A 35-year-old woman from Kerala presents with a 2 cm dark nodule on her sole that has been enlarging over 3 months. Dermoscopy reveals parallel ridge pattern with brown-black pigmentation. Histopathology shows melanoma with Breslow thickness of 3.2 mm and 8 mitoses per mm². Which feature BEST distinguishes acral lentiginous melanoma from superficial spreading melanoma in this patient?

Explanation

## Acral Lentiginous Melanoma vs. Superficial Spreading Melanoma: Anatomic Discriminator ### Clinical Context **Acral lentiginous melanoma (ALM)** is a distinct subtype that arises on **acral surfaces** — palms, soles, and nail beds — areas with unique dermatologic anatomy and lower UV exposure. It accounts for 5–10% of melanomas in Caucasians but up to 50% in darker-skinned populations, making it a critical diagnosis in Indian patients. ### Comparison Table | Feature | Acral Lentiginous | Superficial Spreading | | --- | --- | --- | | **Location** | Palms, soles, nail beds (acral) | Trunk, extremities (non-acral) | | **Dermoscopy pattern** | Parallel ridge, parallel furrow, fibrillar | Reticular, globular, homogeneous | | **Age at diagnosis** | Younger (40–50 years) | Older (50–60 years) | | **UV exposure link** | Weak/absent | Strong (chronic sun) | | **Breslow thickness** | Often > 2 mm at diagnosis | Often < 1.5 mm at diagnosis | | **Prognosis** | Worse (deeper, acral location) | Better (earlier detection) | | **Racial predilection** | Higher in dark-skinned, Asian populations | Higher in Caucasians | ### Key Point: **The single best discriminator is LOCATION on acral surfaces (palms, soles, nail beds) combined with the characteristic dermoscopic parallel ridge or parallel furrow pattern.** This anatomic predilection is pathognomonic for ALM and is independent of other prognostic factors. ### High-Yield: ALM on the sole (as in this case) is a classic NEET PG scenario. Remember: **acral surfaces = think ALM**. The parallel ridge pattern on dermoscopy is the diagnostic hallmark. ### Mnemonic: **ALM = Acral Location Melanoma** — if you see a melanoma on the palm, sole, or under a nail, it is ALM until proven otherwise. ### Clinical Pearl: ALM is often diagnosed at a thicker stage (Breslow > 2 mm) because acral sites are less frequently examined and the lesion may be mistaken for a benign nevus or callus. In Indian and other darker-skinned populations, ALM is relatively more common and should be actively screened for.