Presentation: pigmented skin lesion

Pigmented lesions are seen daily in general practice, and almost every patient has some. Careful examination aided by dermoscopy rules out almost all serious lesions — the task is separating the benign categories below from the small minority needing biopsy or referral.

Suspicious features

Most naevi are stable and unremarkable. Get an expert opinion if a lesion changes size, shape, structure or colour; a new naevus develops after age 40; a lesion looks different from the patient’s other naevi (the “ugly duckling” sign); it shows ABCD features (asymmetry, border irregularity, colour variation, diameter over 6mm); or it is bleeding, crusted or itchy.

Differential diagnosis

Non-melanocytic

• Pigmented basal cell carcinoma and in-situ squamous cell carcinoma (Bowen’s disease) — may be heavily pigmented enough to mask the diagnosis; dermoscopy usually reveals atypical vessels and a pigment pattern that prompts the correct call.
• Seborrhoeic keratosis — very common, usually a typical appearance, but malignancy can occasionally arise within one that looks otherwise benign.
• Solar keratoses
• Dermatofibroma — a firm nodule that dimples when pinched from the sides; stable and benign, though rare malignant transformation (dermatofibrosarcoma protuberans) is a reason to remove an enlarging one.
• Pyogenic granuloma
• Foreign body granuloma
• Talon noir (black heel)
• Tinea nigra
• Becker naevus — an epidermal naevus, usually around the shoulder; isolated but occasionally part of a congenital syndrome.
• Haemangioma — usually straightforward, but a thrombosed one can look very dark and mimic a pigmented lesion.
• Amelanotic melanoma — a red-lesion mimic: fast-growing, sometimes presents as a presumed abscess with no pus on drainage, and carries a worse prognosis than most melanomas. Any firm red raised lesion persisting four weeks should be biopsied.

Melanocytic

• Non-melanoma
  • Freckles and lentigines
  • Naevi
    • Congenital — roughly 1 in 100 babies; melanoma risk is very low even in large congenital naevi.
    • Acquired — junctional → compound → intradermal
      • Halo (Sutton)
      • Blue
      • Spitz
      • Dysplastic (atypical) — large (over 5mm), ill-defined borders, varying colour, flat and bumpy components. Not individually more prone to malignant change, but five or more dysplastic naevi, or 100 or more moles overall, correlate with significantly higher lifetime melanoma risk.
• Melanoma
  • Lentigo maligna (Hutchinson melanotic freckle)
  • Superficial spreading melanoma
  • Nodular melanoma
  • Acral lentiginous melanoma

Assessment and management

Diagnosis is enhanced by good lighting, magnification and dermoscopy; regular dermatoscope use is a core GP skill here. Subspecialised GPs using dermoscopy more often excise roughly half as many benign lesions per melanoma detected, versus generalist colleagues.

Most pigmented lesions need no removal. When melanoma is a genuine concern, excise the whole lesion with a narrow (2mm) margin — punch and shave biopsies should not be used on a suspicious pigmented lesion, since partial sampling can miss the area of malignant change. For ongoing risk reduction: monthly self-skin examination and prompt review of any new or changing lesion, with regular clinician skin checks (and mole-mapping/total body photography for those at high risk) in patients with multiple or atypical naevi or a prior skin cancer.