Advanced UV Techniques for Diagnosis

Question 1

What is the MED for Polymorphic Light Eruption?

Answer 1

Usually Normal, Occasionally Low

Question 2

What is the MED for Chronic Actinic Dermatitis?

Answer 2

Low or very low UVA and UVB, sometimes visible light.

Question 3

What is the MED for Solar Urticaria?

Answer 3

Rapid reaction (minutes) which may include UVA, UVB and blue/green light sensitivity.

Question 4

What is the MED for Drug-Induced Photosensitivity?

Answer 4

Low UVA, Normal UVB.

Question 5

What is the MED for Photocontact Allergy

Answer 5

Normal.

Question 6

What is the aim of MED testing?

Answer 6

Characterise a photometric response for a particular condition.

Question 7

What is the spectral range of UVA?

Answer 7

400-315nm.

Question 8

What is the spectral range of UVB?

Answer 8

315-280nm.

Question 9

What is the spectral range of UVC?

Answer 9

280-100nm.

Question 10

Define photo-toxicity.

Answer 10

An acute light-induced skin response to a photoreactive chemical.

Question 11

Define photo-allergy.

Answer 11

An immune reaction to a chemical initiated by the formation of photoproducts.

Question 12

Define photo-genotoxicity.

Answer 12

A genotoxic (toxic to genes) repsonse after exposure to a phot-activate chemical.

Question 13

Define photo-carcinogenicity.

Answer 13

The potential for a chemical to promote skin tumour formation in combination with exposure to UV light.

Question 14

What are the aims of a Hospital Photo-testing service?

Answer 14

• Objective measurement of wavelength and doses to
  provoke a response.
• Accurate diagnosis.
• Advice on treatment/management.

Question 15

Define Erythema.

Answer 15

• Redness of skin due to dilation of blood vessels.
• There is a latent period of 2-4hrs, with the maximum
  response reached by 8-24hrs.

Question 16

What is the Minimal Erythemal dose?

Answer 16

The smallest dose required to give visible redness.

Question 17

What are the characteristics of a monochromator?

Answer 17

• Xenon Lamp.
• High irradiance.
• Broadband spectrum.
• Range of filters.
• N=2 diffraction gratings.
• n=5(3) spectra in use.
• Flexible Delivery tube.

Question 18

What does weighted irradiance account for?

Answer 18

Skin Erythema.

Question 19

Briefly explain how MED testing is carried out.

Answer 19

1. Set monochromator to wavelength, measure output.
2. Calculate exposure time for an initial dose.
3. Expose patient.
4. Repeat for a range of doses.
5. Repeat for a range of wavelengths.
6. Read at 24hrs.

Question 20

How is provocation testing different from MED testing?

Answer 20

• A larger area of exposure.
• Broader spectrum.
• A range of doses from sub-MEd to MED.
• May require several exposures.

Question 21

Explain how photo-patch testing is performed.

Answer 21

12 pairs of chemical patches are applied to the patient.
1 set is exposed to the relevant light source.
Comparison of exposed and unexposed sites.

Question 22

How is Polymorphic Light Eruption clinically diagnosed and treated?

Answer 22

• Presents as a rash after several days exposure.
• Normal MEDs.
• The rash may be provoked.
• Treated using light therapy, managed with avoidance of provoking wavelength.

Question 23

How is Photosensitive Eczema clinically diagnosed and treated?

Answer 23

• Presents as eczema on sun-exposed sights.
• Abnormal MEDs.
• Managed with avoidance.

Question 24

How is Solar Urticaria clinically diagnosed and treated?

Answer 24

• Presents with immediate “weal and flare” response.
• Can be triggered with UV-A, -B, or visible light.
• An immediate response from monochromator.
• Treated with light therapy (possible), managed with avoidance.

Question 25

How is Drug-Induced Photosensitivity clinically diagnosed and treated?

Answer 25

• Abnormal MEDs, often only responding to UVA.

- Requires replacement of drug causing reaction.

Question 26

How is Photocontact Allergy clinically diagnosed and treated?

Answer 26

• Abnormal Photo-patch tests.

- Avoid sunscreen.