Histologic similarities between lentigo maligna and dysplastic nevus: importance of clinicopathologic distinction.

BACKGROUND: Lentigo maligna (LM) can histologically simulate dysplastic nevus (DN). Partial biopsy of LM may lead to misdiagnosis.

METHODS: One hundred and fourteen cases of LM and LM melanoma (LMM) were diagnosed at the Veterans Affairs Palo Alto Health Care System (1993-2002). Biopsy and excision specimens for 68 in situ and 28 invasive melanomas were classified as having predominant classical LM features, predominant DN-like morphology, or a mixed pattern.

RESULTS: Biopsy specimens demonstrated a predominant classical pattern in 38% (25/65) LM and 36% (10/28) LMM, predominant DN-like features in 43% (28/65) LM and 25% (7/28) LMM, and mixed pattern in 15% (10/65) LM and 29% (8/28) LMM. Most LM and LMM biopsies were partial. Significant DN-like features were present in 51% LM and 57% LMM excision specimens. Median age was 72 years for LM and 73 years for LMM, mean lesion diameters were 1.3 and 1.7 cm for LM and LMM, respectively, and 85% of LM and 75% of LMM cases were located on heavily sun-exposed sites.

CONCLUSIONS: Misdiagnosis of LM or LMM as DN could have devastating results. Large pigmented lesions on sun-damaged skin in elderly individuals should warrant consideration of LM/LMM diagnosis, even in the setting of DN-like features histologically. Excisional biopsy may help to avoid misdiagnosis.