Neurogenic: Third-Nerve Palsy

Neurogenic: Third-Nerve Palsy

A 72-year-old man sought medical evaluation
after he awoke and was unable
to open his right eyelid (A). He denied
pain, recent trauma, and diplopia. This
patient's history included well-controlled
hypertension and hypercholesterolemia,
for which he was taking atorvastatin.
He did not have diabetes.

When his right eyelid was lifted
(here the lid is retracted and held in
place with tape), the patient immediately
noted diplopia, although the
visual acuity was normal (B). In this
primary position, the right eye was
abducted, indicating unopposed action
of the lateral rectus muscle. The
pupils appeared to be uninvolved.

During upward gaze (C), right
eye elevation was limited, which indicated
weakness of the superior rectus
muscle; limited right eye depression
in downward gaze indicated weakness
of the inferior rectus muscle
(D). Because the lateral rectus muscle
was intact, normal abduction was
noted in right gaze (E), whereas in
left gaze, weakness of the medial rectus
muscle resulted in limited right
eye adduction (F).

The oculomotor (third) cranial
nerve innervates 5 extraocular muscles—
the levator; the superior, inferior,
and medial rectus; and the inferior
oblique—and carries the parasympathetic
outflow to the ciliary ganglion
that controls pupillary constriction
and accommodation. Any mechanism
that disrupts this outflow causes a
partial or complete third-nerve palsy.

Third-nerve palsy can occur with
any underlying vasculopathic disease,
such as atherosclerosis, hypertension,
hyperlipidemia, and diabetes. Diabetic
third-nerve palsies often are associated
with periorbital pain.

The pupil is not involved in 80%
of vasculopathic third-nerve palsies,1
because the microangiopathy associated
with these vascular disease lesions
involves the vasa nervorum,
which causes infarction of the main
trunk of the nerve, but spares the
parasympathetic pupillary fibers that
run on the nerve externally and derive
their blood supply from the pial
blood vessels.2This pathology is most
common in older patients.

If the pupil is involved, strongly
suspect an aneurysm at the junction of
the posterior communicating artery
with the internal carotid artery; parasympathetic
palsy results in a dilated
pupil. Aneurysmal lesions cause as
many as 95% of painful, pupil-associated
third-nerve palsies.1


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