Psoriasis Flashcards
Clinical summary of psoriasis
-Rash characterised by scaly red plaques, with a predilection for the extensor surfaces, the nails and scalp
-Runs a waxing and waning course and is associated in around 5-30% of patients with an inflammatory polyarthropathy, and an increased risk of the metabolic syndrome and cardiovascular disease.
-Itch is common but not as severe as in disorders such as eczema or scabies.
-Highly hereditable, cannot be cured, but can be managed with simple emollients through to potent immunosuppressives and ‘biologics’
Histological features of psoriasis
-Epidermal hyperproliferation (‘keratinocyte problem’)
-A pronounced inflammatory infiltrate (‘immune system problem’)
Pathogenesis of psoriasis
-Epidermal differentiation deranged (time taken shortened= cannot mature properly so rushed in immature state) with hyperproliferation (with lots of mitoses evident)
-Relative absence of the granular layer with retention of nuclei within the stratum corneum (parakeratosis)
-Acanthosis (thickening of the viable cell layers), with elongation of the rete ridges
-Inflammation: oedema in the dermis, a pronounced T-cell rich inflammatory infiltrate in dermis, together with polymorphs in the dermis and in the epidermis.
=In the epidermis polymorphs may form little micro-abscesses (Munro micro-abscesses).
=Collections of polymorphs visible to the naked eye (i.e sterile pustules= pustular psoriasis)
=Capillaries (in the dermis) are increased in number and length
What causes psoriasis?
-Hereditable
=If both parents have psoriasis, the risk for each child developing psoriasis is 40-50%.
=If one parent is affected, the risk is ~15%
-Candidate genes involved in:
=Innate immunity
=Adaptive immunity
=The interface between the innate and the adaptive immune system
=Genes involved in skin barrier function and keratinocyte signalling pathways
=Various cytokines (e.g.Il-23) seem causally involved (i.e. if they are blocked, the disease improves)
-Key players involved in the pathogenesis of psoriasis include:
=Antigen presenting cells, T cells,, HLA (particularly HLA-Cw6)
=Tumour necrosis factor (TNF), NF-𝞳B, interferons
-Although psoriasis has been labelled an autoimmune disorder no autoantigen has been identified.
Epidemiology of psoriasis
~2% of the European population, ~5% North America.
-Lower in Africans, Norwegian Lapps and some Asians, with rates in the order of 0.5%
-Psoriatic arthritis has been reported to affect between 5% and 30% of patients with psoriasis
-Type 1: starts in the later teenage years/early adulthood and there is more likely to be a family history and positivity for certain HLA groups (HLA-Cw6)
-Type 2: Onset in the 5th or 6th decades
Triggering factors of psoriasis
-Streptococcal sore throat (T-cell role?)
=Other infections may also precipitate exacerbations of psoriasis: HIV aggravates psoriasis, and undiagnosed HIV may present with worsening of a known case of psoriasis
-Certain drugs, such as lithium, betablockers, interferon-α and chloroquine
-Bone marrow transplant
-Obesity, smoking and alcohol
-Heavy alcohol consumption= worsening of the disease, and smoking is in particular associated with some types of pustular psoriasis.
-Koebner phenomenon (psoriatic plaque at site of skin insult with 2 week lag)
=sunburn, surgery, viral exanthema, and acupuncture needles
-Psychogenic factors: stress
Types of psoriasis
-Stable plaque psoriasis
-Guttate psoriasis
-Erythrodermic psoriasis
-Pustular psoriasis
-Flexural, or inverse, psoriasis
-Palmoplantar psoriasis
-Nail psoriasis
Describe Stable Chronic Plaque Psoriasis
-Psoriatic plaque: scaly red well demarcated plaque, most commonly seen on the extensor surfaces, such as the elbows or knees= stable chronic plaque psoriasis (if stable over years)
-Erythema can be obscured by an excess of silvery scale
=fraction of a millimetre through to barnacle like lesions that could rarely be up to 1cm thick.
=If the scales removed with keratolytic agents, such as salicylic acid, or the scale rendered less visible with emollients, then the underlying erythema is exposed and is more obvious.
=In darker skin tones, erythema may be less obvious but the clues to the diagnosis lie in the distribution and scale of the plaques
Describe guttate psoriasis
-Characterised by up to several hundred small lesions, a centimetre or less, and follows a streptococcal sore throat by 2-3 weeks (multiple teardrop lesions)
-Rash most common on the trunk, and less often as extensive on the face or the limbs.
-Often the first episode of psoriasis an individual develops, and is most commonly seen in children and young adults.
-Prophylactic penicillin to avoid sore throat= no rash BUT few people are treated with tonsillectomy or with continuous antibiotics
Describe erythrodermic psoriasis
-Any rash that affects 90% or more of the body surface
-Although it is possible to see patients with plaque psoriasis that is this extensive, you may also see patients who just appear to have widespread erythema with or without apparent oedema of their skin, and without much scale.
-Patients with the former are fairly easy to diagnose, whereas if the patient just has erythema, then the differential is that of any cause of erythroderma (if this is the presenting episode of psoriasis, making a firm diagnosis may be impossible, until later).
Describe pustular psoriasis
-Microscopic collections of polymorphs (Munromicro-abscesses) in the epidermis.
=If large: visible to the naked eye.
-2 forms: Palmoplantar pustular psoriasis (PPP) and Generalised pustular psoriasis (Von Zumbusch)
-PPP: pustules are found on the palms and soles (and not elsewhere)- could be distinct disorder
-Generalised: widespread or erythrodermic psoriasis and develop thousands of small white sterile pustules across the body.
=can become systemically very ill, with a pyrexia, rigours and severe malaise.
-Plaques of psoriasis that are continually treated with steroids may become pustular.
-Sudden withdrawal of steroids: pustules may develop
Describe flexural/ inverse psoriasis
-Psoriasis seems to predominate in the flexures (natal cleft, inframammary, antecubital fossae, axillae etc).
-The rash will be red and shiny, but scale will generally be lacking= smooth
Describe palmoplantar psoriasis
Some patients with psoriasis have chronic hyperkeratotic psoriasis without pustules that is often indistinguishable from chronic hand eczema
Describe nail psoriasis
-Nail changes= very common in psoriasis
=Pitting of the nail plate (reflecting the site of foci of parakeratosis) in the dorsal nail matrix. An occasional pit is not uncommon in normal people, but patients with psoriasis often have scores of them
=Onycholysis — separation of the distal nail from the nail bed
=Oily spots — a hazy, slightly yellowy/brown appearance of part of the nail.
-Psoriasis can destroy the normal anatomy of the nails
Describe scalp psoriasis
-Scalp very commonly affected
-Discrete lesions, and spread beyond the hair line onto the borders of the scalp
-Scales usually adhere to the hair shafts
-Very rarely alopecia may develop under the plaques.
=Topical treatments are hard to apply.
=Scalp psoriasis is rare in those who have lost their hair.
=Itch can be a major problem in psoriasis of the scalp.
