This is what I found in the coders reference. It does state psoriatic skin lesions so it doesn't look like it leaves much room for interpretation, although, I could be wrong. I just thought this info might be helpful.
96920-96922 (96920, 96921, 96922)
The physician uses a fiberoptic handpiece to deliver short pulses from a 308-nm UV-B laser for the treatment of psoriatic skin lesions. Prior to the start of treatment, the optimal dose is determined by exposing uninvolved skin to the minimal effective amount of UV-B. Once this dose is established, mineral oil is applied on the lesion to enhance penetration and reduce scattering. The physician uses the fiberoptic handpiece to irradiate the lesions by using a "painting" motion. The treatment is usually painless and does not require anesthesia. Report 96920 for a total treated area less that 250 sq cm, 96921 for a total area of 250 sq cm to 500 sq cm, and 96922 for an area larger than 500 sq cm.