Lentigo maligna (LM), also known as Hutchinson freckle, is a type of melanoma in situ that is typically seen on sun-exposed skin. It has indistinct margins with predominantly brown and black coloration. LM is usually seen on older, mostly fair-skinned patients who have a history of extensive sun exposure. Its preferred sites include the face, ears, neck, and upper extremities.
LM is, by definition, entirely superficial and therefore safe. Its main significance is that it can become focally invasive to the dermis, a phenomenon termed lentigo maligna melanoma (LMM). When that occurs, the clusters of spindle-shaped atypical cells can then progress to a vertical growth phase, resulting in intravascular invasion that eventuates in metastasis.
LMs grow so slowly that they often escape detection; they are sometimes mistaken for solar lentigines (SL). They can “collide” with SLs or other benign lesions (eg, seborrheic keratoses), which can effectively camouflage them. Suspicion is usually triggered by change (color, size) in a lesion.
Biopsy is the only method of detection. In this case, the central portion of this large, oddly pigmented and bordered, multicolored patch was excised and the darkest, most irregular part of the lesion collected. This is the gold standard for biopsy of a potential melanoma. A large deep shave biopsy (“saucerization”) would have accomplished the same thing; studies show that neither process will cause metastasis. The main mistake to avoid is performing a single punch biopsy, which risks a false-negative result.
The definitive surgical approach is to remove the lesion with a 1-cm margin around it and into the underlying adipose layer. The wound can either be left to heal by secondary intention or closed primarily. Either way, this patient’s prognosis is excellent, unless the final pathology report indicates focal invasion. With a patient of this age, the LM could have been left alone—although, once discovered, LM is irresistibly compelling to treat.
TAKE-HOME LEARNING POINTS
• Lentigo maligna (LM) is a type of melanoma in situ with the potential to progress to lentigo maligna melanoma, an invasive form of early melanoma.
• LM is common on sun-exposed skin of older patients with a history of excessive sun exposure.
• Faces, ears, arms, and necks are common areas for LM to manifest.
• Biopsy of suspected melanoma should incorporate a significant portion of the darkest, most irregular part of the lesion; it can be done by incisional technique or deep saucerization.
• LM is also known as Hutchinson freckle, since it often resembles a large, irregularly bordered and pigmented freckle.