Dosage

• Initial dose depends on individual’s skin type (including formal MED testing), plaque characteristics, and thickness (500-900 mJ/cm² for XTRAC*).
• Subsequent doses adjusted according to clinical response and/or side effects.

Although phototherapy has been previously used to treat localized lesions, this approach became more practical and available with the introduction of a 308-nm monochromatic xenon-chloride laser for  psoriasis in 1997.⁸⁷ Delivering a monochromatic and coherent beam of photons, excimer lasers selectively target affected lesions of psoriasis while leaving unaffected skin untreated. The chromophore for the excimer laser is cellular DNA.⁸⁸ Breakage of strands of DNA in T lymphocytes and expression of mitochondrial proteins related to cell death has been noted after exposure to the 308-nm laser.⁸⁹ After psoriatic lesions are exposed to 308-nm excimer light, there is T-cell depletion accompanied by decreased epidermal proliferation.⁹⁰ Although working on the same premise as NB-UVB, the excimer laser focuses directly on individual lesions of psoriasis and penetrates deeper into the skin where it may lead to apoptosis of reticular dermal T lymphocytes.  The excimer laser has the advantage of treating only involved skin, therefore minimizing potential risks of exposing normal-appearing skin to UV radiation. The excimer laser is, therefore, not limited by the MED, which renders this mode of UV therapy more efficacious when supra-erythemogenic doses are used.

Evidence-based studies on the dosage and scheduling of excimer laser therapy are limited. The dose of energy delivered is guided by the patients’ skin type and thickness of the plaque; further dosages are adjusted based on the response to therapy or development of side effects (Table V). Initially, most of the protocols for treatment with the 308-nm excimer laser were based on the MED, but more recently dosing according to the thickness of the plaque has become used. The frequency of treatment with the excimer laser is 2 to 3 times a week, with a minimum of 48 hours between treatments.

Duration of treatment

• Dosing 2-3 times/week until patient is clear.
• Usually average of 10-12 treatments are needed.

References

87. Bonis B, Kemeny L, Dobozy A, Bor Z, Szabo G, Ignacz F. 308 nm UVB excimer laser for psoriasis. Lancet 1997;350:1522.
88. de With A, Greulich KO. Wavelength dependence of laserinduced DNA damage in lymphocytes observed by single-cell gel electrophoresis. J Photochem Photobiol B 1995;30:71-6.
89. Novak Z, Bonis B, Baltas E, Ocsovszki I, Ignacz F, Dobozy A, et al. Xenon chloride ultraviolet B laser is more effective in treating psoriasis and in inducing T cell apoptosis than narrow-band ultraviolet B. J Photochem Photobiol B 2002;67: 32-8.
90. Bianchi B, Campolmi P, Mavilia L, Danesi A, Rossi R, Cappugi P. Monochromatic excimer light (308 nm): an immunohistochemical study of cutaneous T cells and apoptosis-related molecules in psoriasis. J Eur Acad Dermatol Venereol 2003;17:408-13.

Short-term results

• Initial response within 8-10 treatments.
• Depends on multiple factors such as device used, protocol used, lesion characteristics, and site.

Long-term results

• Mean remission times of 3.5-6 months.

An early study to assess the efficacy of the 308-nm excimer laser used high-dose therapy, 8 to 16 times the MED.⁹¹ In all, 11 of 16 patients had a greater than 75% improvement within 1 month. Even a single treatment with the excimer laser can have a beneficial effect.⁹² Because high doses of UVB administered by the excimer laser led to blistering and burning in almost half of the patients, lower doses in the range of 1 to 3 MED were subsequently used and the dosage was adjusted according to response; a greater than 95% clearance was observed with an average of 10.6 treatment sessions.⁹³ In a multicenter open-label study of 124 patients with psoriasis treated with an initial dose of 3 MED, subsequent doses were adjusted according to clinical response. In all, 84% of the patients achieved more than 75% clearance after two treatment sessions; 72% cleared at an average of 6.2 treatments.⁹⁴ In another open-label study of 120 patients with psoriasis treated with an initial dose of 3 MED followed by an increase of 1 MED per session, two thirds of patients cleared more than 90% after 10 treatments whereas 85% of patients showed a Psoriasis Area and Severity Index 90 or greater after 13 sessions with an average treatment duration of 7.2 weeks^.95 In a study of 40 patients with psoriasis, an improvement of approximately 90% was noted in patients with macular psoriasis and 77% in plaque psoriasis in an average of 13.7 treatments.⁹⁶

Although treatment with the 308-nm excimer laser can clear psoriasis, there is limited information on the duration of remission. One study suggests that the mean remission time is 3 to 4 months after cessation of therapy.^91-93 After a follow-up of 1 year, 26 of 28 patients had long-term improvement.⁹⁷ Efficacy of the excimer laser has been demonstrated in scalp psoriasis when combined with a blower device that displaces the hair interfering with the laser beam.^98-100 Palmoplantar psoriasis has also been treated with the excimer laser. In an open-label study of 54 patients with palmoplantar psoriasis, complete clearance was observed in 57% of patients; the average number of treatments required was 10 for palmar psoriasis, and 13 for plantar psoriasis.¹⁰¹

References

91. Trehan M, Taylor CR. High-dose 308-nm excimer laser for the treatment of psoriasis. J Am Acad Dermatol 2002;46:732-7.
92. Asawanonda P, Anderson RR, Chang Y, Taylor CR. 308-nm Excimer laser for the treatment of psoriasis: a dose-response study. Arch Dermatol 2000;136:619-24.
93. Trehan M, Taylor CR. Medium-dose 308-nm excimer laser for the treatment of psoriasis. J Am Acad Dermatol 2002;47:701-8.
94. Feldman SR, Mellen BG, Housman TS, Fitzpatrick RE, Geronemus RG, Friedman PM, et al. Efficacy of the 308-nm excimer laser for treatment of psoriasis: results of a multicenter study. J Am Acad Dermatol 2002;46:900-6.
95. Gerber W, Arheilger B, Ha TA, Hermann J, Ockenfels HM. Ultraviolet B 308-nm excimer laser treatment of psoriasis: a new phototherapeutic approach. Br J Dermatol 2003;149:1250-8.
96. He YL, Zhang XY, Dong J, Xu JZ, Wang J. Clinical efficacy of a 308 nm excimer laser for treatment of psoriasis vulgaris. Photodermatol Photoimmunol Photomed 2007;23:238-41.
97. Fikrle T, Pizinger K. The use of the 308 nm excimer laser for the treatment of psoriasis [in German]. J Dtsch Dermatol Ges 2003;1:559-63.
98. Taylor CR, Racette AL. A 308-nm excimer laser for the treatment of scalp psoriasis. Lasers Surg Med 2004;34:136-40.
99. Gupta SN, Taylor CR. 308-nm Excimer laser for the treatment of scalp psoriasis. Arch Dermatol 2004;140:518-20.
100. Morison WL, Atkinson DF, Werthman L. Effective treatment of scalp psoriasis using the excimer (308 nm) laser. Photodermatol Photoimmunol Photomed 2006;22:181-3.
101. Nistico SP, Saraceno R, Stefanescu S, Chimenti SA. 308-nm monochromatic excimer light in the treatment of palmoplantar psoriasis. J Eur Acad Dermatol Venereol 2006;20:523-6.

Toxicity

• Erythema
• Hyperpigmentation
• Blistering, particularly with higher doses

Drug interactions

• May need to lower dosing based on presence of photosensitizing medications (note: action spectrum of most photosensitizing medications is in UVA range)

Monitoring

• At baseline; none
• Ongoing; for efficacy and burning

References

Pregnancy/Nursing

• No studies in pregnancy or nursing mothers have been performed but expert opinion is that it is safe.

Although the use of the excimer laser has not been studied in pregnant patients with psoriasis, its targeted nature suggests that the excimer laser is unlikely to have any teratogenic effects.

Pediatric use

• No large-scale studies in children have been performed but expert opinion is that it is safe.

Data regarding the use of the 308-nm excimer laser in children for psoriasis are limited but expert opinion is that it is safe.