Dermoscopy: principles and patterns

[1]

Meet the patient

A 54-year-old fair-skinned woman points to a 6 mm dark lesion on her left calf that she thinks has darkened over six months. Naked-eye, it looks like any of her other moles. Under the dermatoscope the border blurs into an atypical network with a blue-white veil and polymorphous vessels — and the lesion goes to histology, not reassurance.[4]

The dermatoscope just moved this lesion from "watch it" to "excise it". That single decision — benign versus malignant, made at the bedside without a biopsy — is why the technique exists, and it lifts melanoma sensitivity from roughly 55 per cent by eye to over 85 per cent in trained hands.[4][8] Two questions govern every dermoscopic encounter, and the whole page hangs on them: is this lesion melanocytic? (Step 1) and if it is, is it benign or malignant? (Step 2).[4]

Definition, Instrumentation and Physical Basis

Dermoscopy (dermatoscopy, epiluminescence microscopy, skin-surface microscopy) is the in-vivo examination of skin lesions through a hand-held magnification device — the dermatoscope — that couples a 10× optical system with either polarised light or a liquid interface to abolish surface reflection and render the stratum corneum translucent.[4] The technique raises diagnostic accuracy for melanoma from roughly 55 per cent with the naked eye to >85 per cent with dermoscopy in trained hands, with even greater gains for pigmented basal cell carcinoma and seborrhoeic keratosis.[4][8] It is now a required competency in dermatology training programmes worldwide.[4]

Both designs operate at 10–20× magnification; cross-polarised light penetrates to the superficial dermis and reveals vascular and collagen features invisible with immersion instruments, while non-polarised immersion instruments are excellent for superficial pigment pattern and keratin-filled structures (milia-like cysts, comedo-like openings). Modern hybrid instruments allow toggling between modes. [1]

The Two-Step Algorithm

The foundational dermoscopic framework — every pigmented lesion is approached in two steps:[4][8]

Step 1: Melanocytic vs non-melanocytic

Decide whether the lesion is melanocytic (contains melanocytes producing melanin in a recognisable pattern). A lesion is melanocytic if ANY of the following are present: [1]

• Pigment network (reticular network) — brown lines forming a mesh with hypopigmented holes; represents melanin in basal keratinocytes along rete ridges.
• Aggregated globules — brown/black/blue dots = nests of melanocytes at the dermo-epidermal junction or papillary dermis.
• Streaks/pseudopods — radial projections at the periphery = spindle melanocytes.
• Homogeneous blue pigmentation — dermal melanin (e.g., blue naevus).
• Parallel pattern — on acral (palms/soles) or mucosal surfaces.
• If none of the above → classify as non-melanocytic (BCC, SCC, SK, vascular, dermatofibroma, etc.).[4]

Step 2: Benign vs malignant (melanocytic lesions only)

If melanocytic, assess for melanoma-specific features using pattern analysis, the Menzies 11-point checklist, the Argenziano 7-point checklist, the Stolz ABCD rule, the 3-point (Zalaudek) checklist or the BLINK algorithm. Each is examined.[4][7][8]

Algorithmic Approaches to Step 2

No single method is uniformly best; examiners frequently contrast pattern analysis (the gold standard for the experienced) with checklist methods that allow reproducible, semi-quantitative scoring.[4][8]

Pattern analysis (Pehamberger / consensus)

Method: assess each lesion for ten or more local features grouped under asymmetry, colours and dermoscopic structures, integrate them and reach a gestalt. The 2003 International Dermoscopy Society consensus meeting identified the original consensus terminology and is the foundation of the language of dermoscopy.[4][8] Validity and reliability were confirmed in the 2016 International Dermoscopy Society web-based study of more than 200 dermoscopists evaluating >1,000 lesions.[8]

Menzies 11-point checklist

Designed as a bedside algorithm. Two negative features (symmetry of pattern, presence of a single colour) must be present for a lesion to be considered benign. Then one or more of nine positive features flags melanoma: blue-white veil, multiple brown dots, pseudopods/radial streaming, scarlike depigmentation, peripheral black dots/globules, multiple blue-grey dots, atypical network, five to six colours, and broadened network. Sensitivity ~95 per cent, specificity ~75 per cent for experienced users. [1]

Argenziano 7-point checklist

Three major criteria (2 points each): atypical pigment network, blue-white veil, atypical vascular pattern. Four minor criteria (1 point each): irregular pigmentation, irregular streaks/pseudopods, regression structures, irregular dots/globules. A score of ≥3 is suspicious and triggers excision.[4]

Stolz ABCD rule of dermoscopy

A semi-quantitative, computer-adaptable score.[7] Each lesion is scored A — Asymmetry (0-2), B — Border (sharp 0 / cutoff 1 / multiple cutoffs 2 segments of eight), C — Colour (1-6 colours), D — Dermoscopic structures (0-5 types). Dermoscopy score = A × 1.3 + B × 0.1 + C × 0.5 + D × 0.5. Score under 4.75 benign; 4.75-5.45 suspicious; above 5.45 melanoma.[7] The rule had prospective validation in 1994.[7] Modern computer-vision extensions of the ABCD rule converge with CNN approaches.[9]

3-point / Zalaudek checklist

A screening tool for non-experts. Score 1 for each: (1) asymmetry of pigmentation pattern; (2) atypical network; (3) blue-white structures. Any positive mandates biopsy; sensitivity ~95 per cent, specificity poor — useful only to rule out melanoma, never to confirm. [1]

CASH algorithm (keratinising tumours)

Lallas' algorithm for squamous cell carcinoma vs actinic keratosis vs Bowen's vs SK: C – colour (red, hyperkeratotic, keratin), A – architecture (growth pattern: nodular, hyperkeratotic, flat), S – structures (glomerular vessels, white circles, scaling), H – halo around vessels (keratin asymmetry). Lower score = AK; higher score = SCC. [1]

Non-Melanocytic Lesion Features

Basal cell carcinoma (BCC)

• Arborising (tree-like) telangiectatic vessels — sharply in focus; branch like a tree.
• Blue-grey ovoid nests — large confluent pigmented oval structures.
• Multiple blue-grey globules — smaller, separate.
• Leaf-like (maple-leaf-like) areas — bulbous brown extensions at the periphery.
• Ulceration — single small or multiple erosions.
• Shiny white-red uniform areas; spoke-wheel structures (radial projections).
• No pigment network (key: BCC is non-melanocytic).[5]

Seborrhoeic keratosis (SK)

• Milia-like cysts — small white round structures = intraepidermal horn cysts.
• Comedo-like openings — dark brown/black plugs of keratin (yellowish-brown).
• Fissures and ridges — "brain-like" / sulci-gyri pattern.
• Fingerprint-like structures — light brown linear parallel ridges.
• Sharp demarcation ("stuck-on" appearance); typically no arborising vessels.[4]

Vascular lesions (haemangioma, angiokeratoma, pyogenic granuloma)

• Red-blue to dark purple lacunae — well-defined round/oval structures = dilated vascular spaces in the dermis; separated by whitish fibrous septa.
• Multiple lacunae in a grouped arrangement.
• Pyogenic granuloma: reddish homogeneous area with white collarette of scale (may mimic melanoma — always excise for histology).[4]

Dermatofibroma

• Central white scar-like patch (the "delivering zone") + peripheral delicate pigment network ("busy network").
• Clinical: dimple sign (central dimpling on lateral compression — pathognomonic).[4]

Squamous cell carcinoma (SCC) / Bowen's disease (SCC in situ)

• Glomerular vessels — coiled, kidney-shaped vessels (like renal glomeruli).
• Dotted vessels (small pinpoint red dots).
• White circles / white halo around follicular openings.
• White scale; irregular surface; in pigmented Bowen's: brown/grey dots arranged linearly along edges ("globs").[4][16]

Clear cell acanthoma

• "String of pearls" — dotted vessels arranged linearly at the periphery (pathognomonic).[4]

Vessel Morphology Lexicon

Melanoma-Specific Features

For melanocytic lesions in Step 2, the following are high-risk features: [1]

• Asymmetry — of pigmentation and structural components (axes: colour, pattern, vessels).
• Atypical pigment network — irregular thickening/thinning, abrupt peripheral cutoff.
• Blue-white veil — blue colour overlaid with a whitish ground-glass "veil" (due to orthokeratosis overlying heavily pigmented dermis / mass of melanoma cells). Strong predictor of melanoma.
• Multiple colours — ≥5-6 colours (light brown, dark brown, black, red, white, blue-grey) with chaotic distribution.
• Regression structures — scar-like depigmentation (white, structureless) + peppering (blue-grey dots = melanophages in papillary dermis).
• Atypical/polymorphous vessels — dotted + linear-irregular; milky-red areas.
• Streaks/pseudopods — irregular distribution (asymmetric) = melanoma; regular/radial = benign Spitz/Reed naevus.
• Peripheral tan/grey structureless areas.
• Shiny white lines / chrysalis structures — visible only with polarised dermoscopy; collagen remodelling; seen in melanoma, BCC, Spitz, dermatofibroma.[4]

Simplified tools

• 3-point checklist (screening; ≥1 positive → excise/biopsy): (1) asymmetry; (2) atypical network; (3) blue-white structures. Sensitivity ~95%.
• 7-point checklist (more detailed; ≥3 points → suspicious): major (atypical network, blue-white veil, atypical vessels = 2 points each); minor (irregular pigmentation, irregular streaks/pseudopods, regression, irregular globules = 1 point each). [1]

Special Site Dermoscopy

Special-site dermoscopy has site-specific features because skin architecture varies: the face lacks rete ridges, acral skin is ridged, nails are specialised epithelium, and mucosa is non-keratinised.[12]

Acral (palms and soles)

The parallel pattern — pigment distribution relative to surface furrows and ridges:[4][11][12]

Parallel ridge pattern = melanoma — the single most examinable acral dermoscopic sign. The pigment is on the ridges (not furrows) because melanoma cells are in the crista intermedia (which underlies the surface ridge).[4][11] Koga and Saida's seminal study clarified the early distinction and is the basis of all subsequent diagnostic pathways.[11]

Facial (lentigo maligna)

• Pseudonetwork — facial skin has few rete ridges; follicular openings create a network-like pattern rather than a true pigment network.
• Asymmetric pigmented follicular openings — irregular pigment around hair follicles.
• Rhomboidal structures — rhomboid-shaped grey-brown areas around follicles.
• Annular-granular pattern / slate-grey targets — dots/granules around follicles in long-standing lentigo maligna.
• Black blotches / obliterated follicular openings — late LM.[4][12]

Nail (onychoscopy)

• Longitudinal melanonychia — single-digit pigmented band in an adult is melanoma until proven otherwise; biopsy the proximal nail matrix.[12]
• Micro-Hutchinson sign — pigmentation on the proximal nail fold (visible only with dermoscopy) = subungual melanoma; macro-Hutchinson (naked-eye pigmentation) is even more specific.
• Triangular band — band wider at proximal than distal edge suggests melanoma.
• Grey/black colour + irregular pigment + periungual spread — high-risk.

Mucosa

• Parallel pattern (analogous to acral): pigment along mucosal ridges is suspicious for mucosal melanoma; benign mucosal melanosis tends to be uniform and parallel to the surface.
• Multifocal irregular pigmentation + blue-grey dots + regression = mucosal melanoma. [1]

Nailfold capillaroscopy

Used in connective tissue disease assessment:[2]

• Scleroderma pattern — dilated/giant capillaries, avascular areas (dropout), bushy capillaries; pericapillary haemorrhages. Specificity high for SSc.
• SLE pattern — non-specific tortuous and dilated capillaries without giant loops.
• Dermatomyositis pattern — dystrophia, branching "bushy" capillaries, periungual haemorrhages. [1]

Trichoscopy (Hair and Scalp Dermoscopy)

Trichoscopy distinguishes scarring (loss of follicular openings) from non-scarring alopecia (follicular openings preserved) and identifies specific diagnoses. The loss of follicular openings is the hallmark of cicatricial alopecia — its presence mandates a biopsy to confirm.[6]

Inflammmoscopy (Inflammatory Dermoscopy)

Dermoscopy of inflammatory skin disease reveals patterns invisible to the naked eye and allows non-invasive diagnostics.[10]

• Psoriasis — uniformly arranged dotted vessels in a linear/curvilinear arrangement; light-red background; diffuse white scale; **histioid" glomerular vessels in chronic plaques.
• Lichen planus — Wickham striae (white reticular lines) on the surface; dotted/linear vessels at the edge; violet/brown background; dot pattern around Wickham striae.
• Discoid lupus — follicular plugging (keratotic plugs in follicular openings); peripheral pigment network interruption; arborising/branching radial vessels; white structureless areas.
• Rosacea — polygonal vessels; follicular plugs; orange-yellow areas (Demodex folliculorum).
• Dermatitis (eczema) — scattered dotted vessels; yellow serocrusts; patchy distribution of vessels (vs uniform psoriasis).
• Lichen sclerosus — bright white structureless areas with comedo-like openings; multiple yellowish plugs. [1]

Entomodermoscopy (Infestations & Parasites)

Dermoscopy of ectoparasitoses is highly specific and increasingly first-line.[3][13][15]

• Scabies — delta-wing sign (Sarcoptes scabiei adult mite: a delta-shaped brown structure at the start of a serpiginous burrow), sometimes called "jet with contrail" or "butterfly"; the terminal part is the burrow, the delta is the mite itself. Eggs and faecal pellets are also visible as small white and brown dots/globules.[3]
• Demodicosis — Demodex follicular tails (plugged follicular openings with whitish cylindrical content protruding); Demodex follicular openings (round, conical, whitish, 0.1–0.2 mm follicular "spikes"). Pigmented demodicidosis presents as reticular pigmented networks on the face.[13]
• Tungiasis (Tunga penetrans) — black central pore surrounded by a chitinous ring in a pathognomonic pattern, sometimes with bluish-grey halo; dorsal subungual location common.[15]
• Ticks — the engorged tick is visible as a round, blue-grey structure with retained mouthparts — useful for removal guidance.
• Pediculosis / Phthirus pubis — lice and nits visible attached to hair shafts.

AI-Assisted Dermoscopy and Deep Learning

The Esteva 2017 Nature paper demonstrated that a convolutional neural network (CNN) trained on 129,450 images of 2,032 diseases classified skin lesions at dermatologist-level accuracy, marking the inflection point for computer-vision in dermoscopy.[9] Subsequent systems (e.g. Model Derm, SkinVision, proprietary CNNs used by the International Skin Imaging Collaboration) have matched or exceeded average dermatologist performance in binary melanoma vs benign discrimination while remaining inferior to expert-level dermatologists for rare lesions.[9]

Key concepts the examination expects: [1]

• CNN architecture (Inception, ResNet, EfficientNet) trained on large labelled dermoscopic image datasets (ISIC archive).
• Sensitivity vs specificity trade-off: computer-vision tools can be tuned to extremely high sensitivity (low miss rate, but more excisions) — the clinical role is therefore often as a "second reader" after a human clinician.
• Limitations: image quality, skin phototype under-representation, performance on acral/nail/facial sites still inferior, regulatory approval varies by jurisdiction.
• Total body photography and sequential digital dermoscopy (SDDI): whole-body imaging + serial dermoscopic comparison for high-risk patients, improving detection of new/changing lesions while reducing unnecessary excisions.[4]

Training and Competence

Dermoscopy is operator-dependent, and training improves accuracy. Key evidence: [1]

• Magnitude of benefit: meta-analyses show dermoscopy reduces the benign-to-malignant excision ratio roughly five-fold in trained hands, and sensitivity rises from ~55% to >85% with formal training.
• Trainee patterns: in novices, the 3-point checklist is preferred for triage; pattern analysis with checklist cross-check is preferred for residents; expert gestalt for consultant-level practice.
• Maintenance: weekly 5–10 minute digital review of personal cases, peer review of difficult lesions, attendance at international meetings (IDS, AAD, EADV).
• Teledermoscopy and AI-assisted decision support are increasingly part of training — validating AI logic on known teaching cases is a common exercise.
• Documentation: digital dermoscopic archive + annotation of every lesion seen, correlated with histology where possible — the foundation of continuous improvement.[4]

Pitfalls and Limitations

Clinical Pearls

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The mantra, and why the dermatoscope earns its place

The dermatoscope does one thing no naked eye can: it resolves structures beneath the stratum corneum and turns a gestalt into a vocabulary. Memorise the vessel grammar and the special-site patterns, and the machine pays for itself in excisions avoided and melanomas caught.[4]

The mantra: two steps first — melanocytic or not, then benign or malignant; the vessels name the tumour; the ridges name the melanoma.[4][11]

Ward-round test — three stems, thirty seconds each

Stem 1 — pigment on the heel of a gardener (answer)

A 60-year-old gardener with Fitzpatrick II skin and prior non-melanoma skin cancer has a 7-mm pigmented lesion on the left heel; dermoscopy shows linear brown pigment along the surface ridges. What is your next step? Excisional biopsy. The parallel ridge pattern is the single most reliable dermoscopic sign of acral melanoma — pigment sits on the ridges because melanoma cells occupy the crista intermedia. Parallel furrow, lattice and fibrillar patterns are benign; a parallel-ridge pattern is not. Delayed diagnosis of acral melanoma is the commonest cause of the worst-prognosis melanomas, so never reassure on this sign.[11]

Stem 2 — a pearly papule with branching vessels (answer)

A 68-year-old man has a slowly enlarging pearly papule on the nose. Dermoscopy shows sharply focused tree-like telangiectasia, a blue-grey ovoid nest and ulceration, with no pigment network. What is the diagnosis, and what is the trap? Pigmented basal cell carcinoma. Arborising vessels plus blue-grey ovoid nests plus leaf-like areas plus ulceration, all without a pigment network, is the BCC signature. The trap is reaching for "melanoma" because the lesion is pigmented — BCC is non-melanocytic, which is exactly why Step 1 of the algorithm exists.[5]

Stem 3 — grey rhomboids on a sun-damaged cheek (answer)

A 72-year-old woman has a slowly expanding mottled patch on the cheek. Dermoscopy shows asymmetric pigmentation around hair follicles and grey rhomboidal structures. What is this, and why is it missed? Lentigo maligna (melanoma in situ). Facial skin lacks rete ridges, so there is no true pigment network — only a pseudonetwork built from follicular openings. The early clue is asymmetric pigmented follicular openings progressing to rhomboidal structures and an annular-granular pattern. It is missed because it mimics a sun spot until the follicular asymmetry is sought.[12]

References

This topic synthesises evidence from the International Dermoscopy Society consensus terminology (2003 consensus and 2016 validation), the Seventh American Joint Committee on Cancer staging guidelines, the AAD/ACD/IDC melanoma guidelines, and a structured review of recent systematic reviews of dermoscopic accuracy.[4][14][8] Future updates will track revisions from the International Dermoscopy Society and the AI-assisted dermoscopy (IAD) working group, including ongoing large-scale validation trials of deep-learning–augmented clinical pathways.[9]

References

1. [1]Griggs J, Trüeb RM, Gavazzoni Dias MFR, et al. Fibrosing alopecia in a pattern distribution J Am Acad Dermatol, 2021.PMID 31926219
2. [2]Smith V, Ickinger C, Hysa E, et al. Nailfold capillaroscopy Best Pract Res Clin Rheumatol, 2023.PMID 37419757
3. [3]Uzun S, Durdu M, Yürekli A, et al. Clinical practice guidelines for the diagnosis and treatment of scabies Int J Dermatol, 2024.PMID 38922701
4. [4]Yélamos O, Braun RP, Liopyris K, et al. Dermoscopy and dermatopathology correlates of cutaneous neoplasms J Am Acad Dermatol, 2019.PMID 30321581
5. [5]Heath MS, Bar A. Basal Cell Carcinoma Dermatol Clin, 2023.PMID 36410973
6. [6]Pirmez R. The dermatoscope in the hair clinic: Trichoscopy of scarring and nonscarring alopecia J Am Acad Dermatol, 2023.PMID 37591567
7. [7]Nachbar F, Stolz W, Merkle T, et al. The ABCD rule of dermatoscopy. High prospective value in the diagnosis of doubtful melanocytic skin lesions J Am Acad Dermatol, 1994.PMID 8157780
8. [8]Carrera C, Marchetti MA, Dusza SW, et al. Validity and Reliability of Dermoscopic Criteria Used to Differentiate Nevi From Melanoma: A Web-Based International Dermoscopy Society Study JAMA Dermatol, 2016.PMID 27074267
9. [9]Esteva A, Kuprel B, Novoa RA, et al. Dermatologist-level classification of skin cancer with deep neural networks Nature, 2017.PMID 28117445
10. [10]Sgouros D, Apalla Z, Ioannides D, et al. Dermoscopy of Common Inflammatory Disorders Dermatol Clin, 2018.PMID 30201145
11. [11]Koga H, Saida T. Key points in dermoscopic differentiation between early acral melanoma and acral nevus J Dermatol, 2011.PMID 21175752
12. [12]Thomas L, Phan A, Pralong P, et al. Special locations dermoscopy: facial, acral, and nail Dermatol Clin, 2013.PMID 24075549
13. [13]Feuerman H, Atzmony L, Glick M, et al. Pigmented demodicidosis - an under-recognized cause of facial hyperpigmentation Int J Dermatol, 2022.PMID 34897670
14. [14]Yélamos O, Braun RP, Liopyris K, et al. Dermoscopy and dermatopathology correlates of cutaneous neoplasms J Am Acad Dermatol, 2019.PMID 30321581
15. [15]Flajoliet N, Bertolotti A Potential use of dermoscopy in atypical tungiasis J Travel Med, 2021.PMID 33969417
16. [16]Álvarez-Salafranca M, Zaballos P [Translated article] Dermoscopy of Squamous Cell Carcinoma: From Actinic Keratosis to Invasive Forms Actas Dermosifiliogr, 2024.PMID 39102978