A 70-year-old man presents with a 1-month history of an enlarging, irregularly pigmented macule on his forehead. He has worked on a farm for the past 50 years. He denies any significant medical history. On physical examination, the lesion is found to be non-scaly and smooth. No other problems are noted.
Submit your diagnosis to see full explanation.
Lentigo maligna is considered to be a form of melanoma in situ. It increases in size progressively over a period of years and has a significant chance of transitioning into invasive lentigo maligna melanoma.
The peak incidence of lentigo maligna is between age 65 and 80 years, with a recent rise in incidence in younger populations.1 Fair-skinned people who have a history of nonmelanoma skin cancer and coexisting signs of actinic skin damage are at higher risk for lentigo maligna and lentigo maligna melanoma.1
Lentigo maligna can be difficult to diagnose because it can mimic numerous other lesions, including early-stage seborrheic keratosis, pigmented actinic keratosis, benign melanocytic nevus, lichen planus-like keratosis, and solar lentigo.1,2 Excisional biopsy with histopathology is the gold standard for definitive diagnosis of lentigo maligna. Histology shows proliferating small nests or single cells of spindle-shaped, atypical melanocytes at the dermal-epidermal junction. There is normally additional evidence of chronic solar damage, such as elastosis, atrophy of the epidermis, effacement of rete ridges, and inflammatory dermal infiltrate.
Dermatoscope evaluation is also useful to help confirm clinical suspicion. There are 4 key defining characteristics of lentigo maligna: asymmetric pigmented follicular openings, dark rhomboidal structures, annular-granular structures, and perifollicular slate-gray dots and globules. It is important to note that these findings are not pathognomonic for lentigo maligna because other diseases may have similar overlap.2
Early treatment of lentigo maligna is important because of the risk for conversion to invasive lentigo maligna melanoma. The risk for disease progression is estimated to be between 5% and 50% when left untreated.3 When adequate resources are available, Mohs surgery is the preferred method of treatment. Mohs surgery allows in-clinic evaluation of the margins of the excised lesion by a dermatopathologist to determine whether the tumor has been completely removed. Use of this technique substantially reduces recurrence (4%-5%) compared with standard surgical excision.3 Mohs surgery for lentigo maligna is performed only if the surgeon has access to Mel-5 immunostaining. If Mohs surgery is not available, other surgical methods, including geometric staged excision and spaghetti technique, have been successful in tumor eradication, with minimal recurrence.4
For patients with contraindications to surgical intervention, a combination of radiation therapy and 5% imiquimod cream application to the lesion site is also effective.4
If lentigo maligna does not progress to invasive lentigo maligna melanoma, there is no effect on life expectancy. However, because patients who have lentigo maligna typically have had high exposure to sun, evaluation for comorbid melanoma and nonmelanoma skin cancer should be performed, especially in older populations.3,4
Maura Holcomb, MD, is a resident at Baylor College of Medicine in Houston, Texas.
1. Kallini JR, Jain SK, Khachemoune A. Lentigo maligna: review of salient characteristics and management.Am J Clin Dermatol. 2013;14(6):473-480.
2. Tanaka M, Sawada M, Kobayashi K. Key points in dermoscopic differentiation between lentigo maligna and solar lentigo. J Dermatol. 2011;38(1):53-58.
3. Stevenson O, Ahmed I. Lentigo maligna: prognosis and treatment options. Am J Clin Dermatol. 2005;6(3):151-164.
4. Farshad A, Burg G, Panizzon R, Dummer R. A retrospective study of 150 patients with lentigo maligna and lentigo maligna melanoma and the efficacy of radiotherapy using Grenz or soft x-rays. Br J Dermatol. 2002;146(6):1042-1046.