Polymorphous light eruption in Adult
PMLE is most commonly seen in women with lighter skin phototypes aged 20-30 years, but it can occur in all sexes, ages, and ethnicities. Worldwide, prevalence is estimated to be from 10%-20%, with higher rates in higher altitudes and in Western countries. In a 2023 study of 844 patients, a significant proportion of individuals had darker skin phototypes, and further studies that elucidate prevalence in darker skin are needed.
The etiology of PMLE is not well understood. One theory is that UVR modifies antigens in the skin of PMLE patients to make them immunogenic. There are also data to suggest that PMLE involves a type IV delayed-type hypersensitivity reaction. The action spectrum for PMLE is UVA in most cases, but UVB and both UVA and UVB may also incite the response. Recent studies have shown that PMLE is associated with mutations in the NOD2 and TLR5 genes.
Although the condition frequently recurs, the tendency toward the development of PMLE and the severity of the eruption diminish with repeated sunlight exposure. This phenomenon is termed "hardening." As the summer proceeds, it has been observed that the incidence of new eruptions decreases. Prophylactic phototherapy supports this concept of hardening or tolerance.
Despite the variability of presentations, individual patients tend to experience the same clinical manifestations with each episode.
L56.4 – Polymorphous light eruption
238525001 – Polymorphous light eruption
Differential Diagnosis & Pitfalls
- – Check for circulating antinuclear antibodies (ANA) and other associated lupus antibodies; direct immunofluorescence will be positive; skin lesions can be located on sun-exposed and sun-protected areas (in contrast to PMLE, which is primarily in sun-exposed sites).
- – Shorter time to onset of eruption with urticarial plaques lasting 1-2 hours.
- – Characteristic target lesions; systemic symptoms are prominent (in contrast to PMLE, where fever, malaise, nausea, and headache are rare).
- – Will have abnormal porphyrin profile (elevated urine uroporphyrin and stool isocoproporphyrin).
- – Lesions are very painful, and there is an elevated red blood cell protoporphyrin concentration.
- – Investigate for drug history; not seasonally associated and does not improve over time.