Nail psoriasis has a high incidence amongst patients with psoriasis.It is estimated to affect 80% of psoriatic patients at some time during their lives and has a significant adverse influence on their quality of life.

Treatment of nail psoriasis is disappointing, as it is refractory to treatment, with conventional therapies often having little effect.

The characteristic lesions affecting the nail present as 'oil drop' discoloration, splinter haemorrhages, subungual hyperkeratosis, and onycholysis in the nail bed or pitting, leuconychia, erythema of the lunula and crumbling in the nail matrix.Diagnosis is customarily made by patient history and physical examination, though it may be necessary to rule out onychomycosis as a differential diagnosis.

The nail psoriasis severity index has recently been reported as a possible reproducible, objective, and simple tool for clinical assessment of psoriatic nail disease.

The modified target nail psoriasis severity index has been proposed for target nail assessment which would give a degree of gradation for each parameter of 0 to 3 (0 = none, 1 = mild, 2 = moderate, and 3 = severe) in each quadrant.The topical therapies include topical and intralesional corticosteroids , topical vitamin D3 analogues (calcipotriol) , topical tacrolimus and tazarotene[8]. The efficacy of these topical therapies in nail disease is limited mainly by the impenetrability or low penetrability of the nail and nail matrix. In patients with nail psoriasis that is resistant to topical therapies, conventional systemic therapies (e.g., phototherapy, retinoids, cyclosporine, methotrexate) have been shown to be partially effective. More recently, biological therapies (e.g., infliximab, adalimumab, alefacept, etanercept) have proven efficacy in psoriasis and psoriatic arthritis, and some are effective in treating nail disease in patients with psoriasis .

Previous study proved successful treatment of onychodystrophy using fractional carbon dioxide laser with topical steroid. Fractional Carbon dioxide laser might be an effective therapy for nail psoriasis due to its ablative ability which produce microscopic holes that perhaps improve topical drug delivery. Moreover it was hypothesized that tissue ablation and remodelling process stimulate rejuvenation of the abnormal nail bed.The investigators hypothesized that the combination of Fractional carbon dioxide laser and topical tazarotene treatment will have a higher therapeutic effect on nail psoriasis through multiple mechanism.

Inclusion Criteria:

1. Thirty patients with bilateral fingernail psoriasis will be recruited from the Dermatology Outpatient Clinic, Assiut University Hospital.
2. The diagnosis will be based upon the clinical characteristics of nail psoriasis.
3. Patients will be included after they have stopped any systemic therapy for at least 8 weeks

Exclusion Criteria:

1. pregnant or lactating woman
2. patients with history of photosensitivity.
3. Patients who discontinued or just started to receive new systemic therapy or phototherapy during the study period will be dropped from the study.