Dermoscopic Features of Acral Lentiginous Melanoma in Situ

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Dermoscopic Features of Acral Lentiginous Melanoma in Situ

Did you know that acral lentiginous melanoma (ALM)—the most common type of cutaneous melanoma in Asians—often begins as a faint, discolored patch on the hands or feet? Early detection is life-saving, but spotting ALM in its earliest, non-invasive stage (called “in situ”) can be challenging. A 2019 study by dermatologists at Shandong Provincial Qianfoshan Hospital (affiliated with Shandong First Medical University) in Jinan, China, offers critical insights into how dermoscopy—an essential tool for skin cancer diagnosis—can catch ALM before it spreads.

The Case That Shed Light on Early ALM

The study focuses on a 57-year-old woman who visited the clinic with a light brown, irregularly shaped patch on her left foot. The lesion had slowly grown over five months but caused no pain or itching—common reasons people delay seeing a doctor. A physical exam revealed a 10mm × 8mm spot with mixed colors (light/dark brown, white, black, red)—a red flag for potential melanoma.

When the team used dermoscopy (a handheld device that magnifies skin lesions 10–100x), they identified several key features:

  • Parallel ridge pattern: A signature sign of ALM, where pigment follows the raised ridges of the skin (think of the “fingerprint” pattern on palms or soles).
  • Irregular diffuse pigmentation: Blotches of varying brown shades, unlike the even color of a benign mole.
  • Atypical dots and globules: Small, unevenly shaped pigmented spots.
  • Regression structures: Areas where the tumor stops growing, appearing as white or light pink patches.
  • Milk-red area and surface scaling: Features more often linked to invasive melanoma, but surprisingly present here.

Eccrine pores—tiny openings for sweat glands—also appeared as regular white dots within the pigmented bands. This helped the team rule out benign conditions like plantar warts or friction spots.

Confirming the Diagnosis: What the Lab Revealed

The lesion was surgically removed to prevent spread. Lab tests confirmed it was ALM in situ: Abnormal melanocytes (skin cells that produce pigment) were clustered in the basal layer of the epidermis (the outer skin layer) but had not invaded deeper tissues. Immunohistochemical stains—tests that detect specific proteins in cells—showed the abnormal cells were positive for HMB-45 (a marker for melanoma) but negative for S-100 (another marker, which can be absent in early-stage cases).

Why This Matters for Early ALM Detection

ALM is easy to miss because it often looks like a harmless freckle or callus. Dermoscopy changes the game:

  • The parallel ridge pattern has a 99% specificity (meaning it’s almost never seen in benign lesions) and an 84% positive predictive value (if you see it, there’s an 84% chance it’s ALM), per a 2004 study in the American Journal of Dermatopathology.
  • Irregular diffuse pigmentation (blotchy brown patches) has a 96.6% specificity, according to a 2004 multicenter study in Japan published in Arch Dermatol.

This case also revealed something new: Features like the milk-red area and surface scaling—typically linked to invasive melanoma—were present in this in situ lesion. This suggests ALM in situ may have more diverse signs than previously thought, especially in Asian populations.

The Bottom Line: Early Detection Saves Lives

Melanoma in situ is 100% curable with surgery—but only if caught early. Most dermoscopy guidelines were developed for later-stage, invasive melanoma, making in situ cases harder to diagnose. Studies like this one help fill that gap, giving doctors more tools to spot ALM before it becomes dangerous.

Who Led the Study?

The research was conducted by Fei Gao and Lin-Lin Xin, dermatologists at Shandong Provincial Qianfoshan Hospital (The First Hospital Affiliated with Shandong First Medical University). Their work was published in the Chinese Medical Journal in 2019. The patient provided full consent for her case to be shared, with steps taken to protect her identity.

What You Can Do

If you notice a pigmented patch on your hands, feet, or nails that:

  • Grows or changes shape/color
  • Has irregular borders or mixed colors
  • Causes scaling, bleeding, or itching

See a board-certified dermatologist right away. Dermoscopy could be the difference between catching ALM early or missing it until it’s too late.

References:

  1. Nufer KL, Raphael AP, Soyer HP. Dermoscopy and overdiagnosis of melanoma in situ. JAMA Dermatol. 2018;154(3):398-399.
  2. Kwon IH, Lee JH, Cho KH. Acral lentiginous melanoma in situ: a study of nine cases. Am J Dermapathol. 2004;26(4):285-289.
  3. Saida T, Miyazaki A, Oguchi S, et al. Significance of dermoscopic patterns in detecting malignant melanoma on acral volar skin: results of a multicenter study in Japan. Arch Dermatol. 2004;140(10):1233-1238.
  4. Marghoob AA, Malvehy J, Braun RP. Atlas of Dermoscopy. 2nd ed. London: Informa Healthcare; 2012:210-219.

Original study citation: Gao F, Xin LL. Dermoscopic features of acral lentiginous melanoma in situ. Chin Med J. 2019;132(17):2123-2124.
doi: https://doi.org/10.1097/CM9.0000000000000386

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