Psoriasis is a common skin disease, which affects 2-3% of the population. Up to two third of patients with psoriasis develop nail changes. These visible changes can be painful and disabling and are associated with social stigma. Most topical treatments are only partially effective. Systemic treatments can have serious side effects. Excimer laser is a form of targeted ultraviolet light therapy that has been successfully used to treat isolated psoriatic plaques on difficult to treat areas such as scalp or palms. The purpose of this study is to investigate efficacy of excimer laser for treatment of fingernail psoriasis. Sixteen patients with stable fairly symmetric fingernail psoriasis will be enrolled. After obtaining informed consent, an investigator will evaluate the severity of nail psoriasis in each hand using an objective score, called Modified Nail Psoriasis Severity Index (mNAPSI). In a random fashion, one hand will be treated with excimer laser and the other hand will receive sham treatment. During the treatments, patients will wear protective eyewear that does not permit them to see which hand receives active treatment and which hand receives sham treatment. Patients will be treated twice a week for 8 weeks. At weeks 8, 12, and16 the investigator who is blinded to the treatment assignments will re-evaluate the fingernails using mNAPSI score. Mean change from baseline mNAPSI score at weeks 8, 12, and 16 in hands treated with excimer compared to hands treated with sham will be measured. We will also measure patient's assessment of severity of nail disease and the pain or any adverse events associated with laser treatments. Given the slow growth rate of fingernails, the final evaluations will be performed at week 16. In summary, this is the first controlled study to evaluate efficacy of excimer laser in fingernail psoriasis. If found to be effective, excimer laser could be used as a safe, locally administered treatment for recalcitrant nail psoriasis.

Inclusion Criteria:

• Must give written informed consent.
• Must be at least 18 years old.
• Must have been diagnosed with stable fingernail psoriasis.
• Must have fairly symmetric fingernail psoriasis in right and left hand with similar modified NAPSI scores in right and left hand target nails. Target nail is defined as the fingernail with highest modified NAPSI score.
• Must have active fingernail psoriasis, defined as a target fingernail matrix NAPSI score of at least 2 and modified NAPSI score from a combination of crumbling, onycholysis and pitting at least 2. •
• No changes in the systemic therapy or nail directed topical therapy during the 16 week study period.

Exclusion criteria:

• Subjects unable to tolerate frequency of visits.
• History of intolerance to or worsening of psoriasis with ultraviolet light.
• Current use of known photosensitizing medications.
• History of Fitzpatrick Type I skin, photosensitivity, or keloid formation.
• Any new systemic psoriasis therapy including biologics, conventional systemic immunomodulators, phototherapy, or nail directed topical therapy for the last 3 months prior to enrollment.
• Any other condition that in the eyes of the investigator will disqualify patient from the study.

Adverse event data were collected over 16 weeks (entire time of participation for each subject from screening to termination.