multiple sclerosis ( ms ) is a chronic , autoimmune , demyelinating disease of the central nervous system ( cns ) .
presenting symptoms can vary greatly , but most commonly involve weakness , paresthesia , gait difficulty , or visual deficits .
virtually any area of the cns white matter can be involved , though this most classically involves the periventricular white matter .
brain stem involvement is common , though isolated cranial nerve palsies are rare signs in ms .
previous studies have suggested that isolated cranial nerve palsies in ms are more commonly found as presenting symptoms than as relapsing symptoms . among isolated cranial nerve palsies in ms ,
the fifth nerve is most commonly involved ( 4.8% ) , followed by the seventh nerve ( 3.7% ) , and the sixth nerve ( 1.0% ) .
thus , abducens palsy is a rare isolated ms finding , either as a presenting sign or during disease exacerbation .
patients with abducens palsy typically present with diplopia upon horizontal gaze , and examination can reveal a slow ipsilateral lateral rectus movement [ 4 , 5 ] .
ms has been implicated as the cause of unilateral abducens palsy in 49% of cases , though mri may not detect brain stem lesions in all cases .
one 2002 study investigating nontraumatic causes of sixth nerve palsies in patients 2050 years of age found ms to be the cause in 24% of cases .
in addition to ms , the differential diagnosis for an abducens nerve palsy includes mass lesions , lyme disease , viral infection , syphilis , sarcoidosis , and vascular disease . here ,
we report a patient who presented with a unilateral isolated abducens palsy as the initial sign of ms .
a 28-year - old man with a past medical history of hypertension and obesity presented to the emergency department with a 1-day history of double vision , most prominent upon left lateral gaze . the double vision resolved with covering either eye .
in addition , he had a 12-week history of paresthesia of the distal right hand and forearm , and the fifth digit of the right foot .
initial laboratory findings revealed only a mild leukocytosis ( 11.3  10/l ) and no other hematologic or electrolyte abnormalities .
several focal areas of increased t2 signal intensity were noted within the periventricular white matter of the frontal and parietal lobes , subcortical white matter of the left temporal lobe , and the left pons .
these findings likely represented multiple lesions distributed in both time and space , and , along with the patient 's clinical history and examination , were suggestive of a diagnosis of ms . the patient was admitted and started on intravenous methylprednisolone .
further workup to rule out other etiological causes of illness revealed an elevated esr of 25 mm / h , negative viral and lyme serologies , nmo igg negative and a negative ana . he was treated with methylprednisolone 500 mg intravenously for 3 days and then discharged home .
he was re - evaluated in the office 2 days after hospital discharge and had complete resolution of the cn vi palsy .
isolated nerve palsies occur in only 10.4% of patients with ms , with abducens palsy as the third most common isolated nerve palsy , occurring in 1.0% of patients with ms , behind trigeminal ( 4.8% ) and facial ( 3.7% ) .
these palsies occur most commonly at disease onset , though they can also occur during the course of the disease .
the lesion in the medial pons was enhancing and thus consistent with an active lesion , and the location was consistent with his cn vi palsy .
the sixth nerve nucleus is located in the pontine tegmentum , and a compact fiber tract bundle containing motor neurons from this nucleus runs medially towards the ventral region , where the cranial nerve exits the pons [ 3 , 8 ] .
our patient 's pontine lesion appeared to be located along the fiber tract emerging from the sixth nerve nucleus , and correlates with his diplopia .
while an mri lesion was detected clearly in this case , it should be noted that previous authors have found that mri does not always detect brain stem lesions accounting for these palsies in ms patients [ 4 , 6 ] . in any patient presenting with isolated cranial nerve palsies ,
ms must be considered within the differential diagnosis . in patients younger than 50 years of age ( as with our patient ) , infectious causes ( lyme disease , viral infections , syphilis ) , sarcoidosis , and autoimmune vasculitis should also be considered on the differential diagnosis , whereas for older patients small vessel vascular disease should be considered as well [ 7 , 8 ] . the presence of multiple presenting neurological deficits including cranial nerve palsies is suspicious for ms and should be investigated with mri . though mri may not always detect brain stem lesions responsible for cranial nerve palsies , it can reveal other white matter lesions of the cns that can aid in the diagnosis of ms , as was the case with our patient .
 while brain stem involvement in multiple sclerosis ( ms ) is relatively common , isolated cranial nerve palsies are rare , especially when they represent the initial presenting sign of a new diagnosis of ms . 
 this report describes a patient with no prior history of ms whose sole presenting sign was an isolated abducens palsy . 
 an enhancing pontine lesion was found on mri which correlated with his abducens palsy , and additional nonactive lesions on mri led to a diagnosis of ms . 
 this case demonstrates the importance of considering ms as part of the differential diagnosis of patients with isolated cranial nerve palsies . 
Introduction
Case Description
Discussion
Statement of Ethics
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