Differential diagnoses - Pigmented skin lesions

Dr Nigel Stollery compares four presentations and offers clues for their diagnosis.

Compound naevus


  • Common benign pigmented naevus arising in melanocytes
  • Colour varies from white to dark brown
  • May occur congenitally
  • Usually raised above the surface of the skin
  • Size varies from 2-7mm in diameter


  • Treatment not always needed
  • Indications for removal include diagnostic uncertainty, cosmetic reasons, or if there is repeated trauma
  • Treatment of choice is surgical excision
  • Whole lesions should be removed and sent for histology

Malignant melanoma


  • Malignant skin lesion with potential to be life-threatening
  • Metastatic spread will occur if untreated
  • Incidence increasing
  • Occurs at younger age than other skin malignancies
  • More common in skin types 1 and 2 and with UV exposure
  • 30% develop in existing naevi


  • Early excision is treatment of choice
  • Whole lesions should be removed and sent for histology with 2mm margin
  • Once diagnosis is confirmed, wide excision required
  • When spread has occurred, prognosis is poor, with few treatment options

Pigmented basal cell carcinoma


  • Most common type of skin malignancy
  • Incidence increases with age
  • Occur mainly on sun-exposed areas of skin
  • When pigmented, differential includes malignant melanoma
  • Lesions have little potential for metastatic spread


  • Excision is the treatment of choice
  • Histology to check for complete excision and confirm diagnosis
  • Further lesions commonly occur
  • Advise patients on sun protection

Seborrhoeic keratosis


  • Very common benign lesions
  • Pale to dark brown in colour
  • Stuck-on appearance, with crusted warty surface
  • Incidence increases with age
  • No potential for malignant transformation
  • Typical keratin plugs and horny cysts when viewed with a lens


  • Treatment not usually necessary
  • If required, cryotherapy can be undertaken
  • Other treatments include curettage and cautery

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

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