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PAEP Infectious Diseases > Hypersensitivity reactions > Flashcards

Hypersensitivity reactions Flashcards

1
Q

explain the A.C.I.D mnemonic for hypersensitivity rxns

A

A - type 1 rxns - allergies, anaphylaxis, asthma

C - type 2 rxns - cytotoxic, kills cells by complement and phagocytosis

I - type 3 rxn - immune complexes, floating in circulation

D - type 4 rxn - delayed, contact dermatitis, dx of TB, T1DM

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2
Q

what are the different timelines for types 1-4 rxns?

A

types 1, 2, and 3 are considered immediate hypersensitivity rxns ➔ within 24h

type 4 is a delayed hypersensitivity rxn ➔ days to weeks

  1. immediate ➔ from mins
  2. immediate ➔ 2-24h
  3. immediate ➔ under 24h
  4. delayed ➔ days to weeks
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3
Q

what immune cells/Ig are most involved in each hypersensitivity rxn?

A
  1. IgE
  2. IgM/IgG
  3. IgG to form immune complexes
  4. T cell mediated ➔ CD4 Th1 (skin), CD4 Th1 (chronic hypersensitivites - T1DM), CD8 (tissue transplant)
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4
Q

what are 3 disease examples for each hypersensitivity reaction?

A
  1. allergic asthma, allergies, anaphylaxis
  2. hemolytic anemias (autoimmune hemolytic anemia, hemolytic disease of the newborn), autoimmune diseases (Grave’s disease)
  3. lupus, post-strep glomerulonephritis, serum sickness
  4. T1DM, contact dermatitis, drug reactions
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5
Q

how would you define a type 1 hypersensitivity rxn?

A

immediate IgE mediated rxn that results in smooth muscle spasm/contraction and inflammation

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6
Q

RF for T1 hypersensitivity reactions?

A
  1. comorbidities with other atopic diseases - atopic dermatitis, allergic rhinitis, allergic dermatitis
  2. genetic predisposition
  3. environmental risk – pollution +/- hygiene hypothesis
  4. SES
  5. geographical distribution
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7
Q

what are some common triggers for T1 hypersensitivities?

A
  1. environmental: dust mites, pollen, latex, mold
  2. food: nuts, eggs, wheat/grains, shellfish, fruits
  3. drugs: antibiotics
  4. animal sources: bees, wasps, cats, insects
  5. transfusions
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8
Q

what is cross reactivity in the context of T1 hypersensitivity rxns?

A

proteins of one substance are like proteins in another so the immune system reacts to them the same

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9
Q

definition of an allergy

A

abnormal immune response to otherwise harmless environmental stimulant

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10
Q

what is the definition of hypersensitivity?

A

exaggerated or inappropriate immune responses to benign antigens that can result in damage to the host

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11
Q

explain the sensitization portion of pathophys for T1 hypersensitivity

A

first exposure to the antigen
1. antigen presented to T cells by APC
2. activated T cells stimulate B cells
3. B cells release antigen specific IgE
4. IgE binds to Fc region of mast cells and basophils, awaiting next exposure

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12
Q

explain the effect stage pathophys for T1 hypersensitivity

A

2nd exposure
1. free antigen crosslinks to IgE on mast cells and basophils
2. degranulation of cells
3. release of histamines, proteolytic enzymes, cytokines, leukotrienes, prostaglandins etc.
4. increase vascular permeability, peripheral vasodilation, and SM contraction

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13
Q

what effect does histamines have on the body?

A

results in peripheral vasodilation and vascular permeability ➔ decrease perfusion of tissues

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14
Q

what are some general s/s in a T1 hypersensitivity rxn (non-severe)?

A

dermatological:
- “wheal-and-flare” which is a skin bump and redness
- rash
- hives/urticaria
- localized erythema
- pruritis

vascular:
- edema
- angioedema – swelling just under the skin in the mucous membranes – lips, face, eyes
- tingling mouth

GI
- abdominal cramping

Resp
- rhinorrhea/rhinitis
- increase mucous secretions
- sneezing

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15
Q

how do you dx anaphylaxis? what is the criteria?

A

known allergen exposure w/ hypotension (SBP < 90 or >= 30% decrease from baseline)

OR

acute illness w/ skin or mucosal symptoms with at least one of the below
1. resp compromise (dyspnea, wheeze-bronchospasm, stridor)
2. decreased BP or associated symptom of end organ dysfunction
3. severe GI symptom (severe crampy abdo ain, repetitive vomiting)

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16
Q

what s/s are present in anaphylaxis?

A
  1. difficulty or noisy breathing
  2. angioedema - swelling on tongue/mouth/lips
  3. swelling or tightness in through
  4. wheeze or persistant cough
  5. DLOC - persistant dizziness or collpase
  6. pale and floppy (children)
  7. GI: abdo pain and vomiting
17
Q

what is the role of prostaglandin in anaphylaxis?

A

causes bronchospasm

18
Q

tell me about the possible biphasic anaphylaxis

A

immediate reaction: there is a sudden response to an allergen exposure that meets the criteria for anaphylaxis

tx the anaphylaxis but there is a return of s/s within 4-12h post immediate reaction which can last up to 24-73hrs – called the late-phase reaction

19
Q

what immune mediators are involved in the late-phase reaction of anaphylaxis

A

eosinophils, neutrophils, and lymphocytes

20
Q

what end organ results are we worried about for in a late-phase reaction?

A

additional tissue damage, swelling, erythema, cough, wheezing, and mucous secretions

21
Q

how do you dx a T1 hypersensitivity rxn? what ix to order?

A

mainly a clinical dx
- do a good medical history ➔ timing of s/s, recent ingestions/new changes/triggers, prev exposure to allergens, hx of allergens, atopy or food allergies

can consider doing
- skin prick test or intradermal injection to find a specific allergen
- serum allergen-specific IgE
- CBC with diff – may see eosinophilia
- drug provocation test – controlled administration of medication to see if there is a rxn
- inhalation challenge with specific allergen to test for airway hypersensitivity ➔ allergic asthma

22
Q

how do you treat a non-anaphylaxis T1 hypersensitivity rxn?

A
  • counsel on allergen avoidance + red flags on when to return to ED/go to ED
  • antihistamines
  • consider topical antihistamine, eye drops, nasal steroids, topical steroids
  • consider corticosteroids – max effect is after 24h

consider desensitization with allergy shots if s/s still persist with allergen avoidance ➔ stimulates production of IgG on mast cells instead of IgE (via isotype switching)
- lasts around 3Y

23
Q

how do you treat an anaphylaxis rxn?

A
  1. admit + remove offending object if possible
  2. check airway, breathing, and circulation ➔ intubate, give supplemental O2, or give fluids if indicated
  3. lay pt supine w/ elevation of lower extremities (increase bloodflow to heart) + consider atropine for bradycardia
  4. IM epinephrine – may need to be repeated every 5-15min
  5. consider adding: antihistamines (re: hives or pruritis), bronchodilators (beta-agonists/ventolin/SABA, re: bronchospasm), and steroids (re: secondary response/phase, max effect after 24h)
  6. continue pt monitoring ➔ BP, resp status, O2, urine output, cardiac (telemetry)
  7. pt education on how to use IM injector, potential late-phase reaction, potential cross-reactive allergens + allergen avoidance + follow-up with allergist/family doc
24
Q

how does epinephrine work to help in anaphylaxis

A

alpha receptors ➔ peripheral vasoconstriction to help maintain your blood pressure and heart function
beta receptors ➔ relaxes smooth muscle in the airways of your lungs to help relieve shortness of breath and wheezing

25
Q

how do T4 hypersensitivites reaction occur? pathophys?

A

CD4 pathway - skin rxns + chronic hypersensitivities

intense exposure to antigen
1. APC picks up antigen
2. presents to naive CD T cell
3. APC releases IL-12 and cytokines to induce Th1 differentiation
4. Th1 releases IFN-gamma which activates macrophages
5. cytokine release ➔ recruit more immune cells
6. inflammation of the skin w/ swelling, itchiness, and pain

CD8 pathway - organ transplant rejection
1. presents antigen from inside the cell to surface
2. releases perforin and granzymes
3. forms pores and allows granzymes to induce apoptosis
4. directly kills the cells it is reactive to in the body

26
Q

how do you tx T4 hypersensitivity reactions?

A

depends on the cause, typically its self-limiting

27
Q

what drugs commonly cause T4 hypersensitivity rxns?

A

NSAIDs, anticonvulsants, sulfa drugs, penicillins

28
Q

T3 hypersensitivity pathophys

A
  1. immune complexes - IgG and antigen
  2. circulate
  3. deposits on vasculature and tissues
  4. if large ➔ spotted and cleared by immune system
  5. if small ➔ removed by complement system
29
Q

T2 hypersensitivity pathphys

A

IgG/IgM binds to allergen ➔ activates complement ➔ chemotaxis/phagocytosis ➔ cell death/destruction

PAEP Infectious Diseases (11 decks)

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