Random Dermatology MCQ - Melanoma Diagnosis

A 58-year-old man presents with a pigmented lesion on his upper back. He reports it has been changing in size and color over the past year. Clinical examination reveals a 7 mm asymmetrical macule with irregular borders and color variegation (tan, dark brown, and pink). Dermoscopy shows an atypical network, irregular dots/globules, and regression structures (white scar-like areas and blue pepper-like granules). Which of the following is the most likely diagnosis?

A) Solar lentigo
B) Dysplastic nevus
C) Pigmented basal cell carcinoma
D) Superficial spreading melanoma
E) Seborrheic keratosis

Correct Answer: D) Superficial spreading melanoma

Explanation

This clinical and dermoscopic presentation is highly characteristic of superficial spreading melanoma (SSM), the most common subtype of melanoma.

Key Clinical Features (ABCDE Criteria):

• Asymmetry: The lesion is asymmetrical in shape.

• Border irregularity: The borders are uneven or notched.

• Color variegation: The presence of multiple colors (tan, dark brown, pink) within a single lesion is a major red flag.

• Diameter: While often >6 mm, melanomas can be smaller, making the other features more critical.

• Evolving: The patient's report of a changing lesion is a critical historical clue.

Key Dermoscopic Features:

• Atypical pigment network: Irregular, broad, and hyperpigmented lines.

• Irregular dots/globules: Black, brown, or gray dots/globules varying in size, shape, and distribution.

• Regression structures: A combination of white scar-like areas (fibrosis) and "blue pepper-like" granules (melanin in the dermis). The presence of regression is a significant clue for invasion and is highly associated with melanoma.

• The combination of these features creates a multicomponent or chaotic pattern, which is classic for melanoma.

Why Not the Other Options?

• (A) Solar lentigo: Appears as a homogeneous, tan to brown macule with a sharply demarcated border and a moth-eaten appearance on dermoscopy. It lacks color variegation, an atypical network, and regression.

• (B) Dysplastic nevus: Can share some features with melanoma (e.g., asymmetry, ill-defined borders). However, it typically shows a more orderly and symmetric pattern on dermoscopy, such as a peripheral rim of globules or a central homogeneous area. It lacks the chaotic features and regression seen here.

• (C) Pigmented basal cell carcinoma: Dermoscopy reveals classic features like leaf-like areas, large blue-gray ovoid nests, arborizing vessels, and ulceration. It does not typically have a pigment network or regression structures.

• (E) Seborrheic keratosis: Features comedo-like openings, milia-like cysts, and a stuck-on appearance. It is sharply demarcated and does not show a network or regression.

Histopathological Correlation:
A biopsy of this lesion would be expected to show:

• Radial growth phase: Melanoma cells spreading asymmetrically along the dermo-epidermal junction as single cells and nests (pagetoid spread).

• Cytologic atypia: Melanocytes with large, hyperchromatic nuclei.

• Regression: Areas of dermal fibrosis (scarring), melanophages, and a lymphocytic infiltrate, correlating with the dermoscopic findings.

Management:
The next step is a diagnostic excisional biopsy with narrow margins to confirm the diagnosis and obtain an accurate Breslow thickness for staging.