Psoriasis

Introduction

Psoriasis is a a common chronic inflammatory skin condition, characterised by raised, red, itchy, scaly plaques on the skin. With treatment, it often follows a relapsing and remitting course, although in more severe cases it may never fully remit.

There is a strong genetic component to the inheritance of the disorder, and there are thought to be environmental triggers that bring on the condition in a genetically susceptible individual.

Pathologically, it is caused by a T-cell mediated abnormal immune response. The T cells release cytokines, resulting in keratinocyte proliferation.

Dermatologists may classify psoriasis into various subtypes, such as guttate psoriasis or palmar-pustular. 

In about 10-15% cases it is associated with psoriatic arthritis.

Epidemiology

• Affects 2-4% of the population
• Can start at any age, but has two peaks of incidence:
  • 15-25 years
  • 50-60 years
• 1/3 of patients have a relative with the condition
• More common in caucasians
• Usually life-long

Aetiology

Risk factors include:

• Genetic susceptibility
• Smoking
• Obesity
• Psychological stressors

Pathology

• Parakeratosis: retained nuclei
• Acanthosis: thick epidermis
• Absent granular layer
• Lengthened rete ridges
• Thin dermal papillae
• Dilated, tortuous capillaries
• Munro’s micro-abscesses
• T-cells in upper dermis

Clinical features

• Symmetrical
• Red scaly plaques
  • Scale is usually white or silvery coloured
• Often extensor surfaces – e.g. front of knees, backs of elbows
  • As opposed to eczema which is commonly the flexor surfaces
• Common locations:
  • Scalp (particularly behind ears)
    • Sometimes only the scalp is affected
  • Elbows
  • Knees
  • Can affect any part of the body
• Itchy (!)
  • Often accompanied by excoriation, or in longer term more severe cases – lichenification (thick leathery skin)
• Resolving patches of psoriasis often leave brown coloured marks that generally fade over a period of months

• Classical [or typical or chronic plaque psoriasis]
  • The most common type of psoriasis – approx 90% of cases
  • Plaques: Well-circumscribed erythematous plaques with silver scaling
    • Usually plaques >3cm diameter
  • Distribution: Esp. on extensor surfaces [elbow, knee], scalp/hairline, sacral
  • Features: Pain, itch [but less than eczema/dermatitis]
  • Nail changes – e.g. pits or ridges on nails
  • Auspitzs sign: Bleeding on scale removal
• Guttate psoriasis
  • Age: Young
  • Onset: often follows streptococcal tonsillitis (acute guttate psoriasis)
  • Plaques: Multiple discoid erythematous and scaly macules and plaques on trunk
    • Tend to be smaller than the plaques of typical psoriasis and not in the typical locations (trunk rather than flexor surfaces)
    • Plaques usually <3cm diameter
  • Good prognosis – cases of acute guttate psoriasis often resolve spontaneously after several months
  • In some instances it can become chronic, and chronic guttate psoriasis can often be much more resistant to treatment than classical psoriasis

• Palmoplanar pustular
  • Plaques: Yellow-brown pustules on palms and soles
• Flexoral
  • Plaques: Erythematous, but not scaly
  • Distribution: Submammary, axillary, anogenital, umbilical
  • Epidemiology: Esp. women; also the elderly and HIV +ve
  • Can be difficult to tell apart from eczema or difficult to tell that it is psoriasis due to its unusual distribution
• Erythrodermic [emergency!]
  • Features: Acute onset of erythroderma and pustular plaques
  • Management: Methotrexate
  • Others: only scales; only nails; and napkin

Nails

• Features: Pitting, onycholysis [nail lifting off the bed]; subungal hyperkeratosis; Beaus lines [horizontal, across the nail]
• Differential diagnosis: fungal infection, alopecia areata

Psoriatic arthropathy

• Patterns: [1] AnkSpond-like/spondylitis; [2] RA-like/symmetrical; [3] Asymmetrical, <3 joints;[4] DIP joints, hands; [5] Arthritis multilans

Differential diagnosis

• Dermatitis/eczema: discoid or seborrhoeic
• Lichen planus
• Pityriasis rosea [esp. guttate psoriasis]
• 2^o stage of syphilis
• Reiter’s syndrome [Esp. palmoplanar psoriasis]
• Discoid lupus
• Syphilis

Precipitating factors

• Trauma [known as Koebner’s phenomena]
• Infection
• Drugs: β-blockers, lithium, anti-malarials; NSAIDs and ACE-Is
• Emotional stress
• Sunlight
• Puberty
• Menopause
• Alcohol
• Obesity (insulin resistance)
• Smoking

Associated Disorders

• Psoriatic arthritis
  • Affects about 13% of psoriasis patients
  • Tends to have onset within the first 10 years of onset dermatological psoriasis
  • Also an associated with spondyloarthritis (e.g. ankylosing spondylitis)
• Inflammatory bowel disease
• Uveitis
• Coeliac disease
• Metabolic syndrome
  • T2DM
  • Hypertension
  • Hyperlipidaemia
  • Gout
  • Cardiovascular disease

Management

• Explain the diagnosis and advise about reducing the severity through management of lifestyle factors
• Smoking cessation
• Reduction of alcohol intake
• Weight loss
• Avoidance of sun exposure
• Management of stress / mental health

• Emollients
• Corticosteroids
  • The mainstay of treatment
  • In the past associated with “rebound psoriasis” on cessation of treatment – but this is thought to be rare. Higher risk when used alone and not in combination with vitamin D analogies – and as such are almost always prescribed with vitamin D analogues
  • Start with potent agent – e.g. betamethasone 0.1% (betnovate)
  • Dosing regimen recommends morning application of steroid and evening application of vitamin D analogue
  • Sometimes comes as a combined agent with a vitamin D analogue – such as daivobet or Enstillar Foam (betamethasone + Vit D) – which can greatly improve compliance!
  • If not responsding to steroids, or steroids + Vit D used separately, consider swapping to daivobet +/- adding coal tar preparations
  • Be aware of side effects of long term use of topical steroid agents – include stretch marks (striae) and skin atrophy / thinning of the skin
  • For the face, advise steroid only, not a combination – e.g. hydrocortisone 1%
• Vit. D analogues
  • Calcipotriol, tacalcitol and calcitriol
  • Mechanism: ↓ cell proliferation
  • Side-effects: Skin irritation, hypercalaemia if overuse
• Coal tar preparations
  • Mechanism: Inhibit DNA synthesis
  • Problems: Smelly, messy
  • Less concentrate version are less messy and just as effective (1-5% coal tar)
  • Scalp psoriasis is particualyl difficult to treat and is the most commonly used location for coal tar
• Dithranol
  • Anthralin
  • Mechanism: ↓ cell proliferation
  • Side-effects: Irritates neighbouring normal skin, stains clothes purple
• Keratolytics
  • Salicylic acid
• Retinoids
  • Tazarotene

Systemic

Usually only initiated in a secondary care setting

• Phototherapy
  • UVB for classic/plaque and especially for guttate psoriasis
    • Narrow band UVB therapy has a low risk of burning and ow risk of long-term sun damage. It is used before UVA
  • PUVA
    • Used in cases not responsive to UVA
    • Stands for “photochemotherapy UVA”
    • More likely to cause long-term skin damage and increases risk of skin cancer
    • Often used in combination with retinoids to reduce the dose of PUVA
• Retinoids
  • Acitretin
  • Note: Therapeutic effect after 4-6 weeks; used for <6 months
  • Side-effects
    • Teratogenic for up to 3 years
    • Dry mucous membranes: skin, eyes, lips [may cause epistaxis]
    • Others: hepatotoxicity; deranged lipid profile
•  Immunosuppressants
  • Methotrexate
  • Also ciclosporin, azathioprine, and hydroxyurea
  • Often used when all the above have failed
  • usually used in short-courses of 4-12 weeks and repeated in case of relapse
• Biological agents
  • Used when treatment to all else has failed or is contraindicated
  • Examples: etanercept, adalimumab, infliximab

Complicated regains of various topical agents lead to poor compliance and often then poor response to treatment.

Typical Regimen

Treating classic/typical psoriasis

• 1^st line: Vit. D analogues +/- topical steroids + tar or salicylic acid ± UVB
• 2^nd line: Retinoids, PUVA, UVB, immunosuppressants
• 3^rd line: Dithranol
• Goekerman regime = Tar + UVB
• Ingram regime = Goekerman + dithranol

Indications for referral

The majority of cases of psoriasis is managed in primary care. Possible indications for referral to dermatology include:

• >10% body surface area affected
• Psoriasis not responding to topical treatment
• Psoriasis in children
• Psoriasis having a major impact on psychological health

Complications

• Mental health disorders – e.g. depression or anxiety, secondary to their skin condition
• There is an associated with psoriasis and reduced rates of employment

Prognosis

• Course is very variable
• Often relapses
• Poor prognostic factors include strong family history and early age of onset
• Over-use of steroids can cause pustular flares – which can cause serious systemic infection

Flashcard

References

• Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
• Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
• Psoriasis – Dermnet NZ
• Psoriasis – Patient.info

Read more about our sources

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