Dermatoscopy Techniques: A Comprehensive Guide for Clinicians

Introduction to Dermatoscopy Techniques

Dermatoscopy, also known as dermoscopy, is a non-invasive diagnostic technique that allows clinicians to visualize subsurface skin structures not visible to the naked eye. The basic principle involves using optical magnification and specialized lighting to examine skin lesions through either contact or non-contact methods. The technique works by reducing surface reflection and enhancing transparency of the epidermis, enabling visualization of morphological features in the epidermis, dermoepidermal junction, and papillary dermis. A dermatoscopio professionale typically offers magnification between 10x to 20x, with some advanced models providing even higher resolution. The examination requires proper preparation of both patient and equipment to ensure accurate results. Patients should be informed about the procedure and positioned comfortably to minimize movement. The skin area should be clean and free from cosmetics or ointments. For the equipment, clinicians must ensure the dermatoscope is properly calibrated, charged, and cleaned according to infection control protocols. In Hong Kong, where skin cancer incidence has risen by approximately 30% over the past decade according to the Hong Kong Cancer Registry, proper dermatoscopy technique has become increasingly important in early detection efforts.

Immersion Dermatoscopy

Immersion dermatoscopy involves applying a liquid interface between the skin and the dermatoscope to eliminate air gaps that cause light refraction. The selection of appropriate immersion fluid is crucial for optimal imaging. Commonly used fluids include:

• Ultrasound gel: Most commonly used due to its optimal viscosity and transparency
• Alcohol-based solutions: Provide good optical properties but may cause skin irritation
• Mineral oil: Excellent optical qualities but can be messy to use
• Water: Readily available but suboptimal due to rapid evaporation

The technique for applying immersion fluid requires systematic approach. A small amount of fluid should be applied directly to the lesion or to the dermatoscope's plate. The dermatoscope is then gently placed on the skin without applying pressure that might distort vascular structures. The fluid should form a continuous layer without air bubbles. The advantages of immersion technique include enhanced visualization of certain structures like blue-white veil and improved clarity of vascular patterns. However, disadvantages include potential messiness, possible allergic reactions to fluids, and the necessity of cleaning after each use. The immersion method is particularly valuable when using non-polarized dermatoscopio professionale devices that require fluid interface for optimal performance.

Non-Immersion Dermatoscopy

Non-immersion dermatoscopy, typically performed with polarized devices, does not require direct contact or fluid interface between the instrument and skin. The technique for using non-polarized light involves maintaining the dermatoscope slightly above the skin surface (typically 1-2 cm) while ensuring stable positioning to avoid motion blur. Modern dermatoscopio polarizado devices utilize cross-polarized filters that eliminate surface reflection without physical contact. The advantages of this approach include no need for messy fluids, reduced risk of cross-contamination, ability to examine moist or irregular surfaces, and preservation of vascular patterns that might be compressed with contact methods. Disadvantages include potential glare from very reflective surfaces, slightly reduced resolution compared to immersion techniques in some cases, and higher cost of polarized equipment. In Hong Kong's humid climate, non-immersion techniques are particularly valuable as they avoid the discomfort of cold gels and allow examination of perspiring skin without image degradation.

Dermatoscopy Patterns and Structures

Recognizing dermatoscopic patterns and structures is fundamental to accurate diagnosis. The pigment network appears as a grid-like pattern of brown lines surrounding hypopigmented holes, representing melanin in rete ridges. Its regularity, distribution, and thickness provide diagnostic clues. Globules are round to oval structures representing nests of melanocytes or pigmented keratinocytes, appearing as well-defined brown-black structures. Their size, distribution, and color are important diagnostic features. Dots are small, round structures smaller than globules, representing melanin at different levels of the skin. They can be black, brown, blue, or red (representing hemorrhage).

Streaks are linear structures of variable length that can be regular or irregular. They include pseudopods (finger-like projections at lesion periphery) and radial streaming (broader streaks). Regression structures represent areas of previous tumor invasion that have undergone fibrosis and melanosis, appearing as white scar-like areas (fibrosis) and blue-gray pepper-like granules (melanosis). Vascular structures provide crucial diagnostic information and include:

Proper interpretation requires understanding how these structures combine in different lesions, which is where a high-quality dermatoscopio professionale becomes essential.

Diagnosing Different Skin Lesions with Dermatoscopy

Dermatoscopy significantly improves diagnostic accuracy for various skin lesions. For melanoma, dermatoscopy reveals specific patterns depending on the subtype. Superficial spreading melanoma often shows atypical pigment network, irregular streaks, and multiple colors. Nodular melanoma may exhibit blue-white veil, atypical vessels, and structureless areas. The ABCDE criteria (Asymmetry, Border irregularity, Color variation, Diameter >6mm, Evolution) should be combined with dermatoscopic findings. Basal cell carcinoma typically shows leaf-like areas, large blue-gray ovoid nests, spoke-wheel areas, ulceration, and arborizing vessels. The absence of pigment network is also characteristic.

Squamous cell carcinoma exhibits different features depending on its differentiation. Well-differentiated lesions show hairpin vessels, scale, and white circles, while poorly differentiated ones may have linear irregular vessels and erosions. Actinic keratosis, a precursor to squamous cell carcinoma, typically shows a strawberry pattern with erythema and scale surrounding hair follicles. Seborrheic keratosis displays multiple classic features including milia-like cysts (white-yellow round structures), comedo-like openings, fissures and ridges, and hairpin vessels with white halos. Nevi show remarkably diverse patterns depending on their type. Junctional nevi typically display regular pigment network, compound nevi show globular or homogeneous patterns, and dermal nevi often exhibit comma vessels and structureless pattern. In Hong Kong, where the incidence of melanoma, while lower than Caucasian populations, has been increasing at approximately 4% annually according to Hong Kong Dermatology Society data, these differentiation skills are increasingly important.

Common Pitfalls and How to Avoid Them

Despite its diagnostic advantages, dermatoscopy has several potential pitfalls that clinicians must recognize. Artifacts and false positives can arise from multiple sources including:

• Inadequate cleaning of the lens or skin surface
• Excessive pressure applied during contact dermatoscopy
• Air bubbles in immersion fluid
• Hair covering the lesion
• Reflection from skin surface oils

Recognizing difficult lesions requires understanding that some benign lesions can mimic malignancy and vice versa. For example, regressing nevi can show blue-white structures resembling melanoma, while amelanotic melanoma might lack typical pigment patterns. Spitz nevi in children can exhibit alarming features like dotted vessels and streaks. The key to avoiding misdiagnosis is comprehensive evaluation using multiple criteria rather than relying on single features. The importance of clinical correlation cannot be overstated—dermatoscopic findings must always be interpreted in the context of patient history, lesion history, clinical appearance, and location. A dermatoscopio polarizado of high quality can help minimize some artifacts, but clinician experience remains paramount. When in doubt, documentation with digital dermatoscopy for monitoring or referral for expert opinion represents prudent practice. In Hong Kong's medical system, where follow-up care is generally accessible, this conservative approach helps prevent both over-treatment and missed diagnoses.