established.
Excessive or sustained convergence associated with a midbrain lesion (diencephalic-mesencephalic junction) may also result in slow or restricted abduction (pseudo-abducens palsy, "midbrain pseudo-sixth").