​Dermatology - Polymorphous light eruption (PMLE)

​Dermatology - Polymorphous light eruption (PMLE)
PMLE refers to a collection of diverse, unexplained, acquired, and recurring skin rashes that occur as a delayed response to exposure to UV radiation. Polymorphic light eruption (PMLE) is the prevailing form of photodermatitis, typically occurring in individuals during their third decade of life. Prevalence is higher among women compared to men, as well as among those with lighter skin. Actinic prurigo is a genetic condition found in American Indians in both North and South America.


Lesions manifest during the early spring and summer seasons, characterized by the presence of erythematous macules, papules, plaques, and vesicles. Nevertheless, in every case, the eruption consistently manifests as only one kind, most commonly papular or papulovesicular. PMLE often manifests shortly after exposure and persists for a duration of 7-10 days. Occasionally, towards the end of the summer, the eruptions cease to happen, indicating a process of solidification. The symptoms include pruritus (itching that may occur before the rash appears) and paresthesia (tingling sensation).
Abnormalities
The papular and papulovesicular forms are the most common. Plaques or urticarial plaques are far less frequent. The lesions have a color spectrum ranging from pink to red. The eruption often avoids locations that are regularly exposed (such as the face and neck) and is most commonly seen on the forearms, V area of the neck, arms, and chest. Lesions may also manifest on the face in the absence of prior sun exposure.

The diagnosis is established when there is a delayed commencement of eruption, distinctive morphology, histopathological findings that exclude lupus erythematosus, and a history of the eruption disappearing within a few days. For plaque-type polymorphous light eruption (PMLE), it is necessary to perform a biopsy and immunofluorescence investigations in order to exclude the possibility of lupus. Photo-testing involves the use of both UVB and UVA.
Test sites are regularly subjected to daily exposure of UVB and UVA radiation for a duration of 1 week to 10 days, with varying levels of UV dosage. Confirmation of the diagnosis is achieved when a PMLE-like eruption appears in the test locations of over 50% of patients. The eruption observed in the test site closely resembles the sort of Polymorphous Light Eruption (PMLE) observed in that specific patient.

Sunblocks, including high-strength UVAUVB sunscreens, may not always provide complete protection, but they should always be the initial choice. Administering systemic β-carotene at a dosage of 60 mg three times a day for a duration of 2 weeks before to exposure can potentially prevent eruptions. Similarly, using oral prednisone at a dosage of 20 mg per day, starting 2 days before exposure and continuing for 2 days during exposure, may also have a preventive effect. Administering 40 mg of intramuscular triamcinolone acetonide a few days before exposure will effectively suppress an eruption.