Rashes
A rash is a change in the skin which affects its colour, appearance or texture. It may be localised to one part of the body or be generalised. The cause of many rashes can be diagnosed on clinical inspection of the rash alone. The morphology of a rash is therefore important. Morphological terms include:
Macule – a non-raised, usually well-demarcated, coloured area of skin.
Papule – a raised, usually round, well-demarcated lesion <5 mm in diameter. It varies in colour and may become nodular, undergo transformation into a vesicle or ulcerate.
Nodule – similar to a papule but is >5 mm in diameter.
Blister – a lesion in the skin containing free fluid. Those <5 mm in diameter are termed vesicles; those >5 mm are termed bullae.
Pustule – a pus-containing raised lesion <5 mm in diameter.
Purpura – purpura describes areas of bleeding into the skin >2 mm in diameter. Petechiae are <2 mm in diameter and ecchymoses are >4 mm in diameter. They do not blanch with pressure.
Erythema – a persistent reddening of the skin due to dilatation of superficial capillaries. It may be localised or generalised.
Scales and plaques – represent an excess of keratinised epithelium in the skin.
CAUSES
Macules
Congenital
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Neurofibromatosis (multiple
cafe au lait spots)
Drug reaction
Infection
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Virus
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Non-specific viral exanthem
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Fungus (pityriasis versicolor)
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Bacterial
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common where typhoid is endemic
Neoplastic
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Lentigo maligna (Hutchinson’s melanotic freckle)
Other
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Sun damage including freckles
Papules
Congenital
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Pseudoxanthoma elasticum
Other
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Campbell de Morgan spots
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Pityriasis lichenoides chronica
Systemic illness
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Xanthomata (hyperlipidaemia)
Nodules
Infections
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Atypical infections
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(commoner where TB is endemic)
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Fish-tank and swimming pool granuloma
Systemic disease
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Sarcoidosis (lupus pernio)
Pustules
Infection
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Bacterial
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Staphylococcal infection
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Impetigo, boils, folliculitis, sycosis barbae
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Jacuzzi folliculitis (
Pseudomonas infection)
Other
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Hidradenitis suppurativa
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Dermatitis herpetiformis
Drugs
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Reaction to medications
Blisters
Infection
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Viral
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Herpes zoster (including chicken pox and shingles)
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Hand, foot and mouth disease
Systemic disease
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Dermatitis herpetiformis (coeliac disease)
Other
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Secondary to peripheral leg oedema
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Toxic epidermal necrolysis (scalded skin syndrome)
Purpura
Inherited
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Clotting disorders
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von Willebrand’s disease
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Collagen vascular disorders
Infection
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Meningococcal septicaemia
Other haematological
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Thrombocytopenia
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Immune thrombocytopenic purpura
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Paraproteinaemias
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Hypergammaglobulinaemia
Systemic illness
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Vasculitis
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Henoch–Schönlein purpura
Drugs
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Cytotoxic agents (bone marrow failure)
Other
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Increased intravascular pressure, e.g. following coughing or vomiting
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Vitamin C (scurvy) and K deficiency
Erythema
Infection
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Cellulitis, e.g. streptococcal
Traumatic
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Burns (thermal, chemical, sunburn)
Systemic disease
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Chronic liver disease (palmar erythema)
SPECIFIC ERYTHEMATOUS CONDITIONS
Erythema multiforme (‘target’ lesions)
Severe form is known as Stevens–Johnson syndrome
Erythema nodosum (raised, red, painful lesions commonly on shins)
Infection
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TB
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(commoner where TB is endemic)
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Various viral and fungal infections
Other
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Inflammatory bowel disease
Erythema chronicum migrans
Livido reticularis (fish net stocking-type rash)
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Antiphospholipid syndrome
Scales and plaques
Infection
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Fungal (e.g. pityriasis versicolor)
Systemic disease
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Reactive arthritis (keratoderma blenorrhagica)
Other
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Juvenile plantar dermatosis
HISTORY
A specific history for each condition is beyond the scope of this book and the reader is referred to a textbook of dermatology.
Important factors in the history include: duration of the rash and associated symptoms; distribution at onset and any change or spread; associated itch or pain. Determine the patient’s age, racial background, occupation, sexual orientation, drug history, family history, e.g. predisposition to psoriasis, eczema or skin cancer. Take a full medical history. Enquire about any contact with infectious diseases, e.g. measles, chicken pox. Are there any associated symptoms, e.g. joint symptoms? Is there a history of exposure to the sun? Is there any history of any allergies or exposures to irritants or cosmetics? Check carefully for diabetes or immunosuppression which might suggest a fungal infection.
EXAMINATION
The patient should be examined in good light using the naked eye initially and then a magnifying glass (or dermatoscope) to inspect the rash. Ascertain the distribution of the rash. Symmetrical rashes suggest an endogenous cause, e.g. viral; asymmetrical rashes suggest an exogenous cause, e.g. local skin irritants, nappy rash. Note the morphology of the rash, i.e. macular, papular, red and scaly. Check all sites that may be affected and complete the examination by examining the scalp, eyes, mouth, hands and feet, especially the nails, and anogenital area. Check for lymphadenopathy. Is there any associated fever?
GENERAL INVESTIGATIONS
Urinalysis
Diabetes, e.g. fungal infections.
FBC
ESR/CRP
Raised in autoimmune and inflammatory conditions.
Wood light (UV light wavelength 360 nm)
Pigmentary disease and fungal infections.
Microbiology
Swabs for bacteria, scrapings for fungi.
Patch testing
Aspiration of vesicles
Culture for bacteria, e.g. staphylococci, meningococci. PCR EM or examination for viruses, e.g. herpes simplex, herpes zoster.
Viral antibodies
Herpes simplex, herpes zoster.
HIV serology
May be positive with Kaposi’s sarcoma.
Biopsy
Confirms many suspected lesions and excludes malignancy.
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Meningococcal septicaemia is rapidly fatal if not recognised. Check with a glass that the rash does not blanch with pressure.
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Lentigo maligna (Hutchinson’s melanotic freckle) is associated with a high risk of malignant change. Referral for a biopsy is essential.
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Rapid development of a new mole or change in an existing one is highly suggestive of malignant melanoma. Urgent dermatological referral is required.
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Severe or recurrent staphylococcal, candidal or herpetic viral infections may point to an immunosuppressed state. Further investigation is essential.
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Certain conditions such as pemphigus and toxic epidermal necrolysis may lead to severe illness. Urgent referral is required.
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Stevens–Johnson syndrome is life-threatening and patients should be admitted to hospital for careful monitoring.