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Ростовский Государственный Медицинский Университет

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VitaminB12.

VitaminB1(Thiamine)Deficiency.Thiaminedeficiencyismostoftenseeninthesettingofpoor nutrition(inpopulationswhosedietconsistsmainlyofriceorcerealsorinpatientswithanorexia, previousgastricbypasssurgery,hyperemesisgravidarum,orchronicalcoholabuse)andinpatientson hemodialysis.Itcausestwodistinctclinicalphenotypes:WernickeKorsakoffsyndrome(seepage380)

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andBeriberi.

Beribericanpresentinbothinfants(mainlythosewhoarebreastfedbywomenwhoarethiamine deficient)andinadults.Ithastwoforms:dryberiberi,whichischaracterizedbyasymmetriclengthdependentsensorimotorpolyneuropathy,andwetberiberi,whichincludessignsandsymptomsofcardiac involvementalongwithpolyneuropathy.Measuringwholebloodthiamineisthebesttest,buteventhishas limiteddiagnosticsensitivityandspecificity.Theerythrocytethiaminetransketolaseactivitytestis anotheroption.Dependingontheseverityofthepresentation,treatmentiswitheitherintravenous(IV)or oralthiaminesupplementation.

VitaminB1.

Paraproteinemias.Paraproteinemiasarecharacterizedbyanexcessiveamountofparaproteins(i.e., monoclonalimmunoglobulinsproducedbyaclonalpopulationofmatureBcells)intheblood.Multiple

myeloma,monoclonalgammopathyofundeterminedsignificance(MGUS)andWaldenstrom macroglobulinemiacanallcauseapolyneuropathy(usuallyduetoamyloidosis)that,exceptforthe

presenceofamonoclonalimmunoglobulinspikeintheserum,presentsclinicallynodifferentlyfromthose describedabove.

Hereditarytransthyretinamyloid(hATTR)isatypeofheritable,autosomaldominantamyloidosisdue todepositionoftransthyretinderivedfibrils(transthyretinisatransportproteinfor,amongotherthing, thyroxine).Neuropathyisoftenthepresentingsymptom(bilateralcarpaltunnelsyndromeiscommon),but spinalstenosis,bicepstendonrupture,andinvolvementofotherorgansalsooccur.Inpatientswith neuropathyinadditiontounexplainedcardiac,renal,orpulmonarydisease,hATTRisanimportant diagnosistoconsider,bothbecauseitisautosomaldominantandthuscarriesimportantgenetic repercussionsandbecausethereiseffectivetreatment.Tafamidiswasapprovedin2019;itisbelievedto

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stabilizethetransthyretinproteinandreduceformationofTTRamyloid.

POEMSsyndromestandsforpolyneuropathy,organomegaly,endocrinopathy,monoclonalprotein, andskinchanges.NotallpatientswithPOEMShaveallofthesecomponents.Thepresenceofa monoclonalplasmacelldisorderandarelativelysevereperipheralneuropathyarerequiredforthe diagnosis.POEMSneuropathybeginsasatypicaldistalsensoryneuropathy,butthisisfollowedbyan oftendebilitatingmotorneuropathythatspreadsproximally.SuspectPOEMSinapatientwithaknown paraprotein(eitherbenignormalignant),neuropathy,andanyoftheotherfeaturesofthissyndrome.

CharcotMarieToothSyndrome.Manygeneticdisorderspresentwithdistalpolyneuropathyasa prominentfeature.CharcotMarieTooth(CMT)isthemostcommonofthem.CMTencompassesagroupof progressive,hereditarysensoryandmotorneuropathiesthatareduetovariousgeneticmutations associatedwithdefectiveproductionofproteinsrequiredforfullyfunctionalperipheralnerves.

Patientstendtopresentinadolescenceorearlyadulthood.Unlikeindiabeticpolyneuropathy,motor findingsoftenpredominate.Distalextremityweakness(oftenmanifestingasclumsinessandfrequently sprainedankles)withalteredgaitandmusclewastingisthemostcommoninitialpresentation.Frankfoot dropusuallyappearslaterinthecourse.Distalsensorylossispresentbutusuallylessprominent. Characteristicfeaturesonexaminationincludehighfootarches(knownaspescavus),hammertoes,and “storklegs,”aresultofdistalmuscularatrophy.IfyoususpectCMT,alwaysaskaboutafamilyhistoryof similarcomplaints.Thediagnosiscanbeconfirmedwithelectrophysiologictestingandgeneticanalysis. Thereisnospecifictherapy.

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Pescavus,orhigharchedfoot,isacommonfeatureofCMT.

IdiopathicPolyneuropathy.Thisdisorderpresentsjustlikeanyotherdistalsensorypolyneuropathy,but withnoknowncause.Asmanyas25%ofpatientswithperipheralneuropathywilleventuallybegiven thisdiagnosis.Thegoodnewsisthattheprognosisforthesepatientsisgenerallyexcellent.Thedisease doesnotsubstantiallyprogressinmostpatients,andmotorweaknessrarelydevelops.

InflammatoryDemyelinatingPolyneuropathies(GuillainBarreSyndrome)

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TheinflammatorydemyelinatingpolyneuropathiesareclassifiedundertheeponymGuillainBarre syndrome(GBS),thenamesoftwooftheFrenchneurologistswhofirstdescribedthedisorder.Unlikethe

slowlyprogressive,predominantlysensorypolyneuropathiesdescribedabove,GBSmostoftenpresents asanacutetosubacutemonophasic,rapidlyprogressiveandpredominantlymotorpolyneuropathyor, morecorrectly,polyradiculoneuropathy,sincethedemyelinationoftenbeginsatthenerveroots.Thereare severalGBSvariants—seethelistbelow—butacuteinflammatorydemyelinating polyradiculoneuropathy(AIDP)isbyfarandawaythemostcommon,representingnearly90%ofall GBScases.

Table11.1TheManyVariantsofGBS

WeaknessPredomina nt WeaknessNOTPredominant

Acuteinflammatorypolyradiculoneuropathy(AIDP) MillerFishersyndrome(MFS) Acutemotoraxonalneuropathy(AMAN) BickerstaffEncephalitis Acutemotorandsensoryaxonalneuropathy(AMSAN) Acutepandysautonomia Pharyngealcervicalbrachialvariant Puresensoryneuropathy

AcuteInflammatoryDemyelinatingPolyradiculoneuropathy.Thisiswhatmostpeoplemeanwhenthey talkaboutGBS.AIDPisanacuteonset,monophasicillnessthatprogressesrapidlyoverthecourseof severaldays.Molecularmimicryisthoughttobethepathophysiologicalmechanisminwhich,prompted byapriorinfection,crossreactiveantibodiesmistakenlyattackthemyelinofperipheralnerves.

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TheimmunesystemattacksthemyelinliningofperipheralnervesinAIDP.

Symptoms.Symptomsarefrequentlyprecededbyarespiratoryorgastrointestinalillness (Campylobacterjejuniisthemostcommonlyidentifiedprecipitant,butalonglistofviralinfections, includingEpsteinBarrvirus,cytomegalovirus,influenza,andtheZikavirus,andbacterialinfections, includingEscherichiacoliandmycoplasma,havealsobeenimplicated).

Commonsymptomsinclude:

Mildparesthesiasinthehandsandfeet(oftentheinitialsymptom) Progressive, relativelysymmetricweakness that beginsinthelower extremitiesandascendsover hourstodays;thisascendingparalysisisthemostcharacteristicfeatureofAIDP Depressedorabsentreflexes Backandlegpain,duetonerverootinflammation Oculomotor,facial,andoropharyngealweakness,duetocranialnerveinvolvement Respiratorymuscleweakness(10%to30%ofpatientsultimatelyrequireventilatorysupport)

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Autonomic dysfunction, causing labile swings in heart rate, blood pressure, and potentially dangerouscardiacarrhythmias

Box11.3CantheFluVaccineCauseGBS?

If,andthisisaverybigif,thefluvaccinecancauseGBS,theriskisextremelylow,atmost 1to2casesper1milliondoses.Thisriskisfarlessthantherisksassociatedwithinfluenza itself(allyouhavetoknowisthat61,000flurelateddeathsoccurredintheUnitedStatesin 2017–2018,whichwasatypicalfluseason).Nevertheless,itisrecommendedthattheflu vaccinenotbegiventopersonswhodevelopedGBSwithin6weeksofapriorflu vaccination.

Diagnosis.Diagnosisisdependenton(1)physicalexamination,whichshouldconfirmprofound,distal weaknesswithabsentordepressedreflexes,and(2)CSFanalysis,whichwillrevealanelevatedprotein andnormalwhitecount(knownas“albuminocytologicdissociation”).Electrophysiologictestingcanbe valuableforconfirmingthediagnosisanddistinguishingamongthedifferentGBSvariants,whichis importantlargelyforestablishingthepatient’sprognosis.Itcantakeabout3weekstoseechangeson electromyography(EMG)andnerveconductionstudies(NCS);ifdonetooearly,thesetestswillappear normal.SpinalMRIcanbenormalorshowenhancementoftheinvolvednerveroots.Itisoftennecessary toruleoutotherspinalcordpathologythatmaybemimickingGBS.Itisalsoagoodideatoorderthe basicperipheralneuropathybloodworktodefinitivelyexcludeothertreatablecauses.

Treatment.IVimmunoglobulin(IVIG)andplasmaexchange(PLEX)areequallyeffectivefirstline treatmentoptions.Combiningthemdoesnotimproveoutcomes,andthereisnoevidencethat corticosteroidsarehelpful.Mostpatientsbegintoimproveby4weeks,and80%to90%willmakeafull recovery,althoughitmaytakemanymonths.Mortalityis5%,almostalwaysfromrespiratoryfailure. Somepatientsmaysufferrelapses,andtheyarethensaidtohavechronicinflammatorydemyelinating polyneuropathy(seepage287).

Box11.4TickParalysis

OnediseasethatcanmimicGBS,althoughveryrare,istickparalysis.Itiscausedby neurotoxinsproducedbyanyofnumeroustickvectorsthatblockthereleaseofacetylcholine frompresynapticnerveterminals.Ticksmusthavebeenfeedingforatleast4daysto producesymptoms.Tickparalysiscanpresentinmanyways—asymmetricparalysis,facial andpharyngealweakness,ataxia—butwhenthepictureconsistsofparesthesiasand ascendingweaknessitcanmimicGBS.However,moreoftenitisasymmetric,andCSF analysiswillbenormal.Thekeytodiagnosisistolookforthetick,andthekeytotreatment istoremoveit.Mostpatientswillrecoverwithinhourstodaysuponremoval.Treatmentis otherwisesupportive.

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Thelonestartick,oneofmanytickspeciesthatcancausetickparalysis.(ModifiedfromWolfsonAB, HendeyGW,LingLJ,etal.HarwoodNuss’ClinicalPracticeofEmergencyMedicine,5thed.Wolters Kluwer,2009.)

Box11.5OtherGBSVariants

JustaquickwordonsomeimportantbutfarlesscommonGBSvariants:

 Acute motor axonal neuropathy (AMAN): An acute, axonal form of GBS, AMAN occurs mostly in Asia and tends to affect younger adults. It progresses more rapidly than AIDPbut has similar rates of recovery. It can be distinguished from AIDP by its lack of sensory involvement and its axonal pattern on electrophysiologic testing. It is oftenassociatedwiththepresenceofgangliosideantibodies(includingGM1,GD1a,and

https://t.me/med1917

GalNacGD1a). Acutemotorandsensoryneuropathy(AMSAN):AmoresevereformofAMAN,with both sensory and motor involvement. Prognosis is worse, with more protracted and oftenincompleterecovery.  Pharyngealcervicalbrachialvariant: Characterized by weakness of the pharyngeal, neck,andshoulder muscles, withassociatedswallowingdysfunction. Leg strengthand reflexesareusuallypreserved.Thinkofthisasalocalized,typicallyaxonalGBSvariant.  Miller Fisher syndrome (MFS): Classically presents with the clinical triad of ataxia, areflexia,andophthalmoplegia,althoughmanypatientswillonlyactuallydevelop2ofthe 3symptoms.GangliosideantibodiesagainstGQ1barepresentinthemajorityofcases.  Bickerstaff encephalitis: A brainstem encephalitis characterized by encephalopathy, hyperreflexia,andfeaturesofMFSincludingataxiaandophthalmoplegia.LikeMFS,itis alsoassociatedwithGQ1bantibodies. Puresensoryneuropathy:Thispresentswithsignificantsensoryataxiaandareflexia, witheitherabsentorveryminormotorinvolvement.  Acute pandysautonomia: Characterized by diffuseautonomicnerve involvement that can result in orthostatic hypotension, urinary retention, diarrhea, vomiting, decreased sweating,and pupillary abnormalities. Sensoryabnormalities anddiminishedor absent reflexesmayalsobepresent.

ChronicInflammatoryDemyelinatingPolyneuropathy.Chronicinflammatorydemyelinating polyneuropathy(CIDP)canbethoughtofasthechronicformofAIDP.Itisprimarilydistinguishedboth byitstimecourse—bydefinition,symptomsmustpersistforatleast8weeks—anditsresponsivenessto corticosteroidtreatment(AIDP,youmayrecall,isnotsteroidresponsive).Ittendstobemonophasic,with arelativelygradualonsetandevenmoregradualrecovery,butsomepatientscanpresentwitharelapsing andremittingcourse.Otherwise,CIDPcloselyresemblesAIDP,withpredominantlydistal,symmetric, ascendingmotorweaknessanddecreasedorabsentreflexes.AlbuminocytologicdissociationintheCSF isahallmarkfinding,aswithAIDP.IVIG,PLEX,orpulsehighdosecorticosteroidsarefirstlinetreatment.

ThereareseveralCIDPvariants,includingsensorypredominantandpuremotorforms,thatcanbe hardertorecognizeanddiagnose.CSFanalysisandelectrophysiologictestingarehelpful.

Box11.6ElectromyographyandNerveConductionStudies

Electromyography(EMG)andnerveconductionstudies(NCS)canhelptodistinguish peripheralnervedisordersfromprimarilymuscularonesandaxonaldisordersfrom demyelinatingones.EMGmeasurestheelectricalactivityofmuscles.NCS(whichassesses bothsensoryandmotornerves)measureshowwellandhowfastnervessendsignals.In general:

Features of axonal disorders include reduced amplitude of evoked nerve action potentials (the “SNAP,” or sensory nerve action potential, and “CMAP,’ or compound muscle action potential), as well as abnormal spontaneous activity, includingfibrillation potentialsandsharpwaves.

https://t.me/med1917

Features of demyelinating disorders include slowed conduction velocities, prolonged distallatencies,andconductionblock.

Electrodiagnostictestingisoftenmostusefulwhenthediagnosisisuncertain.

PerforminganEMGinvolvestheinsertionofatinyneedleintodifferentmuscles.

SmallFiberNeuropathy

Smallfiberneuropathyaffectsthesmallunmyelinatednervefibers(knownas“C”fibers)thattransmit painandtemperaturesensation.Patientstypicallypresentwithdistalburningpainandnumbness involvingthehandsandfeet.Neurologicexaminationisvariable:youmayfindalengthdependent decreaseinpinpricksensation,reducedanklejerkreflexesor,notuncommonly,noobjective abnormalitiesatall.Associatedautonomicsymptomsarecommonandcanincludedrymouth,urinaryand bowelretention,andorthostatichypotension.Diabetesisbyfarthemostcommonunderlyingetiology,but thelistofpotentialcausesislongandincludes:

VitaminB12(cobalamin)deficiency VitaminB6(pyridoxine)toxicity Infectiousetiologies(HIV,hepatitisC) Autoimmuneconditions(Sjogrensyndrome,sarcoidosis,systemiclupuserythematosus) Paraproteinemias(multiplemyeloma) Paraneoplasticdisorders

https://t.me/med1917

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