Sunday, January 17, 2010

LASER in dermatology



The first lasers used to treat skin conditions occurred over 40 years ago. Argon and carbon dioxide (CO2) lasers were commonly used to treat benign vascular birthmarks such as port-wine stains and haemangiomas. Although these birthmarks could be effectively lightened, a side effect was the unacceptably high rate of scar formation. In the last 20 years major advances in laser technology has revolutionised their use in the treatment of many skin conditions and congenital defects, including vascular and pigmented lesions, and the removal of tattoos, scars and wrinkles. Nowadays there is a wide spectrum of laser and light technologies available for skin resurfacing and rejuvenation.




Properties of laser light

‘Laser’ is an acronym: light amplification by the stimulated emission of radiation.
Lasers are sources of high intensity light with the following properties:
  • Monochromatic, i.e., the light is of a single wavelength
  • Coherent, i.e., the light beam waves are in phase
  • Collimated, i.e., the light beams travel in parallel
Laser light can be accurately focused into small spots with very high energy.
The light is produced within an optical cavity containing a medium, which may be a gas (e.g., argon, krypton, carbon dioxide), liquid (e.g., dye) or solid (e.g., ruby, neodymium:yttrium-aluminium-garnet, alexandrite). The process involves excitation of the molecules of the laser medium, which results in the release of a photon of light as it returns to a stable state. Each medium produces a specific wavelength of light, which may be within the visible spectrum (violet 400 through to red 700nm) or infrared spectrum (more than 700 nm).
Vascular skin lesions contain oxygenated haemoglobin, which strongly absorbs visible light at 418, 542 and 577 nm, whereas pigmented skin lesions contain melanin, which has a broad range of absorption in the visible and infrared wavebands. Infrared lasers are broadly destructive because they are absorbed by water in and between skin cells (these are composed of 70-90% water).
The aim is to destroy the target cells and not to harm the surrounding tissue. Short pulses reduce the amount that the damaged cells heat up, thereby reducing thermal injury that could result in scarring. Automated scanners aim to reduce the chance of overlapping treatment areas.

What types of lasers are there?

There are several types of lasers used in skin laser surgery. Older laser technologies such as the continuous wave (CW) lasers of CO2 and argon have been largely replaced with quasi-CW mode lasers and pulsed laser systems.
The wavelength peaks of the laser light, pulse durations and how the target skin tissue absorbs this, determine the clinical applications of the laser types.



What skin conditions can be treated with lasers?

Vascular lesions

Lasers have been used successfully to treat a variety of vascular lesions including superficial vascular malformations (port-wine stains), facial telangiectases, haemangiomaspyogenic granulomasKaposi sarcoma and poikiloderma of Civatte. Lasers that have been used to treat these conditions include argon, APTD, KTP, krypton, copper vapour, copper bromide, pulsed dye lasers and Nd:YAG. Argon (CW) causes a high degree of non-specific thermal injury and scarring and is now largely replaced by yellow-light quasi-CW and pulsed laser therapies.
The pulsed dye laser is considered the laser of choice for most vascular lesions because of its superior clinical efficacy and low risk profile. It has a large spot size (5 to 10mm) allowing large lesions to be treated quickly. Side effects include postoperative bruising (purpura) that may last 1-2 weeks and transient pigmentary changes. Crusting, textural changes and scarring are rarely seen.
The new V-beam features provide ultra-long pulse duration so greater is energy directed at the target blood vessels over a longer period of time, resulting in more uniform blood vessel damage. This reduces the purpura seen with the earlier pulse dye lasers. The addition of dynamic cooling increases comfort during treatment enabling higher fluencies (energy) to be delivered safely and effectively, so fewer treatments are required.
Vascular malformations associated with smaller more superficial blood vessels respond better to treatment than deeper larger vessels (more often arising in older individuals). It is therefore best to begin treatment early. Fading by 80% occurs after 8 to 10 treatments on average. Further treatment may be necessary if the lesion recurs.
Treatment with quasi-CW lasers also produce effective outcomes but they are may be associated with higher incidences of scarring and textural changes. The most common side effects include mild erythema, oedema, and transient crusting.
Non-laser intense pulsed light devices can also be used for treating vascular lesions.

Pigmented lesions and tattoos

Melanin-specific, high energy, QS laser systems can successfully lighten or eradicate a variety of pigmented lesions. Pigmented lesions that are treatable include frecklesand birthmarks including some congenital melanocytic naeviblue naevinaevi of Ota/Ito and Becker naevi. The short pulse laser systems effectively treat the lesions by confining their energy to the melanosomes, which are the tiny granules containing melanin inside the pigment cells. The results of laser treatment depend on the depth of the melanin and the colour of the lesion and is to some degree unpredictable. Superficially located pigment is best treated with shorter wavelength lasers whilst removal of deeper pigment requires longer wavelength lasers that penetrate to greater tissue depths. Caution is needed when treating darker-skinned people as permanent hypopigmentation and depigmentation may occur. Successfully treated lesions may recur.
Prior to any laser treatment of pigmented lesions, any lesion with atypical features should be biopsied to rule out malignancy. The treatment of congenital melanocytic naevi is a controversial issue. The long-term effect of using lasers on promoting melanoma is not known but the treatment is thought to be low risk.
The QS laser systems can selectively destroy tattoo pigment without causing much damage to the surrounding skin. The altered pigment is then removed from the skin by scavenging white blood cells, tissue macrophages. The choice of laser depends on the colour, depth and chemical nature of the tattoo ink. Two to ten treatments are often necessary. Yellow, orange and green colours are the most difficult to remove.
  • Black: QS ruby, alexandrite or Nd:YAG
  • Blue and green: QS ruby, alexandrite
  • Yellow, orange, red: QS Nd:YAG or PDL
As with other laser treatments, pigmentary and textural changes including scars may occur.

Hair removal

Lasers can be used to remove excessive and cosmetically disabling hair due to hypertrichosis or hirsutism. Laser treatments remove dark hair quickly and it may take 3 to 6 months before regrowth is evident. Several treatment cycles are required with the spacing between treatments dependent on the body area being treated. Laser treatments are less painful and much quicker than electrolysis. Complications are rare but superficial burns, pigmentary changes and even scarring may occur. Increased growth of fine dark hair in untreated areas close to the treated ones has been reported.
Suitable devices include long-pulsed ruby and alexandrite lasers, diode (810nm), millisecond Nd:YAG and non-laser intense pulsed light.

Related information

References:

  • Alexiades-Armenakas MR, Dover JS, Arndt KA. The spectrum of laser skin resurfacing: Nonablative, fractional, and ablative laser resurfacing. J Am Acad Dermatol 2008;58:719-37
  • Tanzi EL, Lupton JR, Alster TS. Lasers in dermatology: four decades of progress. J Am Acad Dermatol 2003;49:1-31
  • Cantatore JL, Kriegel DA. Laser surgery: an approach to the pediatric patient. J Am Acad Dermatol 2004;50:165-84




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