Reflectance confocal microscopy
RCM; in-vivo confocal microscopy; cellular-level dermoscopy
Reflectance confocal microscopy is a non-invasive imaging technique that uses a near-infrared (830 nm) laser to generate horizontal greyscale images of skin at near-cellular resolution. It bridges dermoscopy (mm-scale) and histopathology (µm-scale), allowing in-vivo cellular characterisation of melanocytic and non-melanocytic lesions to a depth of approximately 200 µm (the papillary dermis). The strongest UK evidence base supports its role in mapping the extent of lentigo maligna before staged excision, characterising ambiguous facial pigmented lesions where biopsy carries cosmetic cost, and monitoring response of superficial BCC and AK to topical therapy. UK access is currently limited to specialist centres.
Principle
- An 830 nm near-infrared diode laser illuminates the skin; refractive-index differences between cellular components generate contrast.
- Optical sectioning produces en-face (horizontal) greyscale images at near-cellular resolution.
- Depth penetration ~ 200 µm — papillary and superficial reticular dermis only; cannot image deeper tumour invasion.
- Handheld and bench-top systems available (Vivascope 3000 and 1500); imaging time ~ 10–30 minutes per lesion depending on lesion size and system.
Indications
- Lentigo maligna — mapping the extent of clinically ill-defined LM before staged excision; reduces excision number and improves margin clearance (good UK evidence).
- Ambiguous facial pigmented lesion — pigmented AK vs LM vs solar lentigo where biopsy carries cosmetic morbidity.
- Superficial BCC and AK — non-invasive monitoring during and after topical therapy (imiquimod, 5-FU, MAL-PDT).
- Selected dermoscopically equivocal lesions — particularly small early melanocytic lesions.
Imaging features
- Melanoma — atypical pagetoid cells in the epidermis, non-edged papillae, atypical junctional nests, dendritic cells, sheets of atypical cells.
- Naevi — edged papillae, regular cellular network, monomorphic round cells, well-organised junctional nests.
- BCC — dark tumour nests, peripheral palisading, increased dermal vascularity.
- Sebaceous hyperplasia — bright lobules of sebocytes with central duct.
UK access and limitations
- Available in a small number of specialist UK centres — limited service provision.
- Time-consuming — typically ~ 10–30 minutes per lesion depending on lesion size and system; requires trained dermatologist / specialist nurse.
- Steep learning curve — reading curves of months to a year for accurate interpretation.
- Depth limited to papillary dermis — cannot assess invasion depth (use histology / ultrasound).
- Cost — expensive equipment and consumables.
- Patient counselling — RCM does not yet replace biopsy; complement rather than substitute.
References
- Pellacani G et al. Reflectance confocal microscopy in the diagnosis of melanoma and ambiguous melanocytic lesions. J Eur Acad Dermatol Venereol; 2014.
- Guitera P et al. RCM for the diagnosis of facial lentigo maligna. J Invest Dermatol; 2010.
- Karponis D, Stratigos IA, Joshy J et al. Lentigo maligna: a review. Clin Exp Dermatol. 2024;49:218-225.
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