Friday, September 7, 2018

Question: Diabetic 3rd nerve palsy

In Diabetic 3rd nerve palsy all are seen except
A) Pupil dilation
B) Outward and downward gaze
C) Ptosis
D) Impaired pupillary reflex

Let us start with the basic.

Mnemonic for extraocular muscles nerve supply
LR6 SO4 Rest3

Lateral rectus is supplied by 6th nerve or abducence nerve and superior oblique by 4th nerve or trochlear nerve and rest all  muscles including LPS are supplied by 3rd muscle or  occulomotor nerve.

In pupillary reflex,
Afferent nerve: Optic nerve
Efferent nerve: Occulomotor nerve.

So in case of 3rd nerve palsy, we will have less or no actions of all EOM except lateral rectus and superior oblique.
So we will have downward gaze (due to superior oblique) and outward gaze (due to lateral rectus) and Ptosis (because LPS is supplied by 3rd nerve! ).
Pupillary reflex is also disturbed so option 4 is also ruled out.

Here is a trick in this question. In DM and HTN, microangiopathy is seen due to which central fibers are affected.
Central part do not contribute to pupillary reflex.
This leads to no pupil dilation. In case of surgical conditions and trauma, peripheral fibers are affected which causes impaired pupillary reflex or pupil dilation.

-Demotional bloke.

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