Advanced UV Techniques for Diagnosis Flashcards
What is the MED for Polymorphic Light Eruption?
Usually Normal, Occasionally Low
What is the MED for Chronic Actinic Dermatitis?
Low or very low UVA and UVB, sometimes visible light.
What is the MED for Solar Urticaria?
Rapid reaction (minutes) which may include UVA, UVB and blue/green light sensitivity.
What is the MED for Drug-Induced Photosensitivity?
Low UVA, Normal UVB.
What is the MED for Photocontact Allergy
Normal.
What is the aim of MED testing?
Characterise a photometric response for a particular condition.
What is the spectral range of UVA?
400-315nm.
What is the spectral range of UVB?
315-280nm.
What is the spectral range of UVC?
280-100nm.
Define photo-toxicity.
An acute light-induced skin response to a photoreactive chemical.
Define photo-allergy.
An immune reaction to a chemical initiated by the formation of photoproducts.
Define photo-genotoxicity.
A genotoxic (toxic to genes) repsonse after exposure to a phot-activate chemical.
Define photo-carcinogenicity.
The potential for a chemical to promote skin tumour formation in combination with exposure to UV light.
What are the aims of a Hospital Photo-testing service?
- Objective measurement of wavelength and doses to
provoke a response. - Accurate diagnosis.
- Advice on treatment/management.
Define Erythema.
- 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.
What is the Minimal Erythemal dose?
The smallest dose required to give visible redness.
What are the characteristics of a monochromator?
- Xenon Lamp.
- High irradiance.
- Broadband spectrum.
- Range of filters.
- N=2 diffraction gratings.
- n=5(3) spectra in use.
- Flexible Delivery tube.
What does weighted irradiance account for?
Skin Erythema.
Briefly explain how MED testing is carried out.
- Set monochromator to wavelength, measure output.
- Calculate exposure time for an initial dose.
- Expose patient.
- Repeat for a range of doses.
- Repeat for a range of wavelengths.
- Read at 24hrs.
How is provocation testing different from MED testing?
- A larger area of exposure.
- Broader spectrum.
- A range of doses from sub-MEd to MED.
- May require several exposures.
Explain how photo-patch testing is performed.
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.
How is Polymorphic Light Eruption clinically diagnosed and treated?
- 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.
How is Photosensitive Eczema clinically diagnosed and treated?
- Presents as eczema on sun-exposed sights.
- Abnormal MEDs.
- Managed with avoidance.
How is Solar Urticaria clinically diagnosed and treated?
- 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.
How is Drug-Induced Photosensitivity clinically diagnosed and treated?
- Abnormal MEDs, often only responding to UVA.
- Requires replacement of drug causing reaction.
How is Photocontact Allergy clinically diagnosed and treated?
- Abnormal Photo-patch tests.
- Avoid sunscreen.
