Cranial Nerve Palsies -III, IV and VI

This isn’t so much an AFEM post but more of a brief review of a paper and a video.

Everyone finds neuroanatomy tough, you’re not alone. Most of it doesn’t really concern us in the ED that much. However we will have people attend or be referred with isolated III, IV and VI palsies.

If you understand the basics you can  know when to get worried and scan and admit and to relax and explain to the patient that this will likely improve with time.

First I suggest watching this video from the single best eye teaching source I’ve found. Chris Nickson found it for me of course 🙂

I also found this paper [via the only neuro blog I read] which covers the anatomy but also some advice on when to image and when not to. This is my basic summary.

In general

• a lot of isolated palsies can be observed as most are vasculopathic and will resolve
• isolated palsies in young people should cause consideration for mass. Non-vasculopathic sixth palsies are relatively high risk here
• the key point is identifying isolated. If they have headache or other signs then it’s not isolated
• temporal arteritis can be involved in all of them, as can myasthenia but there should be other signs/symptoms

III

• if motor only can usually be observed as most will be vasculopathic if the risk factors exist
• if mixed motor and pupil should be imaged
• if pupil only then think about compression

IV

• even traumatic IVs don’t need imaging for ICH (though maybe for fracture)
• head tilt is common along with pupils not at the same level
• some are congenital that have decompensated
• again the vasculopathic ones do quite well
• sub-arach space rarely involved
• isolated non-vasculopathic ones may (with caveats) be observed (unlike VI and III)

VI

• traumatic VI needs a scan
• vasculopathic can be observed
• non-vasculopathic should get scanned (they quote a 25% malignancy rate which seems awful high)
• they oddly don’t mention benign raised ICP as a cause

In the ED it’s not always as straightforward as this as the key is follow up. Depending on your access to neurology/ophthalmology will dictate how you manage them.