Immunology

Question 1

What is hypersensitivity?

Answer 1

Objectively reproducible CF from exposure to a defined stimulus, at a dose tolerated by most people

E.g. insect sting hypersensitivity with local swelling, may get generalised urticaria/systemic symptoms (if so offer adrenaline autoinjector)

Question 2

What is allergy?

Answer 2

Hypersensitivity reaction initiated by specific immunological mechanisms

Most allergies caused by a few stimuli: inhaled (house dust mite, plant pollens, pet danger, moulds), ingested allergens (cow’s milk, soya, nuts, egg, wheat, legumes, seafood, fruits), insect sting/bite, drugs, natural rubber latex
-Some can be make non-allergenic by cooking e.g. apples

IgE mediated: most life-threatening allergies. Early phase in minutes from histamine release (urticaria, angioedema, sneezing, bronchospasm, CV shock), then may get a late response 4-6h later with nasal congestion/cough/bronchospasm (esp inhaled allergies)

Non-IgE mediated: delayed onset symptoms + more varied course e.g. coeliac disease

Question 3

What is atopy?

Answer 3

A personal/family tendency to make IgE antibodies in response to ordinary exposure to potential allergens (usually proteins)

A/w asthma, allergic rhinitis, conjunctivitis, eczema, food allergy

Question 4

Allergic rhinitis

Answer 4

May be atopic (a/w IgE) or non-atopic

Seasonal (related to grass/weed/tree pollens) or perennial (related to allergens like pets or HDM)

CF: coryza, conjunctivitis, cough-variant rhinitis from post nasal drip, chronically blocked nose (may affect sleep - behaviour + concentration)

A/w eczema, sinusitis, adenoid hypertrophy, asthma

M: non-sedating antihistamines (topical/systemic e.g. cetirizine), topical corticosteroid nose/eye drops, LTRA e.g. montelukast, nasal decongestants (no more than 10d due to rebound effect), allergen immunotherapy (limited by anaphylaxis risk)
-Don’t use systemic steroids cos of ADRs

Question 5

Atopic eczema

Answer 5

An allergic disease, impaired skin barrier function - cutaneous sensitisation to inhaled + food allergens
Egg allergy most common in eczema pts

Question 6

Food intolerance

Answer 6

Non-immunological hypersensitivity to a specific food e.g. temporary lactose intolerance causing watery stool following gastroenteritis

Question 7

Food allergy

Answer 7

Pathological immune response against a specific food protein

• usually IgE-mediated causing immediate reaction up to 2h, may be mild to severe (wheeze, stridor, abdo pain, D+V, shock)
• non-IgE mediated: hours after ingestion, usually GIT symptoms, may also have colic or eczema, sometimes get proctitis in first few weeks

Usually primary (child reacts on 1st exposure). Infants commonest are milk/peanut/egg

Secondary when cross-reaction between proteins e.g. can eat apples but then get allergy to birch tree pollens so then also allergic to apples. Usually mild e.g. itchy mouth

Ix: clinical if clear history, IgE mediated (skin prick tests + measurement of specific antibodies in blood, if negative IgE mediated allergy unlikely), non-IgE mediated is clinical (may need biopsy for eosinophilic infiltrates)
-For both, gold standard is excluding allergen under dietician supervision, then a placebo-controlled food challenge

M: avoid foods, non-sedating antihistamines (if no cardio reps sx), adrenaline IM auto injector for severe reaction.

• For CMPA/egg it often resolves in early childhood so may be able to reintroduce
• For nuts + seafood it usually persists

Question 8

Special circumstances for vaccination schedule

Answer 8

BCG if high risk of TB
Chickenpox from 1y up if sibling of immunocompromised children
Childrens flu vaccine 2-9y nasal spray

Complications: local swelling + discomfort, mild fever, malaise, mild form of disease about a week later e.g. MMR; severe things like anaphylaxis are v rare

CI: local guidelines. In acute illness with systemic features + fever postponed, fine in mild illness without fever, dont give live vaccines to immunocompromised (except MMR-most can have)

Question 9

Drug reactions

Answer 9

Do occur esp to Abx but most allergy labels aren’t actually allergies - viral illness often given Abx, but the viral nonspecific raises are v common

Question 10

Immunodeficiency

Answer 10

Primary: uncommon. Genetically determined defect in immune system. Suspect in children with severe, prolonged, unusual or recurrent infections. E.g. opportunistic pathogens, severe generalised molluscum or candida
-different types depending on part of immune system affected

Secondary: more common. Due to things like cancer, chemo, malnutrition, HIV, immunosuppressive drugs, splenectomy, nephrotic syndrome