Medicine

Psoriasis. Pathophysiology | by Aayush Pokharel | Sep, 2021

Aayush Pokharel
  • Chronic inflammation in the dermis driven by T-cells (Th1 and Th17) and cytokines (IL-12, IL-17, and IL-23) → hyperproliferation of keratinocytes → abnormally rapid growth of epidermis.
  • Plaque psoriasis is the most common manifestation, affecting 90% of psoriasis patients, and is the main focus of this page. Other variants are also described below.
  • Prevalence 1/50, with peaks of onset in late teens and late 50s.
  • 1/3 have a family history.

Flare-ups can be triggered by:

  • Alcohol and smoking.
  • Stress
  • UV light, though sunlight often symptoms.
  • Medication: lithium, antimalarials, β-blockers, ACE inhibitors, NSAIDs, steroid withdrawal.
  • .

Skin lesions:

  • Well-demarcated red plaques (raised areas) covered in white scales.
  • Itchy, though wide variability in severity.
  • No ooze

Areas affected:

  • Symmetrical
  • Limbs, especially extensor surfaces of knees and elbows.
  • Trunk
  • Palms and soles.
  • On examination, make sure to check behind ears, in scalp, and in umbilicus.

Nail signs, seen in 50%:

  • Pitting: small indentations.
  • Onycholysis: plate separation. Due to subungual hyperkeratosis.
  • Oil drop sign: yellow-red discolouration.

Other manifestations:

  • Psoriatic arthritis seen in 15%.
  • Rarely, can develop into erythrodermic or pustular psoriasis.

Eczema:

Lichen planus:

  • Purple pruritic papules with thin white lines (Wickham’s striae). May coalesce into plaques.
  • Sites: flexor surfaces, palms, soles, wrists, ankles.

Others:

  • Discoid lupus.
  • Tinea corporis.

Regular emollients plus ≥1 of steroids, vitamin A or D analogues, or coal tar. Drug choices:

  • Emollients: options include Diprobase, Epaderm, and E45. Ointments are better than creams for the dry scaly lesions of psoriasis.
  • Corticosteroids: typically used for flares. Betnovate (betamethasone valerate) for trunk and limb (4 weeks); hydrocortisone or Eumovate (clobetasone) for face, flexures, and genitals (2 weeks).
  • Vitamin D analogues — calcipotriol or tacalcitol — usually 1st line for long-term treatment.
  • Vitamin A analogues: dithranol, tazarotene.

Scalp psoriasis:

  • Mild: coal tar-based shampoo.
  • Severe flare: potent corticosteroid, then scale removal agent (salicylic acid, emollient), then vitamin D analogue.

Those with extensive disease (>10% body affected), moderate score on Physician’s Global Assessment, or nail disease, can be offered 2nd and 3rd line treatment at the same time.

  • 1st line is UVB.
  • 2nd line is PUVA: photosensitizing drug (Psoralen) followed by UVA. Effective but carries cancer risk.
  • Methotrexate is 1st line.
  • Ciclosporin for flares.
  • Acitretin, a retinoid, if the others are ineffective.
  • Biologics if still unresponsive: ixekizumab, etanercept, infliximab, adalimumab.

Aka ‘inverse psoriasis’, due to its inverted distribution relative to plaque psoriasis.

Distribution:

  • Groin
  • Armpits
  • Umbilicus
  • Natal cleft

Appearance:

  • Red, shiny and smooth.
  • Less scaly.
  • Small, drop-like papules on trunk, typically 2 weeks after streptococcal pharyngitis.
  • Commoner in young people.

Sterile pustules (neutrophils) in skin.

Usually idiopathic, or triggered by:

  • Sudden steroid withdrawal.
  • Drugs e.g. lithium.
  • Topical psoriasis treatments.
  • Infection
  • Pregnancy

Can be a life-threatening acute form, or a more subacute/chronic disease known as annular pustular psoriasis, which is commoner in children.

Palmoplantar pustulosis, which resembles a localised form of GPP, is in fact a separate condition.

Acute:

  • First sign is red, tender skin.
  • Pustules develop within hours then desquamate.
  • Most commonly affects armpits and anogenital region.
  • Less commonly affects face, tongue, and nails.
  • Systemic symptoms: fever, malaise, nausea.

Annular pustular psoriasis:

  • Annular (ring-shaped) red plaques with pustules on the periphery.
  • Affects trunk and limbs.
  • Fewer systemic symptoms.
  • Supportive care including fluids and emollients.
  • Stop causative drugs.
  • Refer to dermatology as systemic therapy often needed: acitretin, methotrexate, or ciclosporin.

>90% of skin turning red.

  • Psoriasis (erythrodermic psoriasis). Usually in a patient with known plaque psoriasis and very rarely is a first presentation. The triggers are similar to those of any psoriasis exacerbation.
  • Eczema
  • Drugs. Many causes, including carbamazepine, phenytoin, vancomycin, and penicillins.
  • Lymphoma
  • Idiopathic

Skin:

  • Red, warm, skin.
  • Pain and itch.

Systemic symptoms and complications:

  • Hypovolaemia from skin failure, sepsis, and high output HF.
  • Poikilothermia: loss of temperature control. Peripheries may be warm but core is cold. Can also be hyperthermic due to impaired sweating: watch for ‘fever’ not responding to antibiotics.
  • Oedema due to hypoalbuminaemia, reactive oedema, and high output HF.
  • Establish cause. Stop (and replace) drugs if needed.
  • Fluids
  • Emollients
  • Temperature control in poikilothermia.
  • Monitor for sepsis.
  • Treat oedema with positioning, not diuretics.

Vitamin D3 analogue which alters T cell transcription.

  • Less messy than dithranol but less effective.
  • Can be prescribed in primary care.

↑Ca2+ st

Vitamin A analogue which disrupts mitochondria → ↓cell division so ↓hyperkeratosis.

Comes as a paste.

  • Stains clothes (permanent) and skin (non-permanent).
  • Chemical burn.

Keratolytic → skin sheds.

Broken skin.

  • Irritant
  • Stain
  • Desquamation

This information is taken from Medicos PDF app. You get the app from Google Play Store for free. For more information go through the app.


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