Dermoscopy: Basics
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Direct answer
A dermatoscope is nothing more than a handheld ten-times illuminated magnifier — contact mode with a liquid or gel interface, or cross-polarised optics that read vessels without compressing them — through which the subsurface microarchitecture of pigmented and vascular lesions becomes readable. The two-step algorithm structures everything: first decide melanocytic or not; if melanocytic, look for network, globules, streaks, homogeneous blue and, on acral skin, the parallel patterns; if non-melanocytic, name the signature — arborising telangiectasia and blue-grey ovoid nests for basal cell carcinoma, milia-like cysts and comedo-like openings for seborrhoeic keratosis, red-blue lacunes for haemangioma, central white scar-like patch with peripheral network for dermatofibroma. Melanoma announces itself through atypical network, blue-white veil, regression peppering and atypical vessels; on palms and soles, the parallel ridge pattern is melanoma until proven otherwise. In India the same lens doubles as a trichoscope settling alopecia and tinea capitis without a laboratory.
What you must remember
- Instrument physics: contact dermoscopy needs interface fluid or gel and compresses small vessels; polarised dermoscopy shows vessels faithfully and lights up shiny white streaks — knowing which mode you are in explains what you see and what vanishes.
- Step one, melanocytic markers: pigment network, aggregated globules, streaks (pseudopods and radial streaming), homogeneous blue pigmentation — any one criterion makes the lesion melanocytic and pushes you to step-two pattern analysis.
- Basal cell carcinoma signature: arborising (tree-branching) telangiectasia, blue-grey ovoid nests, leaf-like areas, spoke-wheel structures, shiny white strands and focal ulceration.
- Seborrhoeic keratosis signature: milia-like cysts, comedo-like openings, fingerprinting, moth-eaten edges and fat fingers — the mimic that must be named before it is misdiagnosed.
- Vascular dictionary: comma vessels (benign naevus), dotted and polymorphous vessels (melanoma), glomerular vessels (Bowen disease), hairpin vessels with white halo (keratinising tumours), crown vessels (sebaceous hyperplasia), lacunes (angioma).
- Melanoma red flags and screening: atypical or branched network, blue-white veil, regression peppering, atypical vessels, eccentric or multiple colours; on acral skin the parallel ridge pattern (benign acral patterns are parallel furrow, lattice-like and fibrillar); the three-point checklist — asymmetry, atypical network, blue-white structures — sends two or more positives to excision or referral.
- Indian trichoscopy workhorses: alopecia areata shows yellow dots, black dots, cadaverised and exclamation-mark hairs; androgenetic alopecia shows hair-diameter diversity above 20 per cent with miniaturised hairs; tinea capitis shows comma, corkscrew and Morse-code hairs — childhood ringworm diagnosed before potassium-hydroxide.
- Practice economics: a basic dermatoscope costs less than most investigations it replaces, and dermoscopy is now formal postgraduate curriculum in India.
Working a pigmented lesion through the algorithm
A 44-year-old farmer, Fitzpatrick type V, presents with a 9 mm pigmented back lesion changing over six months. Step one: polarised dermoscopy shows a pigment network — the lesion is melanocytic. Step two: the network is atypical — thick, variable, abruptly cut off at one edge — with an eccentric structureless blue-grey zone and scattered dotted vessels at the irregular periphery. Counting against reassurance: asymmetry in two axes, multiple colours, atypical network, structureless blue — a three-point checklist scoring three of three. The decision is excision with a margin, and histology returns a superficial spreading melanoma under 1 mm — caught early by the dermoscopic read. Contrast his second lesion — milia-like cysts, comedo-like openings, moth-eaten edge: seborrhoeic keratosis, photographed, reassured, reviewed in twelve months. Same visit, two lesions, two arms of one algorithm — the utility examiners want articulated.
Where candidates slip
The step-one failure leads: calling a basal cell carcinoma "melanocytic because it is pigmented" ignores the stepwise logic — find a melanocytic criterion or move to the non-melanocytic signatures; the BCC's arborising vessels and ovoid nests are the expected answer. The second slip is acral complacency: pigmented banding on palms or soles read as "normal acral naevus" without naming the pattern — benign lesions follow furrows, melanoma rides the ridges, and that single distinction carries the mark. Third, mode confusion: expecting to see glomerular vessels through a contact scope that has just blanched them, or hunting shiny white streaks with the wrong polarisation — instrument physics is examinable precisely because it changes what is visible. Finally, forgetting the Indian utility: comma and Morse-code hairs on a child's scaly scalp make tinea capitis a bedside answer, however much steroid creams have muddied the picture.
Frequently asked questions
What is the first step of the two-step dermoscopy algorithm?
Deciding whether the lesion is melanocytic — pigment network, globules, streaks or homogeneous blue — before applying pattern analysis.
Which dermoscopic features characterise basal cell carcinoma?
Arborising telangiectasia, blue-grey ovoid nests, leaf-like areas, spoke-wheel structures and shiny white strands with focal ulceration.
Which acral pattern suggests melanoma?
The parallel ridge pattern — melanoma tracks the ridges, whereas benign acral naevi follow furrow-based, lattice or fibrillar patterns.
What are the trichoscopy findings of alopecia areata?
Yellow dots, black dots, cadaverised hairs and exclamation-mark tapering hairs against a normal follicular background.
How does dermoscopy help diagnose tinea capitis at the bedside?
Comma, corkscrew and Morse-code-like broken hairs indicate endothrix fungal invasion, allowing same-visit diagnosis ahead of culture.