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Polymorphous light eruption in Adult
Other Resources UpToDate PubMed

Polymorphous light eruption in Adult

Contributors: Ruth X. Wang MD, PhD, Jeffrey M. Cohen MD, Belinda Tan MD, PhD, Susan Burgin MD
Other Resources UpToDate PubMed

Synopsis

Polymorphous light eruption (PMLE), or polymorphic light eruption, is a common acquired cutaneous disorder characterized by a pathological response to ultraviolet radiation (UVR). Erythematous papules, vesicles, and plaques (hence the name "polymorphous") develop minutes to hours after exposure to UVR, such as from sunlight or a tanning bed. The eruption is often pruritic, nonscarring, and photodistributed. Attacks most commonly occur during the spring and early summer months, especially after the first sun exposure of the season, and disappear during the winter. Systemic symptoms (such as fever, malaise, headache, myalgias, and arthralgias) are usually absent. While the eruption can last up to several weeks, most cases resolve within several days.

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.

Codes

ICD10CM:
L56.4 – Polymorphous light eruption

SNOMEDCT:
238525001 – Polymorphous light eruption

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Systemic lupus erythematosus – 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).
  • Sunburn
  • Solar urticaria – Shorter time to onset of eruption with urticarial plaques lasting 1-2 hours.
  • Erythema multiforme – Characteristic target lesions; systemic symptoms are prominent (in contrast to PMLE, where fever, malaise, nausea, and headache are rare).
  • Hydroa vacciniforme
  • Porphyria cutanea tarda – Will have abnormal porphyrin profile (elevated urine uroporphyrin and stool isocoproporphyrin).
  • Protoporphyria – Lesions are very painful, and there is an elevated red blood cell protoporphyrin concentration.
  • Drug-induced photoallergic reaction – Investigate for drug history; not seasonally associated and does not improve over time.
  • Drug-induced phototoxic reaction
  • Lichen nitidus
  • Chronic actinic dermatitis
  • Allergic contact dermatitis
  • Drug-induced Pseudoporphyria

Best Tests

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Management Pearls

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Therapy

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References

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Last Reviewed:06/20/2023
Last Updated:07/18/2023
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Polymorphous light eruption in Adult
A medical illustration showing key findings of Polymorphous light eruption : Erythema, Pruritus, Sun-exposed distribution, Smooth papules
Clinical image of Polymorphous light eruption - imageId=766208. Click to open in gallery.  caption: 'Multiple erythematous papules and papulovesicles on the dorsal hand and forearm.'
Multiple erythematous papules and papulovesicles on the dorsal hand and forearm.
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