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Fig.8.3Shearingofolfactoryfibers.
DirectInjurytoAnyPartoftheSkullwithContusionorHemorrhageintotheBrain
PTAcanoccurinmild,moderate,orsevereheadinjurybecauseofcontusionstotheOBandthebrain,or
intraparenchymalbrainhemorrhage.ContusionsoftheOBandtheorbitofrontalpoleofthebrainarethe
mostcommoninjuriesassociatedwitholfactorylossinthiscategory(Fig.8.4).
32
Injuriestootherareasof
thebrain(e.g.,theanteriorpiriformcortex,amygdala,andtemporalloberegions)leadtolossofolfactory
discrimination andodor identificationbecause olfactorynerve fibers leave the OBandsynapse inall
theseareas.
33
Thereasonthatheadtraumaparticularlyaffectsthefrontalandtemporallobeisthat,during
accelerationanddeceleration,the brain slides over theroughbase of the anterior andmiddle cranial
fossae as it hits the front part of the inside of the skull (Fig. 8.5). The clue to involvement of these
cerebral regions is that memory and other areas of cognitive function, including behavior, are often
impaired.
Fig.8.4 Frontallobecontusionsassociatedwith depressedfracture.(FromJalloJ,LoftusCM.NeurotraumaandCritical CareoftheBrain.
NewYork,Stuttgart:Thieme;2009:108.)
Thefrontalandtemporallobesarethemostcommonlyinjuredregionsofthebraininheadandfacial
trauma,becausethebrainslidesovertheroughboneoftheanteriorandmiddlecranialfossae.
Fig. 8.5 Skull base viewed from above. (From Schünke et al. Thieme Atlas of Anatomy: Head and Neuroanatomy ©. Thieme; 2010.
IllustrationbyKarlWesker.)
TypicalClinicalFindings
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PostinfectiousOlfactoryDisorders
Asoutlinedabove,patientswithpostinfectiousolfactory disordersexperience,inthe firstinstance, the
usualsymptomsofthecommoncold,includingnasalcongestion,rhinorrhea,coryza,pyrexia,andgeneral
malaise. Symptoms of olfactory disturbance will become apparent as the illness progresses. Other
symptomsmayalsodevelop,suchasfacialpressure,otalgia,dentalpain,andpostnasaldrip,indicatinga
wider pictureofacute viral rhinosinusitis. A durationof10daysor moreis currentlyacceptedas the
demarcation between a viral anda bacterial etiology foracute rhinosinusitis. Unfortunately, itis only
whenalltheothersymptomshavesubsided,andthelossofolfactoryperceptionpersists,thattheproblem
becomesapparent.Patients will initiallyassume thatthesymptomwilleventuallydisappearandhence
thereisoftenadelayinpresentationtoa physician (closingthe ideal windowofopportunityforearly
intervention, ifthis does indeed exist). However,a sense ofapathy andlack ofknowledgeor interest
among many physicians encountering patients with olfactory disorders means that patients are often
dismissed,and,evenamongthosewhomakeittosecondarycare,afurtherlevelofapathypreventsmany
fromreceivingasatisfactoryassessmentoftheirproblem.
Alongwithhyposmia/anosmia,itislikelythatabouttwo-thirdsofpatientswillsufferfromparosmia
(adistortedolfactorysensation;usuallyunpleasant).Conversely,ofpatientssufferingfromparosmia,40
to80%haveaviralURTIastheprecedingcause.
17,34
Thissymptominitselfcanbecomemoredisabling
thantheactuallossofolfactoryability,withoverhalfofpatientssayingthatithasanegativeimpacton
theirqualityoflife.
17
Ahistoryforapatientpresentingwitholfactorylossfollowingthepresenceofotherupperrespiratory
tractsymptomsshouldclarifywhether the onsetofthe olfactory disturbancecoincidedwith that ofthe
other symptoms. If there is any doubt that the URTI was associated with the onset of olfactory
disturbances, consideration should be given to other potential causes, which may modify subsequent
investigations.Obviously,ifothersymptomsofrhinologicaloriginarestillpresent,thenitislikelythat
activeandcontinuingsinonasaldiseaseis present andneedstobethoroughlyevaluatedasindicatedin
Chapter7.Asignificantproblemwiththedelaybetweendevelopmentofthedisorderandpresentationto
a physicianwith aninterestinolfactionis thatpatientsoften find itdifficulttorememberthe onsetof
symptoms.Somepatientsmay,however,rememberthecoldasbeing“moresevere”thanpreviousURTIs.
Typically,patientsareagedbetween40and70yearsold,andwomenappeartobeafflictedmoreoften
than men. The highest incidence occurs in March and May, following peaks of URTI bouts in the
community.
ThedurationofolfactorydisturbancesafteraviralURTIcanvarywidely,althoughapproximatelyone-
third of patients is expected to spontaneously recover normal functionwithin 3 years. The disturbing
symptoms ofparosmia havebeenseparatelyreported to disappear in 29% of affected patientsaftera
meandurationofaboutayear.Interestingly,thepresenceofparosmiafromtheoutsetofthedisturbance
hasbeenshowninarecentstudytobelesslikelytoleadtoananosmicoutcomeinthelongterm than
parosmiathatdevelopslater.
35
AllsymptomsdisappearaftertheURTIclearsexceptthereducedolfactoryfunction.
Atleast50%ofsuffererswillalsohaveparosmia.
One-thirdofpatientsexperiencesspontaneousrecoverywithin3years.
Post-traumaticOlfactoryDisorders
Inmild-to-moderateheadinjurieswithoutfacialornasalfracturesorcerebralcomplications,complaints
ofalteredsmell ortasteareusuallynoticed earlyafterthe injury (2daysto1week).In one study, 25
patientswithpost-traumaticanosmiapresentedwithin7daysoftheheadinjury.
36
Inanotherstudy,itwas
reported that 83% ofpatientspresentedwithsmell loss immediately(1to5 days) aftertrauma,while
17%noteddeficits3weeksto4monthsafterinjury.
37
Thereasonforthesedifferencesisthattraumatic
anosmia can be associated with hospitalization, memory and cognitive impairment, and behavior
problems,ifcerebralhemorrhageorcontusionsoccur.Inaddition,hospitalizationforfracturedbonesand
otherorgancomplicationscanprolongrecoveryandrecognitionofsmellloss.Thenatureandseverityof
smellimpairmentintraumaticolfactorylossshowsstrongsimilaritiesinmanystudies.Theincidenceof
anosmiavariesfrom60to80%,withhyposmiaoccurringin20to25%.
24,38–40
Smelllossaftermildheadtraumaisrecognized1to5daysafterinjuryin85%ofcases.In17%of
injuries,smelllossmaynotberecognizedforupto3weeks,particlarlyinmoresevereheadtrauma
associatedwithmemorylossandlongerhospitalization.
Parosmia is not uncommon in post-traumatic olfactory loss. The incidence of post-traumatic parosmia
variesfrom14to35%.
23,24,41
Thesedifferencesareprobablyduetohistorytakingandthefactthatmany
patientsrecoverearlyandmaybemissed.Doestheoccurrenceofparosmiacorrelatewitholfactoryloss?
One studyfoundthat itwasmorecommoninhyposmia thananosmia.
24
Itappearstobemore common
withfrontalandtemporal lobeinjurythaninjuriestoother brainareas,occurring in45to50%ofsuch
cases.
42
Fortunatelyfromaprognosticperspective,parosmiashowsgradualspontaneousimprovementin
themajorityofcases.Inan8-yearstudy,itimprovedordisappearedin15to42%ofcases.
24
Post-traumaticparosmiaoccursin14to35%ofcases.Itismorecommoninpatientswithhyposmia
thananosmia,andgraduallyimprovesspontaneouslyinthemajorityofcases.
Investigations
Initial investigation should first involve a cursory endoscopic examination of the nose to assess two
things: presence or absence of signs of persisting sinonasal disease, such as mucosal congestion,
mucopus,polyps,oranatomicaldeviancesthatmaycontributetoongoingsymptoms;andvisualizationof
theolfactoryclefttoensurethatitisfreeofanydiseaseprocess(especiallyneoplasia,whichmayhave
beenmasqueradingasacommoncold).Oneshouldcarefullyaskaboutandlookforapostnasaldripor
clearrhinorrhea,whichcouldrepresentacerebrospinalfluidleakduetoafractureoftheanteriorcranial
skull base or adjacent ethmoid sinuses
43
; this can be confirmed through testing for β2-transferrin and
magnetic resonance (MR) cisternography. Imaging of the facial and nasal structures, sinuses, and
cribriform plate for identification of fractures and nasal airflow obstruction is best achieved via
computed tomography (CT) (without contrast). Detailed imaging ofthe brainandskull base toassess
olfactory systemstructures (OBand tracts,gyrusrectus, andmedial temporal lobe) thatare commonly
injuredinpost-traumaticanosmiaisbestachievedbyMRimaging(MRI)(Fig.8.6).
36
Adetailedolfactoryandgustatoryhistoryshouldbetakenabouttheoccurrenceandnatureofanyhead
traumaandaboutthecommoncomplaintofsecondarytasteimpairmentduetolossofflavor.Thisisvery
important because it may contribute information to the degree of post-traumatic olfactory loss and
prognosis.Tasteimpairmentmaybeaccompaniedbyweightlossordecreasedappetite.Thepresenceof
dysosmia, such as phantosmia or parosmia, should be established. Its presence can seriously impair
appetite and quality of life.
44,45
If seen by a neurologist, a detailed cognitive and neurological exam
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should be performed. There is evidence that gustatory thresholds can be decreased in post-traumatic
anosmia,andprimarytastetestingwiththresholdmeasurementsshouldbeperformed.
46
Fig.8.6Coronalviewofolfactorybulbs(arrow)andolfactorysulcus(arrowhead)onfastspin-echoT2-weightedmagneticresonanceimage.
(FromBinderD,SonneDC,FischbeinNJ.CranicalNerves:Anatomy,Pathology,Imaging.Stuttgart,NewYork:Thieme;2010:3).
Pyschophysicaltestingshouldbetheminimumstandardtoquantifythedegreeofolfactoryloss,butthe
qualitativedisordersofparosmiaandcacosmiaareverydifficulttoquantifybythesemeans.Nonetheless,
avalidatedolfactorytestshouldbeusedtorankthepatient'sdisorder(seeChapter6).Acomprehensive
test,suchasthe“Sniffin’ Sticks”,
47
allowsanaccurateassessmentofthis,butitistimeconsumingand
other testkits may be more practical iftime constraintsor otherresource limitations are present. The
choiceoftestkitmayalsobeinfluencedbyculturalconsiderationsintermsoftheodorchoicesavailable.
If timeand financial constraints dictatelimitedtesting, thenathresholdtestwill givethe mostreliable
assessmentasanindividualcomponent,ashasbeendemonstratedinatleasttwostudies.
48,49
Higher level testing, such as olfactory event-related potentials (OERPs) and chemosensory event-
related potentials (CSERPs), can be performed where facilities allow, and may serve to confirm the
severity of loss.
50–52
Typically, CSERPs will be preserved but OERPs may be absent or present
dependingonthedegreeofloss,andwilltendtoshowgoodcorrelationwithpsychophysicaltestresults
thatdistinguishhyposmiaandanosmia.
53
CSERPsmay, however,showa reducedresponse, indicating
crossover between olfactory and trigeminal processing (Fig. 8.7).
54,55
The presence of OERPs is
consideredtobeagoodprognosticsignforeventualrecovery.
56
•Apsychophysicaltestofolfactionandendoscopicexaminationofthenose,includingtheolfactory
clefts,shouldbetheminimumlevelofassessment.
•CTorMRImaybeappropriateinselectedcases,especiallywithheadinjuries.
Thoroughstandardizedsmellandtastetestingshouldbeperformedinallsymptomaticcases.OERPs
andCSERPsshouldbeconsideredinfacilitieswheretheseareavailable,toconfirmtheseverityof
theolfactoryloss.
Treatment,Prognosis,andCaseReports
PostinfectiousHyposmia
High-quality evidence to support thevarious treatment options for postinfectious hyposmia is lacking.
However,itisgenerallyacceptedthatacourseoforalsteroidsandtopicalsteroidsshouldbetriedinan
attempttopromoterecoveryofolfactoryfunction,basedononetrialthatdoesshowgoodevidence,
57
and
othercontributorystudies.
58–61
Zinc,inaconventionalform,hasprobablybeendiscounted
62
(and,infact,
haseven beenassociatedwiththedevelopmentofolfactorydisturbances
63
),but zincnanoparticlesmay
holdsomepromiseforfutureprogress.
64
Theroleoftopicalsteroidsinadditiontooralsteroidshasbeen
suggestedtobeusefulinpatientswithagoodinitialresponsetooralsteroids.
65
Severaltreatmentoptionshavebeeninvestigatedtodate,eitherspecificallyforpostinfectiouslossor
moregenerallyforSNODs.Firstα-lipoicacidwasinvestigatedonthepremisethatitsantioxidanteffects
and release of nerve growth factor would promote neuroepithelial regeneration. A study of patients
receiving 600 mgper day for anaverage of 4.5 months showed a mixed response, with a significant
overallimprovementinfunctionasjudgedbythe“Sniffin’Sticks”test.
66
However,todate,therehasbeen
no double-blind, placebo-controlled trial to confirm this, but notable findings included a decrease in
parosmiasandatendencyforyoungerpatientstofarebetterthanthoseovertheageof60years.
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Fig.8.7a–cOlfactoryevent-relatedpotentials(OERPs) andsensoryevent-relatedpotentials (SERPs).LOB,leftolfactory bulb;ROB,right
olfactory bulb; TDI, threshold, discrimination, andidentification score. (Figures courtesy of Dr. Philippe Rombaux, University of Louvain,
Brussels,Belgium.)
aPost-infectionOERPsandSERPsinanosmia.
bPost-infectiousolfactorylossOERPsandSERPsinhyposmia.
cPost-traumaticolfactorylossOERPsandSERPs.
Pentoxifyllineisanotheroralmedicationthathasbeensubjectedtoanon-randomizedcontrolledtrial.
It is a peripheral vasodilator indicated for use in peripheral vascular disease. It is a non-specific
phosphodiesterase inhibitor, andits mechanism ofaction in olfactoryloss is believed tobe duetoan
increaseintheactivationofodor-sensingcellsinthenosecausedbyanincreaseintheconcentrationof
cyclic adenosine monophosphate (cAMP). Another study to investigate its use in sudden-onset
sensorineural hearing loss provided anecdotal evidence that olfactory performance improved.
67
This
studywasactuallyforpatientsreceivinganintravenousformulation,ratherthantheoralformofthedrug.
Similarly,theophylline,anothernon-specificphosphodiesteraseinhibitor,wasevaluatedinanopentrial
of312 patients,ofwhich31%hada postinfectiousloss.
68
Unfortunately,although theyshowed a 50%
improvementusingdosesofupto800mgperday,theresultswerestratifiedbyolfactoryseverityrather
thanbycauseanditwasnotconductedasadouble-blind,randomizedcontrolledtrial.However,itisa
furtherhintthatmodifyingtheconcentrationofcAMPmayhavearoleintreatment.
69
Sodium citrate douches were investigated as a topical means of treating patients with SNODs, as
reportedbyPanagiotopoulosetalin2005.
70
Thetheoryforthistreatmentisbased onthe abilityofthe
citrateaniontoabsorbfreecalciumionsinthenasalmucuslayeroverlyingtheolfactoryneuroepithelium.
Thiswouldleadtoachangeinthecalciumiongradientbetweenthemucuslayerandthecytoplasmofthe
primary olfactory neurons,thusreducingcalciumuptakeinto thesecellsthrough cyclicnucleotidegated
channels.
71
Theresultistoprolongthedurationofodormoleculesbindingtoepithelialreceptors,thereby
prolongingthegeneratedactionpotential(i.e.,decreasing adaptationatthereceptor level).Thistheory
has also been shownto work in an animal experimental model. The study groupwas made upof 31
patients with a mixture of SNODs, of which post-infectious causes accounted for ~60%. Significant
improvementin olfactory performance was notedbetween 15 and 55 minutes after application of the
citrate douche. Improvements were seen in nearly all of the subjects both on psychophysical testing
(“Sniffin’ Sticks”) and on subjective reporting. As far as any potential pitfalls in this treatment are
concerned, nearlyhalfthe group reportednasal itching,although itwas onlya temporaryphenomenon.
Again, this study was limited in its applicability by its design and is under further investigationin a
double-blindtrialbytheauthor.Thisdoes, however,givehopeofaportablesolutiontopostinfectious
hyposmia,whichcouldpotentiallybeappliedpriortotimesofspecificolfactoryneed(suchaseating).
Caroverine,likepentoxifylline,isamedicationlicensedforuseinanotheranatomicallocationthathas
been applied to SNODs. It is an antispasmodic, currently available in some European countries as
Spasmium(PHAFAGPharma, Graz,Austria), indicatedforirritableboweldisease.AsanN-methyl-D-
aspartateantagonist,itisbelievedthatitsmechanismofactionliesinreductionoffeedbackinhibitionin
theOB.Quintetalin2002reportedaproofofconceptstudywheretheycompareditwithzincsulfate
overacourseof4weeks.Again,thiswasamixedgroupofsubjects,withpostinfectiousolfactorylosses
accountingfor38ofthe77patientsstudied.Thissubgroupappearedtoderivethemostbenefit.
72
ArecentstudyfromKoreainvestigatedtheadditionofginkgobilobatooralandtopicalsteroidsfor
postinfectiousolfactory loss andfoundthattherewasa 37%improvementinthresholdtestscores and
33%improvementinidentificationtestscores,thelatterbeingsignificantlybetterthanpatientsreceiving
steroidsalone.
58
Beyondpotentialmedicaltreatments,acupuncturehasasmallevidencebaseforhelpingpatientswith
postinfectioushyposmiaimproveolfactorytestingscores.Ventetalstudiedasmallgroupof30patients
receivingeitherweekly30-minutesessionsofacupuncturefor10weeksorVitaminBcomplexorallyfor
12weeks.
73
Smelltraininghasalsobeenshowntobeofbenefitinthesepatients,albeitsmall,andhasthe
advantageofbeingnoninvasiveandfreeofsideeffects.
74
Thisusuallyinvolvesaskingpatientstoactively
snifftwiceadayfrombottlesofeachofthefollowingodorsinturn:clove,lemon,rose,andeucalyptus.
Thisprocessshouldberepeatedforaminimumof12weeks.
75
SummaryofTreatmentOptionsforPostinfectiousHyposmia
•Oralsteroidtrialfollowedbytopicalsteroidsareafirst-linemeasure.
•Non-steroidalpharmacologicaloptions:
•Pentoxifylline
•Caroverine
•Theophylline
•Sodiumcitrate
•α-lipoicacid
•Homeopathicoptions:
•Ginkobiloba
•Acupuncture
•Smelltraining
Post-traumaticAnosmia
TreatmentofPTAcanbedividedintoacute(within30daysoftrauma)andchronic(greaterthan1month
aftertrauma).Intheacutephase,nasalcontusion,edema,orfracture,withorwithouthematomaformation,
is treated by an ear, nose, and throat physician. This treatment improves or resolves olfactory loss
primarilyasaresultofconductionblock.Iftheacutephaseresolvesandolfactorylossisstillpresent,
therehasprobablybeeninjurytotheolfactorynervecellsortheirpathwaytoorfromtheOB.
Olfactory loss due to injury of the olfactory receptors, nerves, OB, or brain can occur in any
combination inheadtrauma.Oral prednisonehasbeen tried in severalpost-traumaticanosmiastudies,
mostlyinAsiancountries.However,thesestudieshavenotincludedmatchedcontrols.Thelargeststudy
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enrolled116patientswithpost-traumaticolfactoryloss.
76
Patientswithnasaltraumaconfirmedbynasal
endoscopy were eliminated. Steroids were givena mean of10 months after theinjury(range 3 to21
months).Thesteroidsweregivenasfollows:prednisone15mgfourtimesdailyfor3days,10mgfour
times dailyfor 3 days, and 5 mg twice daily for 3 days. Meanfollow-upwas 5.5 months. Olfactory
function was measured using the phenylethylalcohol (PEA) odor detection threshold test (various
concentrationsofPEAweresniffed andcomparedwithacontrolbottlewithnoPEA);16%ofpatients
improved,and84%didnot.Inthegroupthatresponded,theimprovementoccurredinameanof1month
(range1to6.5months).Theimprovementdidnotcorrelatewithseverityoftheheadinjuryand75%of
thosewithanimprovementwereawareofit.Theconclusionofthisverylargestudysuggestedthathigh-
dose,short-termoralsteroidsmayimproveolfactoryacuitywithout anysignificantsideeffects.Further
studies with controls are needed, but in the meantime, because post-traumatic olfactory loss causes
significantimpairmentinqualityoflife,safety,andenjoymentofeating,itmaybeworthwhiletryingthis
treatment until a further, definitive study is performed. How steroids benefit olfactory loss is not
understood,buttheymaypossiblycontributetoneuralregeneration.
77
Post-traumaticanosmiarespondedtoa10-day,taperingcourseofhigh-dosesteroidswithinthefirst
10 months of treatment in 16% of cases (Asian studies only). More studies, here and in other
countries,areneededtoduplicatetheseresults.
Parosmia
Dealing withqualitative disorders is challenging, as itisdifficulttoassesstheimpact ofthisform of
dysfunction.Aspreviouslymentioned,dysosmiacanbeverydebilitatingandleadtodecreasedappetite,
weightloss,anddepression.Inlightofthis,severaltreatmentoptionshavebeenproposed,inadditionto
any findings noted above.
66
These are designed to reduce the overall functionality of the olfactory
apparatusinordertoreducethepotentialfortheodormoleculeinteractionthatresultsintheunpleasant
sensation. Optionsinclude hypertonic salinenasal drops, the continueduseoftopicaldecongestantsto
induce rhinitis medicamentosa, a nose clip (in the case of chemotherapy-induced severe parosmia
78
),
topical cocaine hydrochloride to induce anesthesia to the olfactory neurons,
79,80
gabapentin acting
centrally,
80
and,inseverecases,strippingtheolfactoryneuroepitheliumalongthecribriformplate.
81
PatientFoodEducation
Inthemajorityofpatientswitholfactoryloss,lossofflavorandenjoymentofeatingisamajorcomplaint,
oftenmoresothanthe lossofsmell.Thisleadstolossofappetite,weightlossinmost,andsecondary
depression. Fortunately, the primarytaste system (which is responsible for sensations of sweet, sour,
bitter, salty, and the savory broth flavor known as monosodium glutamate [MSG] or umami) and the
trigeminal sensory nerves (which are responsible for texture, temperature, and spice sensations) are
usually normal. This information should be pointed out to the patient. Adding small amounts of low
sodium MSG to chicken, steak, and other meats, with or without spicy condiments such as salsa,
Worcester sauce, or A1 steak sauce or equivalent, can improve enjoyment of eating by enriching the
“taste”ofthesefoods.Drinkingcoldgrapefruitororangejuice(sourandsweetarepreservedinolfactory
loss) with pulpcanincrease the enjoyment andtasteof a drink inthe place ofmilk,coffee,or water,
whichare likely to have little, no, or altered taste.Using recipes that emphasize normal tastants and
trigeminal sensory function have been very helpful in providing the same meal for the patient with
olfactoryimpairmentandtherestofthefamily.Thiscanimproveeatingenjoymentforall.
82
Education in changes infoodpreparation is the mainstay oftreatment for post-traumatic anosmia
withsecondaryimpairedflavorloss.Emphasizingsparednormaltaste(sweet,sour,bitter,salty,and
umami)andtexture,temperature,andspicerecognitionwillhelpimproveenjoymentofeating.
Prognosis
Patients with postinfectious olfactory loss, in the absence of definitive proof for a modifying agent,
between32and66%ofpatientsarelikelytorecover,thelatterbeingreported3yearsaftertheonsetof
olfactoryloss.
41,83,84
Infact,ithasbeensuggestedthatthenumberofpatientswithongoingolfactoryloss
lasting for more than 3 years is only19%, and,given that there may well be a significant number of
patientswhoexperiencespontaneousrecoverybeforeseekingmedicaladvice,theoverallfiguremaybe
smallerstill.
85
Thiscertainlyallows thetreatingphysician togivesomerayofhopetothepatient who
presentswithapostinfectiousquantitativeloss.
TheprognosisofPTAhasbeenstudiedformanyyears.Onestudyfoundthatthemajorityofpatients
whoimprovedosowithin3monthsofinjury.
32
Anotherstudyfoundthatof66patientsfollowedfrom1
monthto13yearsafterpost-traumaticolfactoryloss,36%improved,44%showednochange,and18%
worsened.Onlythreepatientsrecoverednormalolfaction.Twowerestudied10yearsaftertheinjuryand
the other had a very mild smell loss.
24
In a similar study 10 years earlier, 33% showed olfactory
improvementand27% worsened.
86
Many studies onthis subject suffer from the lack of standardized
smell tests. Also, subjective improvement has not been taken into account. In the study previously
mentionedinvolving66patients,
24
21%saidtheyimprovedbutonly13%showedsmelltestingevidence
ofimprovement. Whatwasalsointerestinginthe same studywasthat,of38 patients whoreportedno
changein their smell, 29% actually had a better score on their UPSIT smell test. Oneof the longest
follow-upstudiesof542 patientswith different causesofolfactoryloss,including106 withPTA,was
recentlypublished.
87
PatientswithPTAweretestedontwodifferentoccasionsbetween3monthsand24
yearsapart(median3years).Thetimebetweentheolfactorylossandtheonsetofthefirstsmelltestwas
amedianof44months(range1to476months).Thesecondsmelltestwasperformedatamedianof40
months (range 3 to 189 months). Of 69 patients who were totally anosmic, 44% experienced some
improvement, 4.5% improved to absolute normal, and 7% improved to age-adjusted normal. In 26
patients whowere hyposmic, 42% experienced some improvement and 27% returned to age-adjusted
normal.Thisstudyfound,most importantly,thatover time35 to50%ofpeopleimprove, reflecting the
regenerativecapabilityofthe olfactory nerve epithelium.Theoverall conclusionofthisverylong and
detailedfollow-upstudywasthatolfactoryimprovementdependsonthreemainfactors:
1. The time between the onset of post-traumatic olfactory loss and baseline smell testing directly
correlated with improvement:Thelonger the period, the better the improvement.This suggests that
greaterolfactoryimprovementoccurredrelativelysoonaftertheinjurywithsubsequentimprovement
afterthisperiodbeingveryslowornotall.
2.Theseverityofolfactorydysfunctionattheinitialtesting:Hyposmicpatientsweretwiceas likelyto
improveintothenormalrange.
3.Theageofthepatientatthetimeoftheheadinjuryandolfactoryloss:Peopleolderthan74yearshad
lessrecoveryoverallthanthoselessthan74yearsold.Thiswaslikelytobeduetoagingfactorsofthe
olfactorymucosaandocclusionoftheolfactoryforaminaofthecribriformplate,pinchingoffaxonsof
the olfactory receptor cells.
16
Also, neurodegenerative diseases such as Alzheimer disease and
ParkinsondiseasearemorecommonintheelderlyandcanalsoimpairtheOBandotherpathways.
88
Post-traumatic olfactory loss improves overall in 35 to 50% of cases over a 3-year period.
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