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.