Lecture 28: Hypersensitivity part 2

Question 1

Why is understanding immunology important when it comes to dermatology?

Answer 1

• Immune skin disease associated with autoimmunity
• Immune skin disease associated with impaired barrier function of skin. i.e atopic dermatitis
• Skin disease associated with immunosuppression

Question 2

What are the layers of the skin?

Answer 2

Epidermis
Dermis
{blood vessels}
Subcutaneous fat

Question 3

What are the structures of the epidermis?

Answer 3

Stratum corneum
Stratum granulosum
Stratum spinosum
Stratum basale
{Melanocytes}

Question 4

Insert picture of weals

What is this skin condition and describe its presentation

Answer 4

Weals

• Intermittent, less than 24hrs, intensely itchy

Question 5

What are the types and causes of urticaria?

Answer 5

Many types and causes i.e

Presentations:

• Physical dermographism
• Angioedema

Causes:

• Food allergy
• Cold
• Cholinergic (Exercise)
• Allergic contact
• Drugs

Question 6

Describe the pathology of urticaria:

Answer 6

In the dermis mast cells (granular) release histamine and cause this presentation

Question 7

Whats happening in autoimmune urticaria?

Answer 7

Functional IgG autoantibodies are detected in 30-50% of patients with chronic urticaria and bind to IgE receptor on mast cells

Question 8

How can autoimmune urticaria be treated as last resort?

Answer 8

Ciclosporin (immunosuppressive)

• Omalizumab (monclonal antibodies that bind IgE in blood and prevent it activating receptor on mast cells)

Question 9

How do blisters develop?

Answer 9

They are complex but they develop at the dermoepidermal junction and is believed to be caused by a disruption of the junction between the keratinocyte; hemi desmosome; basement membrane

Question 10

Write some notes on bullous pemphigoid:

Answer 10

Blistering:

• An autoimmune disease due to the formation of IgG antibodies against hemidesmosomal proteins at the dermalepidermis junction

Question 11

Write some notes on epidermolysis bullosa:

Answer 11

• Gene defects in the proteins anchoring the basement membrane of the epidermis to the dermis.

Question 12

Describe the link between the cerebrovascular disease and bullous pemphigoid:

Answer 12

Theres three isoforms of the bullous pemphigoid antigen; Neural, skin and muscular form. BUT theres cross reactivity between the neural and skin isoforms

Therefore theres a strong association between bullous pemphigoid and neurological disease

Question 13

Write some notes on pemphigus vulgaris:

Answer 13

An autoimmune disease due to IgG autoantibodies against keratinocytes desmosome = superficial erosion

Question 14

Whats the treatment of pemphigus vulgaris?

Answer 14

• > Prednisone (but consider diabetes and hypertension as may ruin their control)
• > Rituximab, monoclonal antibody binding to B cells depleting them.

Question 15

Summarise pemphigus vs pemphigoid:

Answer 15

Pemphigoid: Full thickness blister, attack at dermoepidermal junction

Pemphigus: Superficial blister and erosions, attack within the epidermis

Question 16

Palpable purpura may indicate vasculitis; What investigations should be done?

Answer 16

• FBC
• Renal function
• Mid stream urine
• Skin biopsy
• Screening for many many autoantibodies ie antinuclear antibody
• Also screening for chronic active hep B

Question 17

How does Hep B lead to vasculitis?

Answer 17

Hep B results in the formation of immune complexes which lodge in vessel wall

• Initiate inflammation
• Wall damage
• Blood leaks

= Palpable purpura, Type 3 hypersensitivity

Question 18

Why do palpable purpura present as brown?

Answer 18

Heamoglobin breaks down to heamosiderin which is brown

Question 19

In what condition is the barrier function of the skin compromised? (commmon condition)

Answer 19

Atopic eczma

Question 20

Describe the pathology of atopic eczma:

Answer 20

Granular layer of the epidermis produces profilaggrin and converts it to filaggrin which acts as a natural moisturising factor

Question 21

What sort of reaction is allergic contact dermatitis?. Who are most susceptible to atopic dermatitis?

Answer 21

Type 4 hypersensitivity

Patients with atopic dermatitis are more susceptible to atopic contact dermatitis

Question 22

What is the most common form of skin cancer in NZ?

Answer 22

Squamous cell carcinoma

Question 23

Why are immunosuppressed more susceptible to skin cancer?

Answer 23

Competent immune system needed to deal with skin cancer / UV damage

Question 24

What drug reduces UV induced immunosupression?

Answer 24

Nicotinamide