Contiguous lesions in lentigo maligna

Background: Determining the best biopsy technique for a suspected lentigo maligna can be challenging. Because complete excisional biopsy is rarely practical, the physician is left to choose an appropriate area to biopsy. Sampling error can have devastating consequences, especially if the biopsy demonstrates a pigmented lesion that was considered in the clinical differential diagnosis. The presence of a solar lentigo, pigmented actinic keratosis, or reticulated seborrheic keratosis could mislead the pathologist and clinician to the erroneous conclusion that the incisional specimen is representative of the whole, and that no lentigo maligna is present. Objective: We have often observed the presence of a contiguous pigmented lesion adjacent to lentigo maligna. The current study was designed to determine how frequently this phenomenon occurs. Methods: We studied Mohs debulking specimens of lentigo maligna, and broad shave biopsy specimens of pigmented lesions on heavily sun-damaged areas of the skin proven to be lentigo maligna. Results: Contiguous pigmented lesions were present in 48% of the specimens. The most common lesion was a benign solar lentigo (30%), followed by pigmented actinic keratosis (24%). Conclusion: Recognition of this phenomenon may prevent misdiagnosis of lentigo maligna related to sampling error.