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UVA Narrowband Photo Therapies

Ultraviolet-A (UVA) is the name given to the waveband of electromagnetic radiation ranging from 320-400nm. In New Zealand there is 100 times as much UVA as UVB but it has less energy. Solar UVA contributes to sunburn (10%), sun damage and skin cancer.

UVA bulbs are used in sun beds because UVA promotes tanning but is less likely to result in erythema than UVB. However, on its own UVA is ineffective in treating psoriasis and less useful than UVB for atopic dermatitis.

UVA combined with a psoralen photosensitising agent (8-methoxypsoralen or 5-methoxypsoralen) is known as PUVA or photochemotherapy. The combination is more effective than UVB in clearing or controlling a variety of skin diseases. PUVA is available at the larger public hospitals and some private dermatologists’ offices in New Zealand for treating severe skin diseases.

A modified form of PUVA is the combination of oral or topical tripsoralen and exposure to sunlight, but this can be hazardous and is not generally recommended.

Another form of photochemotherapy combines UVB with psoralen and is known as PUVB. Narrowband-UVB combined with 8-methoxypsoralens has recently been shown to be as effective as PUVA but to date there is little experience with PUVB and it will not be considered further in this course.

PUVA units in New Zealand are full body cabinets containing 6' 100W fluorescent low-pressure mercury bulbs. UVA lamps (TL100/209R) have black markings (e.g. FS72T12BLHO). Most units have 36 or 48 bulbs, and may be the same cabinet as BB-UVB and rarely NB-UVB bulbs. Hand & foot units contain 2' bulbs.

Markings on UVA bulbs
Markings on UVA bulbs

Modern units have integrated dosimetry and the time to deliver the correct dose is automatically calculated. For older units, irradiance is checked manually prior to treatment using a specific UVA dosimeter and the treatment time for a specific dose determined according to a spreadsheet.

Hand puva
Small PUVA unit for hand/foot treatment

UVA-1 is the name given to the waveband of electromagnetic radiation ranging from 340-400nm while filtering out lower wavelengths.

  • Low dose UVA1 refers to 10-20 J/cm2 per single dose
  • Medium dose UVA1 refers to 50-60 J/cm2 per single dose
  • High dose UVA1 refers to 130 J/cm2 per single dose

The long-term risks of high dose UVA1 are uncertain so no more than 10-15 treatments per cycle and two cycles per year are recommended. It appears to be effective in severe acute atopic dermatitis, urticaria pigmentosa, scleroderma and granuloma annulare.

There are to date no UVA1 units in New Zealand.

Hand puva
Daavlin UVA1 unit

Indications for PUVA

PUVA is used for more severe long-lasting and resistant disease. Psoriasis or eczema with thick plaques or affecting palms & soles may resist UVB but respond well to PUVA. Patients may change to PUVA after a trial of UVB or commence on PUVA immediately.

As the erythema action spectrum for PUVA has a steep curve, slight increments in dose may result in severe burning. PUVA may be inadvisable for very fair skinned patients because of this risk.

Because of the greater likelihood of photoageing and carcinogenesis, PUVA should not be used in children. It is complicated treatment and should only be used in patients who are able to comprehend and comply with instructions.

Psoralen requires hepatic metabolism and renal excretion therefore should be used in great care in those with hepatic or renal disease. It is not teratogenic, but like other medications should be avoided in pregnancy if possible. It is excreted in breast milk so breast-feeding mothers should not receive PUVA.

Effect of PUVA on psoriasis Effect of PUVA on psoriasis