Dermatitis Flashcards
What are the two phases of dermatitis?
Acute and chronic
State the features of the acute phase
- papulovesciular
- erythematous lesions
- oedema
- ooze/scale/crust
State the features of the chronic phase
- lichenification
- elevated plaques
- increased scaling
- risk of infection
What is the typical clinical sign of dermatitis?
itchy, ill defined erythematous, scaly patches
Name the different types of dermatitis
- contact allergic dermatitis
- irritant contact dermatitis
- atopic eczema
- discoid
- photosensitive
- seborrhoeric
- pampholyx
- eczema herpeticum
- lichen simplex
What is the pathology of contact allergic dermatitis on first exposure?
Type 4 hypersensitivity reaction where langerhans cells in the epidermis process an antigen and bind the antigen to MHC class II this cell travels to the lymph nodes to activate T cells - T cells then release cytokines which active macrophage leading to proliferation of allergen specific memory T cells
What happens on future exposure in contact allergic dermatitis?
T cells migrate to the site and cause inflammation
How is contact allergic dermatitis diagnosed?
Delayed hypersensitivity using patch test
How is contact allergic dermatitis treated?
Identify and avoid allergen
Steroids may be used to treat a flare
What is irritant contact dermatitis?
Non-specific physical irritation as a result of toxic effect of an irritant, strips the oils off the hand leading to symptoms
What are common irritants that cause ICD?
Soap, oil cleaning products
Where does ICD commonly occur?
Hands and finger web spaces
What is meant by atopic?
Word used to describe a group of diseases (asthma, eczema, hay fever and food allergy), that result from a tendency to develop hypersensitivity to allergens
What causes atopic diseases?
Genetic predisposition in addition to environmental factors
Describe the pathogenesis of acute atopic eczema
TH2 cells are activated by the presentation of antigens by langerhans cells to CD4+ cells in the dermis. TH2 cells release interleukin 4, 5, & 13 which recruit B cells and eosinophils. The B cells make IgE leading to mast cell degranulation.
Describe the pathogenesis of chronic atopic eczema
Eosinophils release IL-12 activating TH1 leading to the release of IFN alpha by CD4 and CD8 T cells
Most cases of atopic eczema have unknown aetiology but what may some be due to?
Mutations in the filaggrin gene which leads to a deficiency and thus a leaky skin barrier which allows excess water loss and dry skin
What are the symptoms of atopic eczema?
Generalised dry skin, itch, ill defined erythema and scaling. Flexural distribution.
Which infection is common in people with eczema?
Staph aureus
State the diagnostic criteria for atopic eczema
itch plus 3 or more; visible flexural rash history of flexural rash history of atopy dry skin onset < 2years
How is atopic eczema treated?
Emollients Avoid irritants Topical steroids for flare ups Phototherapy Topical Immunosuppressants Systemic treatment Biologics
What topical immunosuppressants can be used for eczema?
Tacrolimus
Pimecrolmus
What systemic immunosuppressant can be used for eczema?
Azathioprine
In photosensitive dermatitis what is the key clinical feature that indicates this diagnosis?
Collar cut off
When does stasis dermatitis occur?
Secondary to oedema, RBC extravasation, hydrostatic pressure - Vascular disease
What is the seborrhoeic dermatitis?
Cradle cap
What is pampholyx dermatitis?
acute, vesicles on lateral aspect of finger
What is eczema herpeticum?
monomorphic punched out lesions caused by herpes simplex
What is lichen simplex?
Response to the skin being repeatedly scratched or rubbed over a long period of time
