The 2-Step Dermoscopy Algorithm
The 2-step algorithm provides a structured framework for evaluating any cutaneous lesion, minimizing the risk of missing melanomas while avoiding unnecessary excisions of benign lesions.
Step 1: Is it Melanocytic?
The first step is determining if the lesion is of melanocytic origin. Look for at least one of the following specific criteria:
- Pigment Network: A honeycomb-like structure of pigmented lines (typical or atypical).
- Aggregated Globules: Round to oval pigmented structures, often at the periphery.
- Branched Streaks: Linear pigmented projections extending from the lesion edge.
- Homogeneous Blue Pigmentation: In the absence of other structures (often seen in blue nevi).
- Parallel Pattern: Specifically on the palms and soles.
If none of these are present, the lesion is evaluated as non-melanocytic (e.g., BCC, SCC, Seborrheic Keratosis, Hemangioma).
What if it's Non-Melanocytic?
Look for specific criteria for other common lesions:
- BCC: Arborizing vessels, maple leaf-like areas, spoke-wheel areas, blue-gray ovoid nests.
- Seborrheic Keratosis: Milia-like cysts, comedo-like openings, cerebriform pattern, hairpin vessels.
- Hemangioma: Red-blue lacunae.
Step 2: Is it Malignant (Melanoma)?
If the lesion is melanocytic (Step 1 is positive), evaluate it for malignancy using established algorithms like the Pattern Analysis or the 7-Point Checklist.
| Criterion (7-Point Checklist) | Score |
|---|---|
| Atypical pigment network (major) | 2 |
| Blue-white veil (major) | 2 |
| Atypical vascular pattern (major) | 2 |
| Irregular dots/globules (minor) | 1 |
| Irregular streaks (minor) | 1 |
| Irregular blotches (minor) | 1 |
| Regression structures (minor) | 1 |
Note: A score of 3 or more indicates a high suspicion for melanoma and warrants excision.