Wk10 - Dermatology Flashcards
3 main functions of the skin
Three main functions: Protection, Regulation and Sensation
Primary function as a barrier (physical and immunological)
- mechanical impacts
- protects and detects pressure
- detects variations in temperature,
- barrier to micro-organisms
- barrier to radiation / chemicals
Physiological regulation - body temperature via sweat, hair and changes in peripheral circulation - fluid balance via sweat and insensible loss - synthesis of Vitamin D
Network of nerve cells that detect and relay changes in the environment (heat, cold, touch, and pain)
Layers of epidermis
Stratum corneum Stratum lucidum Stratum granulosum Stratu spinosum Stratum basale
Embryology of the skin
Epidermis is derived from the ectoderm
5th week, the skin of the embryo is covered by simple cuboidal epithelium
7th week single squamous layer (periderm), and a basal layer
4th month, an intermediate layer, containing several cell layers, is interposed between the basal cells and the periderm
Early fetal period the epidermis invaded by melanoblasts, cells of the neural crest origin
Hair- 3rd month as an epidermal proliferation into dermis.
Cells of the epithelial root sheath proliferate to form a sebaceous gland bud. Sweat glands develop as downgrowths of epithelial cords into dermis.
Recognise interactions between immune system and skin and how this can manifest as skin disease
Langerhans cells are members of the dendritic family, residing in basal layers.
They specialise in antigen presentation:
- Acquire antigens in peripheral tissue and transports to lymph nodes
- Presents them to naive T cells which initiate cytokine cascade
- This initiates an adaptive immune response
Langerhans cells are also involved in microbial immunity, induction of hypersensitivites and pathogenesis of chronic inflammatory diseases of the skin
Skin allergy
- Skin irritation by nonallergenic and allergenic compounds induces - Langerhans cell migration and maturation
Langerhans cells migrate from epidermis to draining lymph nodes - Initial sensitization takes 10-14 days from initial exposure to allergen (nickel, dye, rubber etc)
- Once an individual is sensitized to a chemical, allergic contact dermatitis can then develop within hours of repeat exposure exposure
Ultraviolet effects on skin
Damaging effects of ultraviolet on skin - direct cellular damage and alterations in immunologic function. Direct effects include photoaging, DNA damage and carcinogenesis
- P53 tumour suppressor genes are mutated by DNA damage, developing melanoma and non melanoma skin cancers (UV light switches off p53)
Keratinocytes and melanocytes work together to protect cells from UV DNA damage - keratinocytes flood between cells to provide protective cover
Chronic UV exposure in humans leads eventually to loss of skin elasticity, fragility, abnormal pigmentation and hemorrhage of blood vessels. Wrinkles and premature ageing
Vitamin D and the skin
During exposure to sunlight, solar UVB photons
(290-315 nm) are absorbed by 7-dehydrocholesterol in the skin and converted to previtamin D(3)
Pre-vitamin D(3) undergoes transformation within the plasma membrane to active vitamin D(3)
During our winter there is minimal pre-vitamin D(3) production in the skin. Few foods naturally contain Vit D
Associations of vitamin D deficiency - increased risk of common cancers, autoimmune diseases, infectious diseases, and cardiovascular disease
Skin sensation - Merkel cells
Merkel cells at the base of the epidermis, respond to sustained gentle and localised pressure, assess shape /edge
Skin sensations - Meissner corpuscels
Meissner corpuscles situated immediately below epidermis and are particularly well represented on the palmar surfaces of the fingers and lips They are especially sensitive to light touch
e.g. cotton wools
Skin sensation - Ruffinis corpuscles
Ruffini’s corpuscles , situated in the dermis are receptors sensitive to deep pressure and stretching
Skin sensation - Pacinian corpuscles
Pacinian corpuscles are mechanoreceptors present in the deep dermis, sensitive to deep touch, rapid deformation of skin surface and around joints for position/proprioception
Other free nerve endings – Pain, temperature
Dermatology descriptions: Macule Papule Pustule Plaque Vesicle Bulla Ulceration
Macule - flat area of skin (different colour) Papule - raised from skin Pustule - raised and full of pus Plaque - raised, big Vesicle - small blister Bulla - large blister Erythematous - red Ulceration - epidermis has been removed, could be traumatic ulceration
Aetiology of acne
Acne is caused by:
- Keratin and thick sebum blockage of sebaceous gland
- Androgenic increased –> sebum production and viscosity
- Proprioni bacterium inflammation
- -> marked inflammation and scarring
Clinical features of acne
Papules Pustules Erythema Comedones (black heads - oxidised sebum; White heads - not oxidised (closed) Nodules Cysts Scarring
Distribution of acne vulgaris
Face
Chest
Back / Shoulders
Occassionally legs, scalp
Subtypes of acne & grading scale
Acne vulgaris:
Papulopustular (most common subtype), Nodulocystic, Comedonal
Steroid induced
Acne fulminans
Acne rosacea - mainly on face
Acne Inversus - mainly in armpits or groin (Hidradenitis suppuritiva)
Grading scale - Graded using Leeds acne grading system - Grades 1-12
Treatment options for acne
Reduce plugging through a topical retinoid or topical benzoyl peroxide
Reduce bacteria Topical antibiotics (erythromycin, clindamycin) or oral antbiotics (tetracyclines, erythromycin) - Benzoyl peroxide reduced bacterial resistance
Reduce sebum production using hormones – anti androgen ie Dianette / OCP (Change viscoity and quantity of oil produced)
Side effects
Topical agents – irritant, burning, peeling, bleaching
Oral antibiotics – gastro upset
OCP- possible DVT risk
Oral Isotretinoin is an oral retinoid for severe acne.
Dietary modification controversial
Reduced dietary/ glycaemic load eg milk, choc
Oral isotretinoin for Tx of acne
Is the only oral retinoid licensed for severe acne vulgaris
Concentrated form of vitamin A
Reduces sebum, plugging and bacteria
Remission of acne in around 80% teenagers
Standard course for 16 weeks 1mg/kg
Multiple side effects – most are trivial - Dry lips, nose bleeds, dry skin, myalgia
Serious side effects - Deranged liver function, raised lipids,
mood disturbance , teratogenicity
Pregnancy Prevention Program - Women have to be contraceptive
Pregnancy test done every 4 weeks
Expensive , consumes lots of clinical time
Eczema - Definitions & aetiology
Terms eczema and dermatitis interchangeable
Dermatitis - inflammation of the skin
Aetiology - combination of genetic, immune and reactivity to a variety of stimuli
Inflammation in eczema primarily due to inherited abnormalities in skin so called “barrier defect”.
Leads to increased permeability and reduces its antimicrobial function
An inherited abnormality in filaggrin expression considered a primary cause of disordered barrier function. Filaggrins are proteins which bind to keratin fibres in the epidermal cells (form the barrier defect).
The gene for filaggrin is on Chromosome 1 (if have genetic defect - more likely to get eczema)
Name the subtypes of eczema
Endogeneous - Atopic, Seborrhoeic, Discoid, Varicose (Venous), Pompholyx
Exogeneous - contact (allergy, irritant), Photoreaction (allergic, drug)
Atopic eczema
Itchy inflammatory skin condition
Associated with asthma, allergic rhinitis, conjunctivitis, hayfever (atopy)
High Ig-E immunoglobulin antibody levels
Genetic and immune aetiology
10-15% of infants affected
Remission occurs in 75% by 15 years
2/3 have a family history of atopy
Infant atopic eczema
Itchy Occasionally vesicular (small blisters) Often facial component Secondary infection < 50% still have eczema by 18 months occasionally aggravated by food (ie milk)
Complications of atpic eczema
Break in barrier defect - risk of infection
Bacterial infection - Staph. aureus
Viral infection - Molluscum - Viral warts - Eczema herpeticum
Tiredness
Growth reduction
Psychological impact
Management of atopic eczema
Emollients
Topical steroids (to reduce the inflammation)
Bandages (to prevent them from scratching)
Antihistamines (to try suppress itch response)
Antibiotics / anti-virals
Education for parents /child National Eczema Society
Avoidance of exacerbating factors
rarely dietary avoidance / house dust mite etc
Systemic drugs eg ciclosporin (immunosuppressive),methotrexate
Newest biologic agent IL4/13 blocker Dupilumab