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Path Week 2 > I - Allergy > Flashcards

I - Allergy Flashcards

1
Q

define allergy

A

immunological process that results in immediate and reproducible symptoms after exposure to an allergen

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2
Q

what type of reaction in allergy

A

type 1 hypersensitivity igE mediated

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3
Q

what is sensitisation

A

detection of specific IgE by skin prick testing or in vitro blood tests

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4
Q

does sensitisation or allergy occur more often

A

sensitisation +++

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5
Q

how does immune response to bacteria/virus/fungi differ from response to worms/venoms/proteases

A

immune reaction to worms/vemons respond to loss of tissue function, whereas bacterial immune reaction is due to response to direct pathogen

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6
Q

what are the signalling cytokines in Th2 immune response

A

IL25, IL33, TSLP

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7
Q

what are the effector cytokines in Th2 immune response

A

IL5, IL9, IL4, IL13

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8
Q

risk factor for development of IgE ABs

A

defects in skin epithelium (eczema)

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9
Q

describe pathway of Th2 immune response

A

damage epthelial cells secrete IL25/IL33 which act on tissue immune cells (DC, basophils etc)
induces Th2 cell immune response (IL4, IL5 etc)
and sensory neurons (itching)

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10
Q

when is IL4 induced in Th2 immune response

A

peptide MHC presentation to naive/memory Th2 cells

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11
Q

what causes immediate symptoms in allergy

A

release of inflamm mediators following allergen cross linking of IgE on surface of mast cells / basophils

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12
Q

what causes delayed symptoms in allergy

A

CD4 TH2 cell cytokine secretion and eosinophilic related tissue damage

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13
Q

what 4 factors promote IgE production

A

antigen dose
length of exposure
physical properties of allergen - eg assoicated w carrier proteins, linked to chitin, resistant to heat
route of exposure - resp/skin promotes IgE

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14
Q

what causes immune tolerance to food (prevent food allergy)

A

oral exposure to food
formation of anergic CD4 T cells lacking inflamm capacity to cause pathology
however they produce T reg cells that suppress tissue damage

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15
Q

what causes food allergy

A

skin / resp exposure to food, causing IgE sensitisation

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16
Q

describe the trends of the allergy epidemic

A

plateau of grass pollen / paeds asthma from 2000s ish to now
increase in red meat allergy recently

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17
Q

give 4 reasons why allergic disorders have risen over the last 150 years

A

hygiene hypothesis - decreased exposure = decreased natural immunity
increase in epithelial damaging agents due to industrialisation
loss of symbiotic relationship with bacteria
dietary changes

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18
Q

how do you diagnose allergy

A

HISTORY !!!
examination
allergen specific IgE test - eg skin prick / IgE blood test
functional allergen test

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19
Q

what allergies occur in infants

A

atopic dermatitis
food allergu

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20
Q

what allergies occur in childhood

A

asthma
allergic rhinitis

21
Q

what allergies occur in adults

A

drug
bee
occupational

22
Q

Sx of IgE allergies inc time frame

A

minutes or up to 2-4 hours post allergen exposure
angioedema, urticaria, itching, cough, SoB, sneeze, N&V, hypotension, sense of impending doom

23
Q

how many organ systems are involved in an allergy

A

at least 2

24
Q

what is a key feature of allergy that excludes allergy if its not present

A

reproducible - after EVERY exposure

25
Q

is the presence of IgE sufficient for diagnosis of allergic disease

A

NO - it is necessary for diagnosis but not diagnostic in itself

26
Q

does the result of skin prick test determine severity of reaction

A

NO

27
Q

what is involved in the skin prick test

A

expose patient to standardised solution of allergen extract through a skin prick to forearm
positive control = histamine
negative control = saline
measure size of reaction to each

28
Q

what is a positive result on skin prick test

A

wheal >3mm bigger than negative control

29
Q

3 advantages of skin prick test

A

quick (15-20 mins)
cheap
negative predictive value >95%

30
Q

3 disadvantages of skin prick test

A

requires experience to interpret
risk of anaphylaxis 1 in 3000
high false positive rate

31
Q

benefits of intradermal tests vs skin prick

A

more sensitive
can be used to follow up venom / drug allergy if negative in SPT

32
Q

cons of intradermal tests vs skin prick

A

less specific
labour intensive
greater risk of anaphylaxis

33
Q

IgE AB blood test limitations

A

can detect IgE ABs with little clinical relevance
low abundance allergen leads to reduced sensitivity
limited clinical utility

34
Q

when is component resolved diagnostics used

A

food allergy
insect allergy
guide immunotherapy

35
Q

what % of peanut allergy persists after childhood

A

80%

36
Q

what % of egg/milk allergy is outgrown

A

80%

37
Q

when should blood sensitisation tests be done

A

Hx anaphylaxis
can’t stop antihistamines
no access to SPT

38
Q

name a potential new blood biomarker for anaphyalxis

A

mast cell tryptase

39
Q

what is the gold standard for food and drug allergy Dx

A

challenge test - increasing volume of allergen ingested and response watched

40
Q

limitations of challenge tests

A

risk of anaphylaxis
difficult to interpret mild Sx
needs close medical supervision

41
Q

defining features of anaphylaxis

A

acute onset of symptoms / signs (mins to hours)
severe / life threatening ABC problems
skin and mucosal signs

42
Q

incidence of anaphylaxis

A

1.5 to 8/100,000

43
Q

age peak for anaphylaxis

A

0-4yrs

44
Q

4 mechanisms of anaphylaxis (inc type, cells and mediators)

A

IgE - mast cells/basophils - histamine/PAF
IgG - macrophages/neutrophils - histamine/PAF
complement - mast cells/macrophages - histamine/PAF
pharamcological - mast cells - leukotrienes/histamine

45
Q

how can anaphylaxis be retrospectively diagnosed

A

serial serum tyrptase at 30 mins then 24hours

46
Q

Mx of anaphylaxis

A

position - supine, legs raised
IM adrenaline
anti histamines after ABC
repeat IM adreanline & give IV fluids if no response
call for ITU help

47
Q

what 3 receptors does andrenaline act on

A

alpha 1
beta 1
beta 2

48
Q

safety netting for anaphyalxis

A

recognition of symptoms
avoidane of triggers
epi pen

Path Week 2 (18 decks)

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