Diagnostic Evaluation: Photographic Testing in Dermatology
Photographic tests are essential procedures used in patients with skin conditions caused or exacerbated by sun exposure (what is known as reactions.). The main objective is to achieve a specific diagnosis and define the most appropriate treatment strategy for the patient.
- Patch Tests: patch
- Photopatch tests
- Phototests
- Photoprovocation tests
- Specialized laboratory investigations
Understanding Photopatch Tests
Photopatch tests are an extension of standard patch tests. They are implemented when the dermatologist suspects an contact infection dermatitis to a specific substance, which only manifests in the presence of sunlight.
After application and subsequent removal of the patches, a small area of skin is exposed to a controlled dose of long-wave ultraviolet light (UVA). This dose, typically 5J/cm², is significantly lower than that required to induce sunburn.
Phototest Procedure and Purpose
Phototests are specialized tests designed to confirm the existence of an abnormal skin response to sun exposure. They are particularly useful when photosensitivity is induced by medication intake or in cases of chronic photosensitive dermatitis. dermatitis photosensitive chronic. Furthermore, these analyses significantly aid in the diagnosis of hives solar urticaria.
Although more advanced methods employ monochromators, these devices are not available in all regions, such as New Zealand. For the detection of abnormal sensitivity, solar simulators based on tungsten-halogen lamps and fluorescent bulbs are commonly used, allowing evaluation of the response to short-wave (UVB) and long-wave (UVA) rays.
One-square-centimeter skin areas (typically on the lower back or buttocks) are exposed to different doses of UVB and UVA. After 24 hours, these areas are evaluated to record the Minimal Erythemal Dose (MED), which represents the lowest dose of UVB and UVA capable of producing a clearly discernible pink mark.
Use of Photoprovocation Tests
Photoprovocation tests are indicated for patients with sun-triggered skin disorders, especially when the reaction to sunburn is a normal part of their physiology. The most common disorder diagnosed with this technique is rash polymorphous light eruption, although they are also key in diagnosing lesions actinic, actinic prurigo Dermatosis, juvenile spring eruption, and hydroa vacciniforme. It is important to note that a negative test result does not completely rule out these conditions.
The usual protocol involves exposing a 10 x 5 cm area of the forearm to UVB (a dose of 1.5 times the MED) using a fluorescent lamp for three consecutive days. Simultaneously, a similar area on the opposite arm is exposed to UVA light (30 J/cm2). These simulated doses are comparable to the radiation received after approximately one hour of intense midday sun exposure in summer.
On occasion, it may be necessary to previously determine the MED to UVB in an area adjacent to the test site. Exposures are generally performed on sites that have typically been affected by the rash photosensitive.
photosensitive eruption. If the characteristic rash develops, a biopsy biopsy can be performed for analysis.
Complementary Laboratory Investigations
A large number of patients will be requested to undergo blood tests, with a complete blood count and antinuclear antibody (ANA) detection being common.antinuclear antibody).
If porphyria is suspected is suspected., biochemical tests on blood, urine, and feces may be required.
The biopsies Skin biopsies can be requested if the diagnosis of the rash is unclear or if there is clinical suspicion of lupus erythematosus.
The correct interpretation of these diagnostic tests is crucial to differentiate between the various forms of photosensitivity and thus establish precise and effective dermatological management.
