Lecture 18

25 October 2010

Eczema- Pathology

Definition

Classification

Prevalence

Incidence

Aetiology

Focus on atopic dermatitis

Seborrhoeic dermatitis

DEFINITION

Eczema=dermatitis=dermis or skin inflammation

Atopic dermatitis=

Atopy= increased liability to form immunoglobulin E and in the case of today’s lecture to develop atopic dermatitis

Seborrhoeic dermatitis

-skin inflammation of sebaceous (oil) glands

CLASSIFICATION

EXOGENOUS

Irritant dermatitis

Allergic contact dermatitis

Photo allergic contact dermatitis

Etc

ENDOGENOUS

Atopic dermatitis

Seborrhoeic dermatitis

Etc

PREVALENCE

Eczema

Atopic dermatitis 2-20 % OR HIGHER

Seborrhoeic dermatitis 1-3 %

INCIDENCE

ECZEMA

Atopic dermatitis 5 %

Seborrhoeic dermatitis 11 %

AETIOLOGY

Atopic eczema

Genetic background

Family background in about 70% of the cases

Control of IGE function by dominant gene on chromosome 6

Emergence of disease is polygenic and environmental

Clinically normal patients may have affected children which excludes a simple dominant inheritance

Yet both parents may be affected ruling out simple recessive inheritance

Immunological abnormalities

Immunoglobulins

80 % of patients with elevated serum IgE

believed to be and IgE mediated hypersensitivity

other immunoglobulin levels are usually normal in atopic patients

Interleukins

Elevated IL-4 stimulates IgE formation

Reduced IL-1 stimulates mitosis and synthesis of lymphocytes

Abnormalities in essential fatty acid metabolism

Greater release of pro-inflammatory prostaglandins and leukotrienes from platelets and leukocytes

Depressed gamma-linolenic acid in skin-evening primrose oil use

Decreased gamma-linolenic acid (GLA) gives decreased dihomogammalinolenic acid (DGLA) which gives decreased PGE₁which gives depressed T-cell regulation which allows for increased B-cell synthesis of IgE

SEBORRHOEIC DERMATITIS (SD)

Red sharply marginated lesions having a greasy scales

Sebaceous gland-namely scalp face and upper trunk

Dandruff may be a precursor of seborrhoeic dermatitis

Pityosporum ovale – a yeast-likely causative agent-both infantile and adult

not clear how it induces inflammation and scaling

infantile

scalp (cradle cap)

trunk- nappy area

tough to distinguish from infantile atopic dermatitis

adult

scalp

-dandruff

face

trunk

in adult and infantile SD-no essential fatty acid deficiency-but essential fatty acids will as a rule generally reduce inflammation

reminder of the omega 3 and 6 pathways