Solar Keratosis.

Why all the fuss over Sun Spots?

What is Solar Keratosis?

Solar Keratosis are also known as Sunspots. These rough scaly lesions on the backs of hands & forearms, face & forehead are very common in Australia! Detecting a solar keratosis is a very common outcome of a routine appointment at a Skin Cancer Clinic appointment.

Aren’t Sunspots normal?

Sunspots affect around 80% of people by the age of 60¹. Sunspots are normal-unhealthy rather than normal-healthy, but they do matter. Solar Keratosis is important for these three reasons:

  • The presence of Solar Keratosis indicates significant exposure to past ultraviolet light radiation and a higher risk of skin cancer in general.
  • Solar Keratosis may develop into an important type of skin cancer: SCC (Squamous Cell Carcinoma). Indeed, Solar Keratosis is an intraepidermal neoplasia and is one end of a continuous spectrum – from Solar keratosis to IEC (Intraepithelial Carcinoma) to SCC.
  • Solar Keratosis may appear similar to skin cancers – particularly IEC. Pigmented Solar Keratosis may appear similar to Melanoma.

Because of the risk of transition of Solar Keratosis to Squamous cell carcinoma, areas of solar keratosis are therefore generally treated. The precise risk of a specific untreated Solar Keratosis developing into SCC is not known for certain. One figure from a study suggests that there is a 10% chance that a person with 7 to 8 untreated Solar Keratoses will go onto to develop one SCC within 10 years. Research suggests that 60 to 80% of SCC arises from solar keratosis.

Some Solar Keratoses may go away on their own without any treatment other than good regular sun protection.

What does a Solar Keratosis look like?

The typical solar keratosis will be a red flat scaly area on a sun exposed area. Another way to think of them is a rough area of UV-damaged fair skin. They are often felt better than seen. They are usually less than 1cm in diameter although they may be grouped together as an almost continuous area of “field change.”

The appearances can vary hugely.  There are different subtypes depending on their clinical appearance:

Classic Solar Keratosis (as described above – flat, scaly and red). Need to differentiate from an IEC.

Hypertrophic Solar Keratosis  – These are raised from the skin (sometimes markedly raised) and covered with a thick scale on a red base. These can look similar to SCC.

Cutaneous horn – These are thin hard lesions that project up from the skin and are quite firm and often dark. Hence the term “horn” which may also be caused by SCC or a viral wart. See example.

Pigmented Solar Keratosis: found most commonly on the face and can look like a melanoma.

Actinic Cheilitis: Solar Keratosis on the lips. More common on the lower lips.

A dermatoscope may be needed to examine the lesion closely to help confirm that the lesion is a Solar Keratosis and not a skin cancer or alternative diagnosis. When there is doubt then a biopsy will be required.

What is the treatment for Solar Keratosis?

There is usually evidence of of sun damaged skin around a Solar Keratosis – the whole area  is called a “field.” The treatments may be targeted to individual Sunspots, or to a whole field. Treatment of a whole field will reduce the risk of solar keratosis appearing in those adjacent areas in the future. When in doubt, it’s generally best to treat a whole field.

There are over ten different treatment options available. To cut to the chase, the most widely used treatments are efudix and cryotherapy.

Physical treatments may be used to treat individual Solar Keratosis or whole field:

  • Efudix ® (5FU): Effective, significant side effects – redness and soreness of the skin for several weeks
  • Photodynamic Therapy (PDT):  Effective, excellent cosmetic results, generally well tolerated, expensive. Treatment period shorter than with Efudix or Aldara.
  • Imiquimod (Aldara®) : Effective, similar side effects to efudix, used less often because of maximum 5cm by 5cm treatment are
  • Picato gel ®:  short course, more expensive than efudix. The role of this new topical therapy is becoming clearer; maximum 5cm by 5cm treatment area
  • Solaraze gel ®: helps minor solar keratosis with high recurrence rate but often minimal or no side effects – it has only a small role to play

There are other topical therapies for mild solar keratosis

  • Salicyclic Acid 5% in sorbolene. Useful for reducing Scale prior to treatment. This may be bought direct from a pharmacy without prescription.
  • Retinoid Creams such as ®Adapalene and Tretinoin, though not approved by The TGA, may be helpful.

It’s also a good idea to use regular moisturizer.

Surgical treatments may be used to treat more isolated lesions:

  • Cryotherapy: Clearance of around 75%. Freeze time varies from 5 seconds for the thinnest lesions to 20 seconds for longer for thick lesions.
  • Formal Excision: When a biopsy is required to exclude, for example, squamous cell carcinoma. Stitches are required.
  • Curettage: The lesion is scraped off and heals without stitches.
  • Shave Excision: Similar to Curettage and heals without stitches.

Many regular attendees of a skin cancer clinic are familiar with Cryotherapy (freezing). The issue with cyotherapy is that it does not treat a whole field. Efudix cream, on the other hand, does treat a field but usually involves several weeks of red and inflamed skin. Aldara and Picato gel are limited by the amount of skin that can be treated at a time. None of these situations are ideal which is the reason why people often choose PDT. However, PDT is still a expensive.

There are medicare funding restrictions around Prescribing of Picato® gel & Aldara® – both require “other standard treatments (to be) inappropriate” but patients may opt to have these scripts prescribed privately.

Treatment of a whole field with cream or PDT will reduce the risk of solar keratosis appearing there in the future.

Solar Keratosis may be difficult to control in some people. The starting point at home is moisturizer, sun protection and Vitamin B3 500mg twice per day.