If a specific diagnosis cannot be rendered then the observer moves to the second step of the algorithm. Therefore, the second step includes lesions that are suspicious for melanoma and lesions that cannot be safely diagnosed. The latter group of morphologically equivocal tumors consists mainly of nevi that demand special attention, but also of some melanomas lacking the usual disorganized distribution of structures and colors. Consequently, the main goal of the second step is to maximize melanoma detection and, thus, all lesions entering the second step should be evaluated for the presence or absence of melanoma specific patterns and structures.
As a principle, the second step analysis should be always performed in conjunction with the overall clinical context of the lesion. This is because the diagnostic usefulness of each dermoscopic criterion for melanoma depends on the other tumors included each time in the differential diagnosis. Often, the differential diagnosis is narrowed by clinical data, since one or more diagnoses might be excluded (or considered very unlikely) based on epidemiologic characteristics of the patient (ex. age). Therefore, the dermoscopic analysis should be adjusted each time to the clinically established differential diagnosis and aim to narrow it further.
- A recently appeared pigmented macule in a 70 years old man, dermoscopically displaying regularly distributed brown dots: Regular dots are considered as suggestive of a nevus. However, the diagnosis of a nevus is not included in the clinical differential diagnosis of a pigmented lesion developing at this age. Therefore, an epidemiologic characteristic (age) narrows the differential diagnosis into 2 main possible entities: melanoma and seborrheic keratosis/solar lentigo. Between these 2 diagnoses, brown dots are strongly suggestive of melanoma.
- Atypical network is generally considered a melanoma-specific criterion. However, in a young individual with multiple atypical nevi, a degree of network atypia in a nevus might be tolerated, especially in the presence of additional nevi with similar features. Precisely the same aspect in a solitary lesion would be considered as highly suspicious.
- A pigmented lesion dermoscopically typified by regularly distributed peripheral streaks: in a child would be considered as diagnostic of Reed nevus. In an individual of 60 years the same pattern would be strongly suspicious for melanoma.
- A non-pigmented lesion dermoscopically displaying dotted vessels: In a child, the differential diagnosis would include a Spitz nevus and a viral wart. In an elderly individual, the differential diagnosis would include melanoma, intraepidermal carcinoma and lichen-planus like keratosis.