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.


Lichen planus:

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


  • 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.


  • Groin
  • Armpits
  • Umbilicus
  • Natal cleft


  • 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.


  • 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


  • 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.

Source link

Related Articles

Leave a Reply

Back to top button