Differential diagnoses: Psoriasis

Dr Nigel Stollery compares four types of psoriasis and offers clues for their diagnosis.

Plaque psoriasis


  • Chronic condition affecting about 2% of the population
  • Any areas can be affected, but occurs most commonly on extensor surfaces
  • Well-demarcated plaques with thick scale
  • Scales have a silvery surface and bleed if picked
  • Can develop at any age


  • Treatment includes emollients, topical vitamin D derivatives or vitamin D/steroids combinations
  • UV light usually beneficial
  • Severe cases require referral to secondary care
  • Phototherapy can be helpful
  • In severe cases, biological agents can be beneficial

Guttate psoriasis


  • Typically 1-10mm diameter drop-like salmon-coloured papules with surface scale
  • Monomorphic appearance
  • Starts on torso before spreading to limbs
  • Acute onset usually follows URTI from group B haemolytic streptococcus
  • Most common in under-30s
  • May be seen in association with beta blockers and lithium
  • Biopsy can aid diagnosis


  • Usually self limiting
  • Resolves over weeks to months
  • Emollients can be helpful
  • May progress to plaque psoriasis
  • In severe cases, phototherapy can be beneficial

Palmoplantar psoriasis


  • Thought to be a disorder of eccrine sweat glands
  • Affects palms and soles
  • 10-20% have psoriasis elsewhere
  • Rarely occurs in children. More common in women than men
  • More common in smokers
  • Differential diagnoses include fungal infections


  • No known cure
  • If a smoker, advise on cessation
  • Regular application of emollients will help
  • Other treatments include topical steroids, acitretin and psoralen plus UVA light therapy
  • In severe cases, biological agents can be beneficial

Flexural psoriasis


  • Common condition affecting armpits, groin, submammary folds and umbilicus
  • Scale usually absent
  • Skin looks red, shiny and smooth
  • Borders usually well demarcated
  • Psoriasis may also be present in non-flexural areas
  • Secondary infections common


  • Treatment includes emollients and topical steroids
  • Vitamin D analogues helpful but may be poorly tolerated because of irritation
  • Topical calcineurin inhibitors are an alternative to steroids
  • Phototherapy is relatively ineffective in most cases

Dr Stollery is a GP in Kibworth, Leicestershire, and clinical assistant in dermatology at Leicester Royal Infirmary

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