Confocal Microscopy

• Known in full as Reflectance Confocal Microscopy (RCM). At time of publication it is still in development phase but it shows promising results

How does it work ?

• It consists of the measurement of a reflection from a laser (monochromatic light) which reaches the dermis (Vivascope is a device brand).

When can it be used ?

• It can be used to visualize the epidermis and upper dermis. Deeper structures cannot be visualized at this time be because the laser light does not penetrate.

Is it difficult to use ?

• No, but it requires perfect knowledge of the structure of the skin (normal and pathological) as contrarily to histological slides the sections are horizontal, not vertical.
• Also, contrarily to classical histology slides, the examination is on “live” moving skin.

How do the different structures of the skin appear ?

• First of all, there is no color but a grey scale ranging from black to white.

• Reflectance from the laser is strongest for keratin and melanin which appear bright appears bright.

1. because of a higher concentration of melanin this a better contrasted image may be obtained in patients with a darker skin phototype (III and above).
2. because of a higher concentration of keratin in the Stratum Corneum of the epidermis, hyperkeratotic lesions may may to be curetted to be able to see properly.

• Reflectance of collagen is intermediate and therefore appears gray.
• On the other hand, water and air appear black as there is no reflection.

What have we learnt about basal cell carcinoma with confocal microscopy ?

• Retraction clefts around islets of carcinoma cells are NOT artefacts as they are visible with the technique.
• Alcian Blue staining on histological slides reveal the presence of mucin.

When is it particularly useful ?

• In melasma, when determining the depth of pigmentation (depigmenting creams work better when there is no deep melanin accumulation)
• In “moving” lesions

1. scabies mites (sarcoptes scabiei) are alive when lesions are active.
2. blood can be seen flowing in vascular lesions such as hemangiomas

• In metabolic/storage disorders

1. In cystinosis, crystals can be seen in the keratinocytes (Chiaverni C).

What are the limitations ?

• difficult to evaluate:

1. lymphoma (in particular for classification purposes)
2. malignant lesions (melanoma…)
3. deep structures…

• It is still not possible to evaluate non flat surfaces such as the nose, ears…

Contributors:

Dr Christophe HSU – dermatologist. Geneva, Switzerland

Source of information: Kanitakis J, Geneva University Hospital, 2012