Session 9

Question 1

What causes cystic fibrosis?

Answer 1

An autosomal recessive defect in the CFTR gene affecting exocrine glands.

Question 2

What are the clinical consequences of cystic fibrosis?

Answer 2

Defects in chloride ion transport causing mucus to become thick and dehydrated; lungs are predisposed to colonisation and infection by several different organisms.

Question 3

What organisms typically cause infection in cystic fibrosis?

Answer 3

Haemophilus influenzae, Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Aspergillus fumigatus, Mycobacteria.

Question 4

What type of Pseudomonas is often the causative organism in infections in cystic fibrosis patients?

Answer 4

Mucoid Pseudomonas aeruginosa.

Question 5

What infections often cause acute exacerbation of COPD?

Answer 5

Infections of the lungs due to S. pneumonia, H. influenzae, Moraxella catarrhalis, Ps. aeruginosa or E. coli.

Question 6

How can viral lung infections predispose COPD patients to acute exacerbation?

Answer 6

Viral infection causes inflammation which makes it easier for bacteria to colonise, bacterial infection may set in and trigger an acute exacerbation.

Question 7

How may diabetes dispose patients to infection?

Answer 7

Hyperglycaemia and acidaemia impair the humoral immunity and polymorphonuclear leukocyte and lymphocyte functions; micro- and macro-vascular disease reduces tissue perfusion so neutrophil response is lowered; neuropathy reduces sensation so areas of skin may go unnoticed.

Question 8

What ENT infections are often found in diabetic patients?

Answer 8

Malignant or necrotising otitis externa, rhinocerebral mucormyosis.

Question 9

What is the causative organism in necrotising or malignant otitis externa?

Answer 9

Pseudomonas aeruginosa

Question 10

What are usually the causative organisms in UTIs found in diabetic patients?

Answer 10

Enterobacteriaceae (e.g. E. coli) or Pseudomonas aeruginosa.

Question 11

What skin and soft tissue infections are often found in diabetics?

Answer 11

Cellulitis, folliculitis, foot ulcers and necrotising fasciitis.

Question 12

What is the typical causative organism in cellulitis?

Answer 12

Staphylococcus aureus or group A beta-haemolytic Strep. species.

Question 13

What is the typical causative organism in folliculitis?

Answer 13

Staphylococcus aureus.

Question 14

What is the typical causative organism in diabetic foot ulcers and necrotising fasciitis?

Answer 14

Usually polymicrobial due to: Staphylococcus aureus, beta-haemolytic streptococcus sp, enterobacteriaceae and several anaerobes.

Question 15

What is the sensitisation phase in a hypersensitivity reaction?

Answer 15

The first encounter with the antigen which is clinically silent.

Question 16

What is the effector phase of a hypersensitivity reaction?

Answer 16

An encounter with an antigen after the first where clinical pathology occurs on re-exposure.

Question 17

What are the features of type I hypersensitivity reactions?

Answer 17

• Allergic reactions
• Occur within 30 mins and are usually harmless
• IgE or IgM mediated

Question 18

What are the features of type II hypersensitivity reactions?

Answer 18

• Antibody mediated
• Occur in 5-12 hours
• IgG and IgM mediated
• Tissue antigens

Question 19

What are the features of type III hypersensitivity reactions?

Answer 19

• Immune complex mediated
• Occur within 3-8 hours
• IgG and IgM mediated
• Soluble antigens

Question 20

What are the features of type IV hypersensitivity reactions?q

Answer 20

• Non-antibody mediated
• Caused by environmental infectious agents and self antigens
• Occur within 24-48 hours

Question 21

Describe the hygiene hypothesis.

Answer 21

Children with an urban upbringing are more likely to develop allergies than children with a rural upbringing due to factors such as lower exposure to allergens, better sanitation, etc.

Question 22

What is clinical cross-reactivity with respect to allergies?

Answer 22

People with one allergy are more likely to be allergic to certain other allergens due to the similarity of the allergens. E.g. people with cows milk allergies are very likely to also be allergic to goats milk.

Question 23

Describe the key features of mast cells.

Answer 23

Large nucleus, little cytoplasm, many granules, found near vessels and in mucosal membranes of vessels, activated by an IgE-dependent mechanism, activation causes release of contents.

Question 24

What occurs at the first exposure of an allergen in an allergic reaction?

Answer 24

Mast cells are armed with antigens ready for a second exposure: antigen-specific IgE binds to mast cells and sensitises them to the antigen; no mast cells are activated so it is clinically silent.

Question 25

What occurs at second exposure to an allergen in an allergic reaction?

Answer 25

Antigens on the mast cell bind to allergens and cause mast cell activation; activation causes release of mast cell granule content; increased vascular permeability, vasodilation and bronchioconstriction result.

Question 26

How is an allergic reaction diagnosed?

Answer 26

By the presence of mast cell products in the blood/serum.

Question 27

Describe the cause of urticaria in allergic reaction.

Answer 27

Mast cells in the epidermis cause vasodilation and increased vascular permeability. Itchy areas surrounded by redness form.

Question 28

Describe the cause of angioedema in allergic reactions.

Answer 28

Mast cells in the deep dermis cause swelling without redness.

Question 29

What is anaphylaxis?

Answer 29

Systemic manifestation of an allergic reaction affecting at least 2 organ systems which is rapidly progressive.

Question 30

How is anaphylaxis treated?

Answer 30

IM adrenaline, monitor pulse and BP, perform ECG and oximetry.

Question 31

How can allergies be diagnosed?

Answer 31

Clinical history, blood tests for serum-specific IgE or serum mast cell tryptase/histamine, skin prick tests, challenge tests.