cranial nerve III palsy; oculomotor nerve palsy

Etiology: 1) ischemic microvascular disease a) diabetes mellitus b) hypertension 2) aneurysm of the posterior communicating artery 3) cavernous sinus thrombosis (may also involve CN4 & CN6) 4) myasthenia gravis 5) Grave's disease 6) tumor 7) trauma Pathology: 1) diabetic 3rd nerve palsy a) pupillary sparing due to vascular damage in the central portion of CN-3 b) parasympathetic pupillomotor fibers at the periphery remain intact 2) aneurysm of the posterior communicating artery a) may also spare parasympathetic pupillomotor fibers at the periphery of CN-3 b) compression of CN-3 as in emerges from the brainstem at the junction of the posterior communicating artery & the internal carotid artery Clinical manifestations: 1) diabetic 3rd nerve palsy a) pain often precedes palsy b) mild ptosis of affected eye c) inability to adduct or move affected eye medially d) pupillary reflexes are often intact 2) myasthenia gravis a) disturbance in CN-IV & CN-VI are also likely b) internuclear ophthalmoplegia & other sign of myasthenia gravis Laboratory: 1) serum chemistries: serum glucose 2) erythrocyte sedimentation rate (ESR) Special laboratory: -> tensilon test (myasthenia gravis) Radiology: 1) magnetic resonance imaging (MRI) 2) cerebral angiography if pupil(s) involved & MRI is negative Differential diagnosis: 1) myasthenia gravis 2) thyroid disease (hyperthyroidism) 3) orbital pseudotumor (inflammatory) 4) Parinaud's syndrome 5) giant cell arteritis 6) cavernous sinus thrombosis may also involve cranial nerve 4 & cranial nerve 6 - Tolosa Hunt syndrome Management: 1) total cranial nerve 3 palsy with normal pupil a) follow patient for 5 days - after 5 days, pupil is unlikely to dilate b) identify risk factors (diabetes, HTN) c) recovery generally occurs < 3 months 2) total cranial nerve 3 palsy with dilated pupil* a) MRI immediately to rule out compressive lesion b) if MRI is negative, cerebral angiography 3) partial cranial nerve 3 palsy with normal pupil - follow without treatment 4) partial cranial nerve 3 palsy with dilated pupil* a) MRI immediately to rule out compressive lesion b) if MRI is negative, cerebral angiography * key to management is the presence of a dilated pupil

References

Medical Knowledge Self Assessment Program (MKSAP) 11, American College of Physicians, Philadelphia 1998