Dysplastic Nevi Dermoscopy: Diagnostic Features

Dysplastic nevi, also known as atypical moles, are melanocytic nevi with clinical and histologic features that differ from common nevi. Dermoscopy plays a crucial role in their evaluation, aiding in early detection of melanoma. This article reviews the dermoscopic features of dysplastic nevi, highlighting the diagnostic characteristics that clinicians should recognize. Understanding the dermoscopic evaluation of atypical moles is essential for accurate diagnosis and management.

The prevalence of dysplastic nevi varies among populations, and they are often considered markers for increased melanoma risk. Dermoscopy enhances visualization of structures not visible to the naked eye, allowing for better discrimination between benign and malignant lesions. Here, we delve into the patterns and clues that characterize dermoscopic features of dysplastic nevi.

Understanding Dysplastic Nevi

Dysplastic nevi are characterized by their asymmetry, irregular borders, and color variation. They often appear larger than common nevi (usually >5 mm) and may have a papular or lentiginous component. Under dermoscopy, these lesions exhibit a heterogeneous pattern. The global dermoscopic pattern often shows a reticular, globular, or mixed pattern with focal atypia.

Key dermoscopic criteria for evaluating atypical moles include:

• Reticular pattern with irregular, widened network lines and holes.
• Globular pattern with irregularly sized and distributed globules.
• Focal eccentric hyperpigmentation or hypopigmentation.
• Scar-like depigmentation or milia-like cysts.

The presence of a negative network (inverse reticular) is also noted in some dysplastic nevi. This feature appears as hypopigmented holes within a pigmented network, but it is more commonly associated with Spitz nevi and melanoma. Careful evaluation is required.

Dermoscopic Patterns and Clues

Several dermoscopic patterns have been described for dysplastic nevi. The most common is the reticular pattern, which may show a thickened network with irregular meshes. Another pattern is the globular type, where globules vary in size, shape, and color. Mixed patterns are also frequent. Additional features include:

• Peripheral reticular network with central hypopigmentation (target-like).
• Multiple milia-like cysts (horny cysts) in association with pigmented network.
• Focal or multifocal hyperpigmentation (dark brown to black areas).
• Cobblestone pattern (aggregation of globules larger than usual).

A study by Kittler et al. established diagnostic criteria for dysplastic nevi, emphasizing the importance of the network and globules. In dermoscopy of atypical nevi, the presence of a broadened network with holes and irregular outlines is a key finding.

The ABCD rule for dermoscopy (Asymmetry, Border, Color, Dermoscopic structures) can be applied but may not reliably differentiate dysplastic nevi from early melanoma. Additional algorithms like the 7-point checklist or Menzies method are helpful.

Differentiating Dysplastic Nevi from Melanoma

Differentiation between dysplastic nevi and melanoma is crucial. Dermoscopic clues that favor melanoma include the presence of atypical vascular patterns (like dotted vessels, irregular linear vessels), regression structures (scar-like depigmentation with peppering), and shiny white structures (crystalline structures). Dysplastic nevi typically lack these features.

The concept of the “ugly duckling” sign is also useful: if a lesion looks different from the majority of the patient's nevi, it warrants closer examination. In dermoscopy of atypical moles, the overall pattern is usually symmetric in terms of global pattern distribution, whereas melanoma often shows asymmetry in pattern distribution.

Dermoscopic Variants and Pitfalls

Some dysplastic nevi may mimic melanoma dermoscopically, especially those with a severe degree of atypia. Common pitfalls include:

• Eccentric hyperpigmentation – can be seen in both dysplastic nevi and melanoma; look for other melanoma clues.
• Pigmented network with holes – may be mistaken for a negative network; true negative network is more concerning.
• Regression structures – rarely seen in dysplastic nevi; if present, consider melanoma.

Another important variant is the dysplastic nevus on special sites (e.g., acral, facial, genital). These may have distinct dermoscopic features. For instance, facial dysplastic nevi often have a pseudonetwork due to follicular openings. Awareness of site-specific patterns is essential.

Online resources from DermNet NZ offer comprehensive guides on dermoscopy of atypical moles. Clinicians often search for educational materials on this topic and are encouraged to consult reliable repositories for up-to-date training.

Clinical Implications and Management

Patients with dysplastic nevi require regular skin examinations, often every 6-12 months, with dermoscopic documentation of atypical lesions. Sequential dermoscopic imaging (SDDI) is recommended for changing lesions. The decision to biopsy is based on dermoscopic suspicion, patient history, and presence of other risk factors.

In summary, dermoscopy significantly improves the diagnostic accuracy for dysplastic nevi. Recognizing the typical patterns—reticular, globular, mixed with focal atypia—helps in differentiating them from melanoma. However, caution is needed because some dysplastic nevi may display overlapping features with early melanoma. Continuous education and familiarity with dermoscopic terminology are key to mastering dermoscopy for atypical moles.

For further study, resources like DermNet NZ offer illustrative cases and detailed descriptions.