Psoriasis: pathophysiology including gene associations
- multifactorial and not yet fully understood
- genetic: associated HLA-B13, -B17, and -Cw6. Strong concordance (70%) in identical twins
- immunological: abnormal T cell activity stimulates keratinocyte proliferation. There is increasing evidence this may be mediated by a novel group of T helper cells producing IL-17, designated Th17. These cells seem to be a third T-effector cell subset in addition to Th1 and Th2
- environmental: it is recognised that psoriasis may be worsened (e.g. Skin trauma, stress), triggered (e.g. Streptococcal infection) or improved (e.g. Sunlight) by environmental factors
recognised subtypes of psoriasis and how they present
- plaque psoriasis: the most common sub-type resulting in the typical well-demarcated red, scaly patches affecting the extensor surfaces, sacrum and scalp
- flexural psoriasis: in contrast to plaque psoriasis the skin is smooth
- guttate psoriasis: transient psoriatic rash frequently triggered by a streptococcal infection. Multiple red, teardrop lesions appear on the body
- pustular psoriasis: commonly occurs on the palms and soles
other features of psoriasis
nail signs:
pitting
onycholysis (separation of the nail from the nail bed)
subungual hyperkeratosis
loss of the nail
arthritis
complications of psoriasis
- psoriatic arthropathy (around 10%)
- increased incidence of metabolic syndrome
- increased incidence of cardiovascular disease
- increased incidence of venous thromboembolism
- psychological distress
Psoriasis exacerbating fators
- trauma
- alcohol
- drugs: beta blockers, lithium, antimalarials (chloroquine and hydroxychloroquine), NSAIDs and ACE inhibitors, infliximab
- withdrawal of systemic steroids
- Streptococcal infection may trigger guttate psoriasis.
Chronic plaque psoriasis features
Chronic plaque psoriasis is the most common form of psoriasis seen in clinical practice, accounting for around 80% of presentations.
Features
* erythematous plaques covered with a silvery-white scale
* typically on the extensor surfaces such as the elbows and knees. Also common on the scalp, trunk, buttocks and periumbilical area
* clear delineation between normal and affected skin
* plaques typically range from 1 to 10 cm in size
* if the scale is removed, a red membrane with pinpoint bleeding points may be seen (Auspitz’s sign)
Guttate psoriasis presentation and features
Guttate psoriasis is more common in children and adolescents. It may be precipitated by a streptococcal infection 2-4 weeks prior to the lesions appearing.
Features
* tear drop papules on the trunk and limbs
* gutta is Latin for drop
* pink, scaly patches or plques of psoriasis
* tends to be acute onset over days
management of guttate psoriasis
Management
* most cases resolve spontaneously within 2-3 months
* there is no firm evidence to support the use of antibiotics to eradicate streptococcal infection
* topical agents as per psoriasis
* UVB phototherapy
* tonsillectomy may be necessary with recurrent episodes
Differentiating guttate psoriasis and pityriasis rosea
chronic plaque psoriasis management
- Calcipotriol + betamethasone (Dobovet)
- Tar
- Dithranol
- Tacalcitol once daily before bed and only for 12 week courses
secondary management of chronic plaque psoriasis
Phototherapy
* narrowband ultraviolet B light is now the treatment of choice. If possible this should be given 3 times a week
* photochemotherapy is also used - psoralen + ultraviolet A light (PUVA)
* adverse effects: skin ageing, squamous cell cancer (not melanoma)
Systemic therapy
* oral methotrexate is used first-line. It is particularly useful if there is associated joint disease
* ciclosporin
* systemic retinoids
* biological agents: infliximab, etanercept and adalimumab
* ustekinumab (IL-12 and IL-23 blocker) is showing promise in early trials
scalp psoriasis management
- NICE recommend the use of potent topical corticosteroids used once daily for 4 weeks
- if no improvement after 4 weeks then either use a different formulation of the potent corticosteroid (for example, a shampoo or mousse) and/or a topical agents to remove adherent scale (for example, agents containing salicylic acid, emollients and oils) before application of the potent corticosteroid
Face, flexural and genital psoriasis management
NICE recommend offering a mild or moderate potency corticosteroid applied once or twice daily for a maximum of 2 weeks
Topical corticosteroids side effects and maximum time they should be used in psoriasis depending on strength
Vitamin D analogues examples, mode of action and how they should be used
Dithranol MOA, how to use and SE
inhibits DNA synthesis
wash off after 30 mins
adverse effects include burning, staining
