Third nerve palsies

Associated symptoms (hemiplegia, tremor, ataxia) suggest a brainstem lesion. See separate sections on localization; this post covers emergencies primarily.

If meningismus or photophobia occur, do lumbar puncture to exclude an infiltrative lesion.

Cavernous sinus. superior orbital fissure lesions-- look for associated fourth nerve palsy, sixth nerve palsy, V1 dysfunction, or Horner's syndrome.

Isolated Third nerve palsy is vasculopathic, ie due to small vessel disease, or due to aneurysm, commonly posterior communicating artery aneurysm. Age greater than 50 and presence of major risk factors such as diabetes, hypertension, and hyperlipidemia favor vasculopathic origin. Third nerve palsy usually presents abruptly but may progress over one or two weeks. Ipsilateral retroorbital or head pain is usually present. Recovery over a period of months is typical. A small degre of anisocoria may be present (10/26 patients per Jacobson) but is almost always less than 2.5 mm.

Aneurysmal third nerve palsy includes younger patients aged 20-50 without risk factors. Pain occurs, but does not differentiate from vasculopathic third nerve palsy. However, pupillary dilatation occurs early, and occurs in 86-95 % of cases, whereas most vasculopathic cases spare the pupil. Trobe's "The Rule of the Pupil" states that in patients with an otherwise complete but pupil-sparing third nerve palsy do not have an aneurysm. IN cases of pupillary sparing aneurysms, other third nerve muscles are spared as well. If the third nerve palsy is partial, the state of the pupil does not help. 30-40 % of patients with partial third nerve palsies harbor an aneurysm. The pattern is different than in vasculopathic third nerve palsies: In vasculopathic cases there is incomplete paresis of all third nerve innervated muscles, but in partial third nerve palsies with aneurysm, patients are more likely to show weakness of just one or more but not all muscles.

MRA and CTA are extremely sensitive for the detection of aneurysms but are not yet 100 %, as they miss aneurysms smaller than 5 mm. Suggestions for on whom to perform angiography include all younger patients without risk factors, even those with low risk (pupil sparing but otherwise complete third nerve palsy). But for patients older than 50 with vascular risk factors and a pupillary sparing lesion can be managed expectantly, as the risk of an angiogram outweighs the benefit.