Differential diagnoses: Crusted skin lesions

Dr Nigel Stollery compares four similar dermatology presentations.

Primary cutaneous B-cell lymphoma


  • Rare condition, which develops slowly over months or years
  • Most common on the head, neck and trunk
  • Nodular, with a red or pink appearance
  • Single or multiple tumours may be present
  • May transform into more aggressive forms


  • Diagnosis can be difficult and biopsy is usually required
  • Condition is always managed in secondary care
  • Treatment will depend on the patient's symptoms and general health, and the stage of their disease
  • Options include radiotherapy or excision

Nodular prurigo


  • Can occur anywhere that is easily scratched
  • History of recurrent trauma sometimes disclosed by patient on questioning
  • Single or multiple firm lesions
  • Condition may be associated with mental illness


  • Treatment can be difficult
  • Topical steroids may help to decrease the pruritus
  • Occlusion can be helpful

Actinic keratosis


  • Common condition
  • Rarely seen in patients with Fitzpatrick skin types IV and V
  • Incidence increases with age
  • Occurs on sun-exposed areas
  • More common in people who work outdoors and those living in hot countries
  • Lesions have a low risk of malignant transformation


  • Various treatment options are available, including topical preparations, cryotherapy, and curettage and cautery
  • Future sun protection is an important part of management in these patients
  • Usually managed in primary care
  • If diagnosis is in doubt, a biopsy can be helpful



  • More common in areas of sun-damaged skin
  • May be triggered by trauma
  • Starts as a pimple or boil, but is solid when squeezed
  • Lesion arises from hair follicle skin cells
  • Central keratin plug present
  • Rapid growth up to 2cm diameter


  • As it is difficult to differentiate from squamous cell carcinoma, suspected keratoacanthoma should be referred under the two-week wait system
  • May resolve without treatment
  • Treatment options include cryotherapy, radiotherapy or electrocautery

Dr Stollery is a GPSI in dermatology in Kibworth, Leicestershire

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