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Tuesday, 11 March 2008

Lentigo maligna simulating an actinic lentigo

A 72-year-old woman consulted for a pigmented lesion on her right forearm.

Dermoscopy revealed an asymmetric pigmented lesion with different shades of brown colour, fingerprint-like structures and moth-eaten borders. These dermoscopic signs are observed in actinic lentigos or flat seborrheic keratoses.
However, a biopsy revealed a lentigo maligna.
The lesion was excised and pathology confirmed the diagnosis of lentigo maligna melanoma in situ.

Facial lentigo maligna melanoma (LMM) typically features asymmetric follicular openings, annular-granular pattern, rhomboïdal structures and homogenous areas.

In our case of extra-facial LMM, the presentation was different and was masquerading as an actinic lentigo.

Extra-facial LMMs comprise 17,5% of LMMs. Extra-facial LMMs of men are predominantly localized on the trunk while the most frequent localization in women are on limbs. Extra-facial LMMs are thinner than facial LMMs at presentation and affect younger group of patients.

See the literature: Cox, Aitchison & Mackie. Extrafacial lentigo maligna melanoma: analysis of 71 cases and comparison with lentigo maligna melanoma of the head and neck. Brit Journal Dermatol 1998; 139: 439-43