Dermatoscopy of flat pigmented facial lesions: diagnostic challenge between pigmented actinic keratosis and lentigo maligna.

BACKGROUND

The similarity between clinical pictures of pigmented actinic keratosis (PAK) and lentigo maligna (LM) is well known.

OBJECTIVES

To investigate the frequency of dermatoscopic findings suggestive of LM/lentigo maligna melanoma (LMM) in the other facial pigmented skin lesions (FPSL) and to assess the distinguishing dermoscopic criteria of PAK and LM.

METHODS

Eighty-nine FPSL were evaluated with conventional dermatoscopy. The lesions showing one or more dermatoscopic features considered as specific patterns for the diagnosis of LM/LMM, mainly slate-grey to black dots and globules, slate-grey areas, annular-granular pattern, asymmetrical pigmented follicular openings, black blotches, rhomboidal structures, hyperpigmented rim of follicular openings, slate-grey streaks and dark streaks, were included in the study selectively.

RESULTS

PAK was diagnosed in 67, LM or LMM in 20 and lichen planus-like keratosis in two lesions, histopathologically. Eleven essential dermatoscopic features were observed in facial PAK: slate-grey dots (70%); annular-granular pattern (39%); rhomboidal structures (36%); pseudonetwork (36%); black globules (34%); slate-grey globules (33%); black dots (30%); asymmetrical pigmented follicular openings (25%); hyperpigmented rim of follicular openings (21%); slate-grey areas (18%); and streaks (3%).

CONCLUSIONS

PAK has a striking similarity to LM/LMM in clinical and dermatoscopic features, thus representing a diagnostic challange. All dermatoscopic findings except black blotches were observed in PAK. As dermatoscopic diagnosis of a pigmented skin lesion cannot be based on the presence of a single criterion, we may conclude that histopathology still remains the gold standard for correct diagnosis.