Dermatoscopy

Key points:

- Skin cancer is common in Australia and GPs need to be competent in assessing skin lesions.

- The use of a dermatosope in clinical practice has been shown to increase diagnostic accuracy and is considered the standard of care in assessing patients with pigmented skin lesions.

- All visible lesions that cannot be confidently diagnosed should be examined with a dermatoscope.

- Dermatoscope is more than a magnifying lens and light source. By eliminating reflection from the skin surface, the dermatoscope allows better visualisation of the patterns formed by pigment and blood vessels - critical features in the diagnosis of skin lesions. (Try to get one if you don't have one already)

- There are many different methods in analysing a pigmented lesions. (CASH, the ABCD method of dermatoscopy, the 7-point checklist, the Menzies method, the 3 point checklist, the revised pattern analysis and a short modification of revised pattern analysis called 'chaos and clues'.

- The method I learned is called Chaos and Clues.

- First, we need to learn how to describe pigmented structures, which are objectively defined using the following geometric terms:

• Line: a two dimensional continuous object with length greatly exceeding with 
• Pseudopod: a line with a bulbous end
• Circle: a curved line equidistant from a central point
• Clod: any well circumscribed, solid object larger than a dot; clods may take any shape
• Dot: an object too small to have a discernible shape 
• Lines are further classified into 5 types: reticular, branched, parallel, radial and curved, as these have diagnostic significance

- Blood vessels can be described the same way:

- Colour has great diagnostic significance in dermatoscopy. The main pigments are melanin and haemoglobin, and the colours produced are shown :

- The chaos and clues algorithm:

• The first step is to dermatoscopically assess the pigmented lesion for 'chaos', defined as asymmetry of structure or colour'. Chaos is assessed by pattern not shape. As perfect symmetry is biologically rare, some deviation from geometrical symmetry must be expected. It is helpful to imagine a piece of carpet that can be cut in any shape but which maintains uniform pattern.  It would be regarded as having no chaos regardless of how irregular the shape was and regardless of the presence of a little dust on one part. 
• If chaos are identified, look for clues. 
• As for all the algorithms, there are always exceptions: beware of dermatoscopic grey on head or neck, pigmented nodular lesions, parallel ridge pattern (palms or soles)

- As with many things in life, they don't come easily. It takes a lot of time to practice, practice and practice. If in doubt, do a biopsy. (Spoke to a surgeon in the past, he told me that he has never regretted taken out a normal appendix but he always regret on the ones which he didn't. Biopsy rarely results in major harms but melanoma kills.)

Reference:

1. Dermatoscopy in routine practice 'Chaos and Clues'. Australian Family Physician. 2012.