PUVA

For UVA to be effective, it has to be given in combination with an oral medication called 8 meth oxypsoralen (8MOP). Natural psoralens have been used for hundreds of years in India where they have been used to treat vitiligo; their main action is to increase photosensitivity. This then makes the UVA a very effective treatment for psoriasis. Because it must be given in conjunction with an oral medication which can cause a number of side effects listed in Table 8.4, PUVA therapy is usually given if UVB has not been successful. Box 8.3 lists the possible contraindications for giving PUVA. In a similar way to the MED testing for UVB therapy, minimal phototoxic dose (MPD) is calculated for PUVA.

Table 8.4 Possible side effects of PUVA.

Box 8.3 Contraindications for giving PUVA Refusal to wear eye protection Melanoma and non-melanoma skin cancers Photosensitising medication Pregnancy Cataracts Photosensitivity disorders (e.g. lupus, albinism)

The medication is taken 1–2 hours prior to the treatment being administered. Once the 8 MOP has been taken, the individual must wear eye protection and avoid sun exposure for at least 12 hours. Sunglasses or coated normal glasses must be tested to ensure that they are preventing penetration of UV radiation. Gastrointestinal upsets can be lessened if the medication is taken with a small meal. It is advisable that each time the tablets are taken, the amount of food ingested is more-or-less the same to ensure a consistent serum level of 8 MOP. As with UVB, men should wear genital protection. A facial shield should be used if there are no facial lesions.

For those who find that 8MOP induces too many of the below acute side effects, topical PUVA may be helpful. The individual immerses themselves in a bath in which 8MOP solution is dissolved and is then exposed to the UVA in the same way. Exact protocols will vary; however, the UVA can be given immediately after the bath and there is no need to wear eye protection following treatment. Whilst serum levels of 8MOP are lower, the therapeutic benefits appear to be as good if not better during bath PUVA than oral PUVA. There also appear to be fewer side effects (Cooper et al., 2000). Bath PUVA requires more 8 MOP and is therefore more expensive; however, it remains a viable option for those who do not respond to, or who may be excluded from oral PUVA. Cost can be reduced by the use of a polyethylene sheet in the bath which reduces the amount of water that comes into contact with the skin and therefore the amount of psoralen needed to create the correct dilution (Streit et al., 1996).

Topical psoralens can also be applied to localised areas such as hands and feet when the psoriasis just affects these areas. As with bath PUVA, there are none of the acute systemic side effects with this method of treatment (except potential burning). The UVA light is then just directed at those areas using hand and foot PUVA machines.