Third Cranial Nerve Palsy (CN III palsy)
🔑 Key concept
- CN
III ควบคุม:
- EOM:
MR, SR, IR, IO
- Levator
palpebrae →
eyelid
- Parasympathetic
→ pupil
constriction
- Lesion
→ ptosis +
ophthalmoplegia ± mydriasis
👁️ Clinical presentation
✔️ Classic triad
- Diplopia
(binocular)
- Ptosis
- Eye
“down & out”
- ± Mydriasis
✔️ Complete CN III palsy
- Ptosis
- eye: abduction
+ slight depression
- paralysis:
- adduction
❌
- elevation
❌
- depression
❌
- pupil:
dilated, nonreactive (ถ้ามี parasympathetic
involvement)
✔️ Partial palsy
- อาจ:
- pupil
ปกติ (pupil-sparing)
- หรือ dilated (pupil-involving)
- มี weakness บาง muscle
🔍 Classification
(high-yield)
1. Isolated vs nonisolated
|
Type |
Meaning |
|
Isolated |
ไม่มี neuro
deficit อื่น |
|
Nonisolated |
มี deficit อื่น (brainstem/orbit/cavernous sinus) |
2. Pupil involvement
|
Type |
Implication |
|
Pupil-sparing |
ischemia (common) |
|
Non–pupil-sparing |
aneurysm until proven
otherwise |
⚠️ Red flags (ต้อง rule
out aneurysm)
- Dilated
pupil (non–pupil-sparing)
- Painful
onset
- acute
onset CN III palsy
👉 risk posterior communicating artery aneurysm
🧬 Etiology (แบ่งตาม location)
🔴 1. Subarachnoid space
- Ischemic
(most common in adults)
- DM,
HT
- pupil-sparing
(80–90%)
- Aneurysm
(PComA)
- pupil
involved
- Infection
/ inflammation / tumor / trauma
🟣 2. Midbrain
(nuclear/fascicular)
- มี neuro deficit ร่วม
- contralateral
hemiparesis (Weber)
- ataxia
(Claude)
- bilateral
ptosis (nuclear lesion)
🔵 3. Cavernous sinus /
orbital apex
- CN
involvement หลายเส้น:
- CN
IV, VI
- V1 → pain/numbness
- ±
Horner
🟢 4. Orbit
- proptosis,
chemosis, optic neuropathy
👶 Pediatric note
- สาเหตุหลัก:
- congenital
- trauma
- tumor
- aneurysm พบได้น้อย
แต่ ต้อง exclude เสมอถ้ามี pupil
involvement
🧠 Clinical clues แยกสาเหตุ
|
Finding |
Suggestion |
|
Pupil-sparing + DM/HT |
ischemic |
|
Dilated pupil |
aneurysm |
|
Pain severe |
aneurysm / SAH |
|
Aberrant regeneration |
compressive lesion |
|
Multiple CN |
cavernous sinus |
❗ Important pearl
- ❌
Isolated mydriasis ≠ CN III palsy
→ ต้องคิดถึง Adie / pharmacologic ก่อน
🧪 Evaluation
🔥 Emergency situation
- acute
painful CN III palsy
👉 CT brain (look SAH) → LP if CT negative → CTA/MRA
🧠 Imaging strategy
|
Scenario |
Investigation |
|
Nonisolated |
MRI brain ± LP |
|
Pupil-involving |
MRI + MRA / CTA (urgent) |
|
Pupil-sparing + vascular risk |
observe ± MRI |
|
unclear / persistent |
MRI ± LP |
- CTA/MRA
sensitivity ~95–98% for aneurysm
👴 Special case
- อายุ >55 →
rule out Giant cell arteritis
💊 Treatment
✔️ Treat underlying cause
- Aneurysm
→ clipping /
coiling
- Ischemic
→ control risk
+ antiplatelet
- Inflammation/infection
→ specific
therapy
✔️ Symptomatic
- patch
eye (ลด diplopia)
- prism
- strabismus
surgery (chronic)
- ptosis
surgery
📈 Prognosis
- Ischemic:
ดี → recover 3–6 เดือน
- Aneurysm:
recovery variable
- Traumatic:
แย่กว่า ischemic
🧾 Clinical algorithm (จำง่าย)
1.
Confirm CN III palsy
2.
Check:
o pupil
involvement
o isolated
vs nonisolated
3.
If pupil involved → treat as aneurysm
4.
If pupil-sparing + DM/HT → observe
5.
Imaging if:
o atypical
o young
o no
risk factor
o not
improving
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