Psoriasis

Psoriasis is a relatively common disorder affecting 1–2% of the population. Classically it presents with red, raised, scaly patches or plaques, which reflect increased keratinocyte proliferation within the epidermis, associated with an inflammatory cell infiltrate (including polymorph microabscesses). There is also increased vascularity within the upper dermis.

The aetiology of psoriasis remains relatively poorly understood. Although there is clearly a genetic component, with younger patients in particular often reporting a positive family history, patterns of inheritance vary and further studies are ongoing to try to understand which genetic factors are at play. In addition, it remains unclear why some areas of skin are affected, but others remain normal in the face of an underlying genetic predisposition. Triggers that can be associated with the development of/flare-up of psoriasis in susceptible individuals include infections and trauma, and possibly stress, although the latter is contested by some dermatologists.

Clinical Presentation

Several different patterns of psoriasis are recognised, some of which are common, while others are only rarely seen. The key clinical features of each subtype are shown in Table 19.1 and Plates 19.1–19.4.

Table 19.1 Clinical Features and Specific Treatments for Different Types of Psoriasis

Psoriatic Arthropathy

Arthropathy occurs in 5–10% of patients with psoriasis and may take one of several forms:

• predominant distal interphalangeal joint involvement
  
• symmetric polyarthritis (seronegative rheumatoid-like changes)
  
• asymmetric oligo/pauciarticular arthritis
  
• spondylitis (± sacro-ileitis) with stiffness in the back/neck; HLA B27 positive
  
• arthritis mutilans, a severe deforming destructive arthritis.

Nail changes are common in patients with psoriatic arthropathy, but not all cases are associated with skin disease.

Treatment

Topical Agents

• Emollients help to control scaling.
  
• Salicylic acid reduces hyperkeratotic, scaling lesions; often used in combination with coal tar, dithranol or topical corticosteroids.
  
• (Coal) tar is effective but unpleasant to use; typically reserved for scalp involvement; sometimes used in combination with ultraviolet (UV) radiation therapy (see below).
  
• Dithranol is effective for chronic plaque psoriasis; applied directly to lesions (may be covered with a dressing) and left for up to an hour (occasionally longer, but only under supervision); dithranol is irritant (start with 0.1% and gradually increase as required/tolerated) and stains skin, hair and bedding/clothes brown; avoid use on the face or in flexures; may be combined with tar and UV radiation.
  
• Topical corticosteroids may suppress (although not erradicate) lesions (e.g. scalp, flexures), but should be used with care (risk of precipitating brittle or erythrodermic psoriasis) (Table 19.1).
  
• Vitamin D analogues (e.g. calcipotriol, tacalcitol) and activated vitamin D (e.g. calcitriol) are useful in mild to moderate psoriasis; serum calcium levels must be monitored in those using larger doses.
  
• Tazarotene is a retinoid; irritant, especially if applied to normal skin.

Phototherapy

• UVB radiation is effective in the treatment of chronic stable psoriasis and guttate psoriasis, especially when topical agents have proved ineffective; must be used with care due to risk of sunburn; typically given as short courses, e.g. 2–3 times per week until clearance is achieved; combination with coal tar, dithranol or vitamin D analogues increases efficacy.
  
• Photochemotherapy (psoralens and ultraviolet A phototherapy (PUVA)). Psoralens (given either by mouth or topically) enhance the effect of UV radiation; treatment is typically given twice weekly, and protective glasses are required to avoid ocular damage. Higher cumulative doses exaggerate skin ageing and are associated with an increased risk of keratoses and neoplastic lesions (especially squamous carcinoma).

Systemic Therapy

• Methotrexate. Once weekly dosing, together with folic acid; effective in severe psoriasis refractive to topical therapy; patients should be advised of potential adverse effects including myelosuppression (sore throat, mouth ulceration, easy bruising), hepatotoxicity (nausea/vomiting, abdominal pain, dark urine), respiratory effects (shortness of breath), inhibition of spermatogenesis and teratogenicity (effective contraceptive measures must be in place before treatment is commenced).
  
• Retinoids (e.g. acitretin) are reserved for severe, resistant psoriasis. Side effects include dryness and cracking of skin and lips, epistaxis, transient hair loss, myalgia, hepatotoxicity, hyperlipidaemia and teratogenicity (effective contraceptive measures must be in place before treatment is commenced).
  
• Ciclosporin (cyclosporin) is effective even in very severe psoriasis; nephrotoxic and requires close monitoring of renal function, especially in the early stages of treatment; avoid concomitant UVB/PUVA therapy.
  
• Biological agents. Anti-TNFα therapies (e.g. etanercept, adalimumab, infliximab) may be used in very severe plaque psoriasis that has failed to respond to systemic treatments and to photo(chemo)therapy, or in cases where standard treatments are not tolerated/contraindicated. Ustekinumab (a monoclonal antibody that targets interleukins 12 and 23) has also shown benefit.
  
• Systemic corticosteroids. Only rarely indicated and must be given under expert supervision.

Table 19.1 shows preferred treatment options for each subtype of psoriasis. Psoriatic arthropathy often responds to simple anti-inflammatory agents. In more severe cases, methotrexate or biological agents can be tried.

Eczema/Dermatitis

In acute eczema the skin is erythematous and oedematous, with papules/vesicles and weeping (i.e. ‘boiling over’). In chronic eczema, oedema is absent and the epidermis becomes thickened/hyperplastic, with exaggeration of the skin markings (so-called lichenification) (Plate 19.6). Itching may be the dominant symptom. Secondary infection is common: bacterial (commonly staphylococcal) or viral (herpes simplex). Healed lesions do not scar, but may pigment.

Secondary spread to involve other areas is a well-recognised phenomenon of acute eczema and may even involve areas that have not been directly exposed to a particular allergen in cases of contact dermatitis. Rarely, the whole of the body may be affected by a generalised exfoliative dermatitis.

Several different patterns of eczema are recognised; the key clinical features of each subtype are shown in Table 19.2 and Plates 19.5–19.7.

Table 19.2 Causes, Clinical Features and Specific Treatments for Different Types of Eczema (Dermatitis)

Treatment

Wherever possible, the local irritant or sensitiser should be removed. Many commercial soaps contain such irritants and washing with water ± soap substitutes is advised. If the lesion is weeping, local soaks, e.g. potassium permanganate (antiseptic and astringent) may aid healing; if dry, emollients should be applied liberally and regularly to the affected areas – bath/shower oils may further help. Continued emollient use is required even when the acute episode has subsided. Sedative antihistamines by mouth may relieve pruritus and allow sleep. Bandages (including those containing zinc and ichthammol) may be applied over topical corticosteroids (see below) or emollients to treat eczema of the limbs. Systemic antibiotics are required for secondary bacterial infections and antiviral therapy for cases complicated by herpes simplex infection. Antifungal therapy may be useful in cases of seborrhoeic dermatitis where the yeast Malassezia is implicated.

Topical corticosteroids remain the mainstay of treatment for most patients with eczema. The potency of the corticosteroid should be appropriate for the site and severity of the condition, e.g. weaker preparations are preferred for the face and on flexures, while more potent preparations may be required on the limbs/trunk, especially if there is associated lichenification.

In more severe/refractory cases immunomodulatory agents can be tried, including topical tacrolimus or pimecrolimus and oral ciclosporin. The oral retinoid alitretinoin is also licensed for the treament of severe chronic hand eczema refractory to potent topical corticosteroids (cautions and adverse effects are similar to those of other retinoid preparations; pregnancy must be excluded and effective contraception practised).

Table 19.2 shows preferred treatment options for each subtype of eczema.

Acne Vulgaris

Rosacea

Hidradenitis Suppurativa

Bacterial, Viral, Fungal and Parasitic Skin Infections

A number of different organisms are capable of causing primary cutaneous infections/infestations. The more commonly encountered pathogens and their associated clinical sequelae are shown in Tables 19.3–19.6 and Plate 19.8.

Table 19.3 Bacterial Infections Involving the Skin.

Table 19.4 Viral Infections Involving the Skin.

Table 19.5 Fungal Infections Involving the Skin.

Table 19.6 Parasitic Infections Involving the Skin.

Cutaneous Drug Reactions

Table 19.7 show the different types of eruption that may be encountered. Drugs that are particularly prone to causing cutaneous reactions include antibiotics (e.g. sulphonamides, penicillins – although not all patients who state they are ‘penicillin allergic’ are truly allergic!), NSAIDs and hypnotics/tranquillisers.

Table 19.7 Patterns of Cutaneous Drug Reactions

Key features of the major types of drug reaction are described below.

Clinical Features/Causative Agents

Exanthematous Eruptions

• variable speed of onset – typically starts within the first few days of treatment, but may develop more quickly (e.g. within hours of exposure) or appearance may be delayed (e.g. several weeks, making the link more difficult to establish)
  
• usually widespread, symmetrical, erythematous maculopapular rash, often resembling a viral exanthem (Plate 19.9)
  
• itchy
  
• examples: penicillins, sulphonamides, NSAIDs

Urticaria and Anaphylaxis

• secondary either to direct effect on mast cells or type I or type III hypersensitivity reaction
  
• eruption usually occurs 3–7 days after therapy is started
  
• rarely, rapid onset anaphylactic reactions (with fever, wheezing, arthralgia and hypotension) occur and are potentially fatal if not rapidly recognised and treated
  
• examples: penicillins, cephalosporins, aspirin, opioids, certain vaccines

Eczema

• type IV hypersensitivity reaction
  
• typically in response to a topical agent
  
• examples: lanolin, preservatives, topical antibiotics (especially aminoglycosides), topical antihistamines, topical local anaesthetics (although not lignocaine), topical corticosteroids

Exfoliative Dermatitis (Erythroderma)

• widespread reddening/inflammation of the skin ± scaling
  
• in more severe cases may be associated with loss of temperature regulation, dehydration, superadded infection, hyperdynamic circulation (± cardiac failure in the elderly)
  
• examples: phenytoin, sulphonylureas, sulphonamides, allopurinol, gold, barbiturates

Fixed Drug Eruptions

• typically manifests as a circular/oval patch of erythema with central purple discolouration ± bullous change
  
• single or multiple sites
  
• often initially misdiagnosed as ringworm infection
  
• usually affects the same area(s) of skin each time the patient is exposed to the offending drug
  
• postinflammatory pigmentation
  
• examples: phenolphthalein-containing laxatives, tetracyclines, sulphonamides, dapsone

Vasculitis (p. 284)

• typically a cutaneous small vessel vasculitis (leukocytoclastic vasculitis)
  
• numerous palpable, purpuric lesions (often on the lower limbs); occasionally developing into haemorrhagic vesicles/bullae
  
• may be associated with systemic involvement (e.g. renal)
  
• examples: thiazide diuretics, cimetidine, sulphonamides

Erythema Multiforme (Plate 19.10)

• target lesions
  
• examples: sulphonamides, cotrimoxazole, rifampicin, barbiturates

Erythema Nodosum

• tender, red, raised lesions (Plate 19.11)
  
• typically on the shins, but may also affect upper limbs
  
• examples: sulphonamides, salicylates

Pigmentary Changes

• various drugs can be associated with different pigmentary skin changes
  
• examples: blue-black (chloroquine, amiodarone (in sun-exposed areas)); brown (oestrogens = chloasma)

Bullous/Blistering Reactions

• may be seen in the context of a fixed drug eruption or with drug-induced pemphigus, pemphigoid or porphyria cutanea tarda

Photosensitivity

• direct phototoxic effect or exacerbation of a pre-existing condition
  
• in phototoxic reactions, the dose of the drug and the degree of ultraviolet radiation exposure determine the extent of the reaction; characterised by erythema, swelling ± eczematous changes
  
• examples: tetracyclines, sulphonamides, phenothiazines, thiazide diuretics

Acneiform Eruptions

• papules/pustules
  
• examples: corticosteroids, androgenic drugs, lithium

Lupus-Erythematosus-Like Syndrome

• rare
  
• examples: hydralazine, isoniazid, minocycline

Lichen Planus-Like Eruptions

• rare
  
• may be indistinguishable from idiopathic lichen planus, although eczematous/scaly changes are more common
  
• examples: antimalarials, sulphonylureas, gold, thiazide diurectics (in sun-exposed areas)

Purpura

• may be a feature of any severe drug reaction and typically results from capillary damage and/or thrombocytopenia

Management

• Wherever possible discontinue suspected offending drug.
  
• Minimise other potential provoking factors, e.g. UV radiation exposure.
  
• Oral antihistamines for urticaria.
  
• Mild topical steroids may help itching.
  
• Adrenaline (epinephrine) may be life-saving in acute hypersensitivity reactions including shock and angioedema (p. 115), and systemic steroids may be required in severe but less acute cases.

Skin Manifestations of Systemic Disease

Skin involvement in systemic disease is not uncommon and can be the presenting feature, e.g. erythema nodosum in sarcoidosis (p. 120). In some instances, several different underlying disorders can give rise to the same skin condition (Table 19.8), while other cutaneous manifestations are more specific. Some disorders (e.g. diabetes mellitus) are associated with a wide array of cutaneous features.

Table 19.8 Skin Conditions Associated with a Variety of Systemic Diseases

Infections

• haemolytic streptococcal infection – erythema nodosum (Table 19.8, Plate 19.11), erythema multiforme (Table 19.8, Plate 19.10), erythema marginatum
  
• acquired immune deficiency syndrome (AIDS) – oral/oesophageal candidiasis, ‘hairy leukoplakia’ (Epstein–Barr virus), seborrhoeic dermatitis, perianal warts, recurrent/severe herpes simplex, Kaposi’s sarcoma, lipodystrophy (in those on highly active antiretroviral therapy)
  
• Lyme disease (due to infection with the spirochaete Borrelia burgdorferi; transmitted by Ixodid tick bite) – erythema chronicum migrans

Diabetes Mellitus

Skin manifestations include:

• neuropathic and neuroischaemic ulcers
  
• xanthomata – signifying hyperlipidaemia
  
• lipohypertrophy (rarely lipoatrophy)
  
• necrobiosis lipoidica – typically occurs on the shins; intially erythematous, but becomes yellowish brown and atrophic with visible vessels beneath the skin; occasionally ulcerates (Plate 19.12)
  
• diabetic dermopathy – small brown scar-like lesions, often on the shins
  
• acanthosis nigricans – indicating the presence of severe insulin resistance (Plate 19.13)
  
• cheiroarthropathy – thickening of the skin of the hands
  
• mucosal candidiasis (e.g. balanitis, vulvovaginitis)
  
• granuloma annulare.

Endocrine Disorders

• thyrotoxicosis/hyperthyroidism – palmar erythema, alopecia; Graves’ disease is specifically associated with acropachy (digital clubbing), onycholysis, pretibial myxoedema
  
• hypothyroidism – pallor, malar flush (which together may lead to the classical ‘strawberries and cream’ appearance), thinning of scalp hair, loss of outer part of eyebrows, thickened/dry skin (myxoedema)
  
• Cushing syndrome – thinning of skin, spontaneous/easy bruising, acne, hirsutism, violaceous striae
  
• Addison’s disease – hyperpigmentation (especially palmar creases, buccal mucosa, scars); may be associated with vitiligo

Hyperlipidaemia

Both primary and secondary hyperlipidaemia may be associated with lipid deposits in the skin (xanthomata), which are yellow/orange in colour and may occur as:

• xanthelasma(ta) – eyelids
  
• tendon xanthomata – extensor tendons of the hands, Achilles tendons
  
• palmar xanthomata – creases of the palms
  
• tuberous xanthomata – over bony prominences
  
• eruptive xanthomata – crops of papules (indicative of hypertriglyceridaemia).

Rheumatological Disorders

• gout – tophaceous deposits
  
• rheumatoid arthritis – palmar erythema, rheumatoid nodules, vasculitic lesions, pyoderma gangrenosum
  
• systemic lupus erythematosus – facial erythema (‘butterfly rash’), photosensitivity, alopecia, Raynaud’s phenomenon
  
• discoid lupus erythematosus – principally affects light-exposed areas, with scaling and erythematous plaques; healed areas show scarring and hypopigmentation
  
• dermatomyositis – purple heliotrope discolouration, classically around the eyes, but may involve other areas, especially sun-exposed; periorbital oedema; vasculitic lesions in the childhood variant
  
• systemic sclerosis – tight, shiny appearance of the skin over the face, with beaked nose and restriction of mouth-opening; facial telangiectasia; sclerodactyly, digital infarcts, calcinosis, Raynaud’s phenomenon
  
• Reiter syndrome – keratoderma blennorrhagicum, buccal mucosal ulceration, circinate balanitis

Sarcoidosis

Skin manifestations include:

• erythema nodosum (Table 19.8, Plate 19.11)
  
• lupus pernio – purplish discolouration of the skin of the nose and ears
  
• papules, nodules, plaques, sarcoid granulomas.

Malignancy

Skin manifestations of malignancy include:

• cutaneous deposits, e.g. breast, bronchus, renal, ovarian (including ‘Sister Joseph’s nodule’, an umbilical metastatic nodule)
  
• generalised pruritus (associated with a wide array of systemic malignancies, especially lymphoma)
  
• acanthosis nigricans (Plate 19.13) (gastrointestinal adenocarcinoma)
  
• dermatomyositis (bronchus, breast, stomach, ovary)
  
• thrombophlebitis migrans (pancreatic carcinoma)
  
• flushing (carcinoid syndrome)
  
• necrolytic migratory erythema (glucagonoma)
  
• pyoderma gangrenosum (Table 19.8, Plate 19.14) (myeloma)
  
• acquired ichthyosis (lymphoma).

Miscellaneous Disorders

• liver disease – pruritus, palmar erythema, spider naevi, xanthelasma(ta)
  
• inflammatory bowel disease – erythema nodosum, pyoderma gangrenosum (Table 19.8, Plate 19.14), buccal mucosal and perianal ulceration
  
• amyloidosis – yellow waxy periorbital and perianal plaques
  
• scurvy (due to vitamin C deficiency) – perifollicular purpura, easy bruising, bleeding gums, poor wound healing
  
• pellagra (due to nicotinic acid deficiency) – triad of dermatitis (in sun-exposed areas, e.g. ‘Casal’s necklace’), diarrhoea and dementia
  
• neurofibromatosis – café-au-lait spots, axillary freckling, neurofibromas
  
• porphyria – photosensitive rash/blistering in certain types of porphyria (see p. 254)
  
• Ehlers–Danlos syndrome – skin hyperextensibility and fragility
  
• tuberous sclerosis complex (Epiloia) – hamartomas, angiofibromas, shagreen patch, periungal fibromas, hypopigmented (ash leaf) macules
  
• Peutz–Jeghers syndrome – pigmented macules (lentigines) in the mouth, on the lips, hands and feet
  
• hereditary haemorrhagic telangiectasia – facial telangiectasia
  
• pseudoexanthoma elasticum – ‘plucked chicken’ skin appearance

Bullous Disorders

Pemphigus is a relatively rare disorder of middle age, some of the characteristics of which are explained by the very superficial site of the lesions: clinically, it presents with widespread erosions and relatively few bullae (because they rupture so easily, leaving flaccid blisters), which are located over the limbs and trunk (Plate 19.15). Most patients have lesions in the mouth and these may be the only visible lesions in the early stages. The surrounding skin is normal. The superficial skin layer at the edge of a blister can be moved over the deeper layers (Nikolsky’s sign) and tends to disintegrate. Lesions appear at sites of pressure and trauma and are painful. Secondary bacterial infection may complicate the primary condition.

Investigation

• skin biopsy – for histopathology (to confirm superficial nature of the blister/bulla) and direct immunofluorescence on perilesional tissue (which shows staining around epidermal cells with antibodies directed against immunoglobulin G (IgG) and C3)
  
• serum for detection of anti-epithelial antibody

Management

Aggressive management is required including:

• High dose systemic corticosteroids (e.g. prednisolone initially 60–120 mg/day), with gradual dose tapering as blistering settles. Steroid-sparing agents (e.g. azathioprine, cyclophosphamide, methotrexate) are often susbstituted after the acute phase has subsided.
  
• Secondary bacterial infection is common and should be treated promptly.
  
• Significant fluid and protein loss may occur from weeping skin, and supportive treatment (including enteral/parenteral feeding in cases of severe oral involvement) may be required.

Pemphigoid

In contrast to pemphigus, blisters are subepidermal.

Clinical Presentation

Bullous pemphigoid affects those > 60 years of age. Clinically, it often presents with prodromal itch ± areas of erythema, which may predate the appearance of bullae by several weeks. Numerous tense, subepidermal bullae then form, ranging in size from a few millimetres to several centimetres (Plate 19.16). They are less likely to rupture than in pemphigus, but this can be provoked by trauma. Nikolsky’s sign is negative. Scarring is rare and only a small number of cases develop mucosal ulceration.

Cicatricial pemphigoid is a distinct variant in which scarring occurs and can be pronounced.

Investigation

• Skin biopsy – for histopathology (to confirm subepidermal blister/bulla). Immunofluorescence shows linear IgG and C3 at the basement membrane).
  
• Circulating IgG against antigen in the basement membrane is detectable in the serum of approximately two-thirds of patients with bullous pemphigoid.

Management

• Moderate dose systemic corticosteroids (e.g. prednisolone initially 40–60 mg/day) are required, with dose tapering as blistering settles, which usually occurs quite rapidly in bullous pemphigoid.
  
• Long-term low dose maintenance therapy is often required; azathioprine may be susbstituted after the acute phase has subsided.

Dermatitis Herpetiformis

A rare disorder associated with subepidermal blisters. It is classically seen in the context of coeliac disease.

Clinical Presentation

Dermatitis herpetiformis is characterised by itchy erythematous papules and vesicles, which are common on the elbows and other extensor surfaces. Blisters/bullae may be burst by scratching, with marked excoriation.

Investigation

• skin biopsy – for histopathology (to confirm subepidermal blister/bulla and ‘microabscesses’ at the edge of vesicles) and direct immunofluorescence (which shows granular deposits of IgA in dermal papillae)

Management

• gluten-free diet
  
• dapsone

Benign and Malignant Skin Tumours

Skin tumours are common. Most are benign, but it is important to identify malignant or potentially malignant lesions. They may arise within the epidermis or the dermis. Clinical features and treatments for the more commonly encounted/important skin tumours are shown in Table 19.9 and Plates 19.17–19.21.

Table 19.9 Skin Tumours

Miscellaneous Skin Conditions

Abnormalities of skin pigmentation are seen in a variety of settings and may be localised to small areas or more generalised. Table 19.10 lists some of the more common causes of hypo- and hyperpigmentation.

Table 19.10 Causes of Hypo- and Hyperpigmentation

Urticaria

Urticaria describes a group of disorders that are characterised by weals, which typically appear and then disappear spontaneously in a matter of hours. Mast cell degranulation leads to vasodilatation with consequent dermal oedema. Often itching is the first symptom, followed shortly afterwards by the development of pink weals over a variable-sized area, e.g. localised in response to a nettle sting or more generalised as part of an allergic reaction (e.g. food or drug allergies). When part of a more systemic anaphylactic reaction, urticaria may be accompanied by angioedema, with swelling/oedema of the subcutaneous tissues, especially around the eyes, mouth and upper airway. A chronic relapsing form, in which attacks last for weeks, months or even years, is believed to be of autoimmune origin.

If possible, triggers should be identified and avoided. Aspirin is best avoided. Most types of urticaria respond to antihistamines (both H₁ and H₂ antagonists may be helpful). Angioedema/anaphylaxis are medical emergencies (p. 115).

Lichen Planus

Lichen planus is uncommon, usually presenting in middle age with an irritating rash affecting the flexures of the wrist and forearms, lower back, mouth and genitalia. The rash consists of discrete, purple, shiny, polygonal papules with fine white lines (‘Wickham’s striae’), often occurring in scratch marks and other sites of injury (Köbner phenomenon). The papules may be widespread or confined to one or two sites. Lesions may arise on the buccal mucosa with a white, lacy network, or in the nails without other lesions on the skin. The disorder usually resolves within 6 months but can recur. The cause is unknown, but several drugs can produce an identical eruption, e.g. gold, antimalarials and antituberculous drugs. The epidermis is infiltrated with T cells.

Topical corticosteroids are usually sufficient to suppress symptoms until resolution has occurred. Systemic corticosteroids or ciclosporin may be required for extensive/severe disease.

Pityriasis Rosea

A self-limiting disorder, of unknown aetiology, commonest in children and young adults. Following a mild prodromal illness one or more ‘herald patches’ (red, oval, scaly) appear either on the trunk or arm. Several days later, multiple pink/red oval patches erupt over the trunk, upper arms and thighs, with the long axis of the oval appearing to follow individual dermatomes/spinal roots. It resolves spontaneously over 6–8 weeks.

Disorders of the Hair and Nails

Stay updated, free articles. Join our Telegram channel

Join