Dermatology in a nutshell

Dermatology in a nutshell
Dr. A. Wong-Powell
Skin diseases are very common and about a quarter of the UK population will suffer a skin issue with symptoms of itching or pain, if not treated correctly they could lead to secondary issues affecting activities of daily living. These conditions however are rarely fatal.
Skin as we know it has 4 distinctive layers: Epidermis made of stratified epithelium arises from dividing basal keratinocytes. Starting from the basal layer (at the bottom of epidermis), the cytoskeleton is made up of keratin filaments and desmosomal proteins produced by the basal layer – giving strength and prevents shedding. In the granular layer, semipermeable skin barriers are formed by the intercellular lipid bilayers secreted by keratinocytes. In stratum corneum (cornified layer) the nuclei is lost, the tough impermeable layer is made up of various proteins. Changes in the lipid metabolism and protein expression in the outer layers allow normal shedding of keratinocytes, which also plays a role in immunity by secreting various cytokines. Melanocytes secretes melanin in the basal layer, protecting against UV irradiation. Merkel cells plays a role in sensation. Langerhans’ cells found in suprabasal layer, acts as antigen-presenting cells (APC) and contains cytokine CCR6.
The BMZ – made of complex protein structures and type IV and VII collagen, laminin, integrins and hemidesmosomal proteins. Skin fragility or blistering conditions are caused by deficiencies in these proteins.
Dermis, a matrix layer of collagen and elastin, contains blood and lymphatic vessels, muscles, nerves, appendages (sweat glands, sebaceous glands, hair follicles) and variety of immune cells.
Subcutaneous layer mainly consists of adipose tissue, nerves, and blood vessels, providing insulation and lipid storage.
History taking in dermatology is similar to that of general medicine. It is important
to establish time course, distribution of lesions, symptoms, relieving and aggravating
factors, any previous skin issues or treatments, sun exposure, diet and the usual past
medical history, family history (atopy, psoriasis), drug and allergy history etc.
Basic terminology:
Macule: flat, circumscribed non-palpable lesionPapule: small palpable, circumscribed lesion (<0.5cm)Nodule: large papule (>0.5cm)Plaque: large flat-topped, elevated, palpable lesionWeal: itchy raised ‘nettle rash’ like swelling due to dermal oedema Purpura: large macule or papule of blood in the skin which does not blanch on pressurePetechia: pin-point sized macule of blood in skinEcchymosis: large confluent area of purpura / ‘bruise’Bulla: large fluid-filled blister Vesicle: small fluid-filled blisterExcoriation: scratch mark 01. Bacterial infections
- Impetigo: highly infectious, common in children, honey crusted, spread by direct
contact, mostly Staph. Aureus, take skin swabs. Treatment: topical fusidic acid TDS
and antiseptic povidone iodine for 1 week. Oral antibiotics if extensive.
- Cellulitis: hot, tender, erythematous; infection deep in subcutaneous layer, upwards
spreading. Often unwell, high temperature, caused by streptococcus. Confirmation by
serological titres. Treatment with oral or IV (extensive) antibiotics. Identify
underlying cause, portal of entry.
- Boils (furuncles): deep-seated infection in skin, Mostly Staph., painful red
swellings, teenagers, recurrence in diabetes, immunosuppresion, large boils:
carbuncles. Treatment: oral antibiotics, sometimes incision and drainage.
02. Viral infections
- Slapped cheek syndrome/fifth disease/erythema infectiosum: parvovirus B19; mild
viral illness followed by intense erythema on cheek and reticulate erythema in limbs.
- Herpes simplex virus (HSV): HSV type 1- direct contact, droplet infection, early
childhood, once infected, cell mediated immunity, recurrent as cold sores. HSV type
2- after puberty, genital area, infections symptomatic and sexually transmitted.
Treatment: aciclovir.
- Herpes Zoster/Shingles: reactivation of varicella zoster virus (VZV) chicken pox.
Tingling, pain followed by painful blistering eruption in dermatomal distribution.
Occurs in crops, pustular, crust over, lasting 2-4 weeks, more severe in elderly.
Complications: post-herpetic neuralgia, ocular disease, motor neuropathy. Treatment:
analgesia, antibiotics (if secondary bacterial infection), aciclovir.
- Human papillomavirus (HPV): common cutaneous infection ‘viral warts’. Different
subtypes, papular lesions with coarse roughened surface, hands and feet mostly, small
black dots – bleeding points in lesion. Treatment: difficult to treat effectively, topical
keratolytc agent, cryotherapy, cautery, surgery, laser, injection.
03. Fungal infections
- Dermatophytes / ring worm: 3 main genera; Trichophyton, Microsporum,
Epidermophyton, identified by microscopy and cultures of hair, skin, nail etc. Spread
by direct contact from other humans or infected animals – use of communal showers,
swimming baths, sharing towels. Tinea corporis (body), cruris (groin), pedis (foot),
manuum (hand), capitis (scalp), unguium (nail). Treatment: antifungal creams.
- Candida albicans: yeast found in body’s flora. Acts as opportunist, taking hold in
skin when there is a warm moist environment; nappy rash or intertrigo in obese
patients. Flexural areas are red, ragged peeling edge, few small pustules. Can affect
mucosal surface of mouth or GI tract – patients taking broad spectrum antibiotics or
immunospressed: superficial white, creamy pseudomembranous plaques. Treatment:
removing underlying cause, topical antifungal creams.
04. Infestations
- Scabies: intensely itchy rash casued by mite Sarcoptes scabiei. Common in children,
young adults. Spread by prolonged close contact, sexual contact. Itchy red papules
occasionally vesicles/pustules. Web spaces of fingers and toes, flexural areas.
Pathognomonic sign: linear or curved skin burrows. Treatment: topical scabicide.
- Lice: blood sucking ectoparasites affecting scalp; head lice - pediculosis capitis,
affecting body; pediculosis corporis and affecting genitals; pubic lice – crabs,
phthiriasis pubis. Treatment: malathion, phenothrin, permethrin applications.
05. Inflammatory rashes
- Eczema: inflammation of the skin. Vesicle or bullae may appear, skin can
erythematous, dry, flaky, crusted, oedematous, itchy.
Atopic eczema: strong hereditary component, family history of atopy, asthma. High
serum IgE levels. Common areas: flexural areas; elbows, ankles, behind knees.
Treatment: avoid irritants, emollient, topical steroid if needed.
Seborrhoeic eczema: overgrowth of Pityrosporum ovale and strong immune response
leads to inflammation and scaling seborrhoeic eczema. Common in Parkinsonism and
HIV disease. Treatment: suppressive with mild steroid ointment.
Contact/irritant eczema: environmental agents. Treatment: avoidance of irritant,
protective clothing.
- Psoriasis: well demarcated, red scaly plaques, skin inflamed. Triggered by infection
(group A Strep), drugs (lithium etc), UV light, alcohol abuse, stress. Unknown
aetiology but may be T-lymphocyte driven disorder. 5% develops psoriatic arthritis.
Treatment: control than cure, emollient, topical steroids, calcipotriol.
06. Possible pre-malignant conditions
- Solar keratoses/ actinic keratoses: erythematous silver-scaly papules or patches
with a conical surface and red base on fair skinned individuals. Treatment:
cryotherapy, topical 5-fluorouracil cream.
- Bowen’s disease: intraepidermal carcinoma-in-situ rarely invasive. On exposed skin,
isolated scaly red patch or plaque looking like psoriasis. Treatment: topical 5-
fluorouracil cream, cryotherapy, curretage.
07. Malignant cutaneous tumour
- Basal cell carcinoma (BCC) / rodent ulcer: most common, relate to excessive sun
exposure, later life, exposed areas, slow growing papule or nodule which ulcerate,
pearly edged. Treatment: surgical excision.
- Squamous cell carcinoma (SCC): more aggressive than BCC, metastasize if
untreated. Relate to sun and can arise in pre-existing solar keratoses or Bowen’s or
result of chronic inflammation in lupus vulgaris. Keratotic, ill-defined nodule, may
ulcerate, grow rapidly, examine lymph nodes! Treatment: excision or radiotherapy.
- Malignant melanoma: most serious type of skin cancer as metastasis occurs early
and causes death even in young people. Related to sun exposure. Other factors:
atypical mole syndrome, giant congenital melanocytic naevi, lentigo maligna and
family history of malignant melanoma. 4 types:
Lentigo maligna melanoma – patch of lentigo maligna develops a papule or nodule
Superficial spreading malignant melanoma – large flat irregularly pigmented lesion
which grows laterally before vertical invasion.
Nodular malignant melanoma – most aggressive, rapidly growing pigmented nodule
which bleeds or ulcerate. Rarely amelanotic and can mimic pyogenic granuloma.
Acral lentiginous malignant melanoma – pigmented lesions on palm, sole or under
nail and usually present late.
Treatment: urgent wide excision of lesion, histological analysis to give Clark’s level
(depth) and Breslow thickness to predict prognosis and 5 year survival rates and
further management.
Reference: Kumar & Clarke Clinical Medicine

Source: http://www.surgicareers.co.uk/sites/default/files/study/Dermatology_in_a_Nutshell.pdf