Assessment and Plan for Positive Wood's Lamp Uptake
When Wood's lamp examination reveals brick-red fluorescence after photosensitizer application, proceed with photodynamic therapy (PDT) according to established protocols for the specific lesion type being treated. 1
Understanding the Positive Finding
A positive Wood's lamp examination showing brick-red fluorescence confirms protoporphyrin IX (PpIX) accumulation in the target tissue after application of aminolevulinic acid (ALA) or methyl aminolevulinate (MAL). 1 This fluorescence detection occurs when long-wavelength ultraviolet A light (340-450 nm) from the Wood's lamp illuminates the porphyrin-enriched lesion. 1
The Wood's lamp check is performed 4-6 hours after photosensitizer application to confirm PpIX generation in at least the superficial part of the lesion before proceeding to light treatment. 1
Treatment Protocol Following Positive Uptake
For Actinic Keratoses (AK)
- Proceed with single PDT treatment using red light (630 nm) or blue light (410-450 nm) for superficial lesions. 1
- Apply light exposure 3 hours after MAL application or according to the specific ALA formulation protocol. 1
- Non-responding lesions receive a second treatment at 3 months. 1
For Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma in situ
- Administer two PDT treatments with a 1-week interval, with light exposure 3 hours after MAL application. 1
- The second treatment targets deeper portions of the tumor that may not have been reached initially. 1
- Incompletely responding lesions typically receive a second PDT cycle at 3 months. 1
Light Delivery Specifications
- Use red light centered at 630 nm for deeper penetration in BCC and SCC in situ. 1
- Blue light (410 nm peak) is appropriate for more superficial lesions like AK. 1
- Ensure the illumination field includes at least a 5-mm border around each lesion. 1
Pain Management Considerations
Apply topical anesthetic (EMLA cream) 1 hour prior to illumination (at 3-5 hours post-photosensitizer application) or provide local injected anesthesia during treatment if needed. 1 MAL-PDT causes less pain than ALA-PDT while maintaining similar efficacy. 1
Post-Treatment Instructions
- Protect the treatment site from ambient light for 24-48 hours following PDT. 1
- Document the total light dose and intensity of illumination delivered. 1
- Schedule follow-up assessment to evaluate treatment response and determine need for additional cycles. 1
Important Clinical Caveats
The British Association of Dermatologists notes that Wood's lamp fluorescence detection is "a crude technique and its relevance to clinical practice is undefined" for photodynamic diagnosis. 1 However, it remains useful for confirming superficial PpIX generation before proceeding with treatment. 1 The fluorescence primarily indicates photosensitizer accumulation in superficial tissue layers and does not guarantee adequate penetration to deeper tumor portions, which is why multiple treatment sessions are often required for thicker lesions. 1