QUIZ20thMay2020(answersbelow)

1. Whatisthedifferencebetweenincidenceandprevalence?

2. Whatisxanthochromia?

3. Whatistheprevalenceofasymptomaticcerebralaneurysminthegeneralpopulation?

4. Whatisulnarvariance?

5. DescribeandinterpretthefollowingECG.

QUIZanswers20thMay2020

1. Whatisthedifferencebetweenincidenceandprevalence?Prevalence is the proportion of existing cases of the disease/condition in a given

populationataspecifictimewhereasincidenceisthenumberofnewcasesinagiven

populationoveraspecificperiodoftime.

2. Whatisxanthochromia?XanthochromiareferstotheyellowdiscolourationofCSFduetobilirubin.Theword

xanthochromiaisfromtheGreekxanthos(yellow)andchroma(colour).

DetectingxanthochromiaintheCSFtwelvehoursafterheadacheonsetcandiagnose

subarachnoid haemorrhage as opposed to a bloody tap. Blood in the CSF releases

oxyhaemoglobin, which is then converted into bilirubin. This process is time

dependentanditmaytakeupto12hoursforbilirubintobedetectable.Bilirubincan

thenremaindetectableformorethan2weeks.Oxyhaemoglobinisdetectablefora

fewdaysafterableedbeforeitisallconvertedtobilirubin.

Bilirubin can also be detected in the CSFwhen CSF total protein is raised orwhen

serum bilirubin is raised. This may be indicated by a raised CSF bilirubin but no

oxyhaemoglobin. Inthefirst fewdaysafterableed,oxyhaemoglobinshouldstillbe

detectable. Raised total CSF protein can occur when there is a breakdown in the

blood-brainbarrier(suchasmeningitis)andsothatishowCSFbilirubincanalsobe

detected.

Xanthochromiacanbedetectedbytwomethods.Thefirst isbyvisual inspectionof

the centrifuged sample next to a water sample and against a white background.

Secondly, and more reliably, xanthochromia is detected by spectrophotometry as

bilirubin has a very narrow absorption wavelength of 440 – 460nm.

Spectrophotometrydistinguishesbilirubinfromoxyhaemoglobin,redcells,andother

proteinsorpigmentsanddetectsverylowconcentrationsofbilirubin.

3. Whatistheprevalenceofasymptomaticcerebralaneurysminthegeneralpopulation?

Theworldwideprevalanceof cerebral aneurysms is estimated tobeapproximately

3.2%withameanageof50.

4. Whatisulnarvariance?

Ulnarvarianceistherelativelengthsofradiusandulnaatthewrist.Itismeasuredas

thedistancebetweentwoparallel linesdrawnperpendiculartothe longaxisofthe

radiusatthedistalarticularsurfaceoftheulnaandtheulnarcornerofthesigmoid

notch(orcentralreferencepoint)oftheradius.Normalmeasurementis0to2mm.

5. DescribeandinterpretthefollowingECG.

Rate Regularlyirregularat88/min

Atrialtrigemenyasincompletecompensatorypause(c/wventricular)

Pwaves UprightinIIandnormalmorphologysolikelysinusinorigin

NoPwaveprecedingtheprematurebeat,likelytobeintheQRS-T

PRinterval Normal

QRS WidewithRBBBmorphology

PathologicalqwavesV1-4

Leftaxisdeviation-60

STsegment GrosselevationV1-4(concordant)

STelevation1-2mminaVLandI

InferiorSTdepressionII,IIIandaVf

è AcuteanteriorandhighlateralSTEMIwithinferiorreciprocalchanges RBBBandleftanteriorhemiblockwithatrialtrigemeny