Actinic prurigo in Adult
AP is a familial dermatosis affecting primarily Native Americans and persons of mixed ancestry (Mestizo) located in the Americas, mostly Central and South America. It seems to be more prevalent in dryer, warm climates above 1000 meters in altitude. There is some evidence that cohabitation with domestic and farm animals and exposure to wood smoke are separate risk factors. It has also been described in White and Asian populations. AP usually presents in childhood, with a mean age of onset prior to 10 years. There is a female preponderance of approximately 4:1 in the Americas, whereas studies indicate a higher proportion of adult-onset cases along with a male preponderance in Asian populations.
There is a strong association with the HLA-DR4 antigen (90% of cases), suggesting an autoimmune basis for AP, the most specific subtype being DRB1*0407 (60% of cases), with DRB1*0401 next most prevalent at up to 20% of cases.
AP is initiated by exposure to UV radiation, with the UVA spectrum more strongly implicated than UVB. Current evidence, including findings of eosinophils and mast cells in the dermal infiltrate of mucosal and/or skin lesions along with high levels of immunoglobulin E (IgE) correlating with disease severity, suggests that UV exposure triggers a delayed type IVb hypersensitivity response to an as yet unclassified epidermal antigen. There is an overproduction of tumor necrosis factor alpha (TNF-α) in the suprabasilar keratinocyte layer that leads to production of clinical lesions.
The hallmark symptoms of AP are intense pruritus of involved skin, with the majority of patients also experiencing oral (lip) tingling and pain. Additional ocular symptoms include photophobia and increased lacrimation.
Clinically, there are excoriated, pruriginous papules and nodules in photoexposed areas. Cheilitis and/or conjunctivitis may occur in up to 50% of patients.
In more temperate latitudes, the disease is more seasonal, with exacerbations in the spring and persisting through summer. Even in these climates, portions of the rash may persist through winter. In the more equatorial latitudes, AP is a year-round condition.
Many of those afflicted as children will spontaneously remit by late adolescence, but a chronic course persisting into adulthood is common. Cases with adult onset tend to be more chronic.
L56.4 – Polymorphous light eruption
201015007 – Actinic prurigo
- Polymorphous light eruption (PMLE) – No HLA associations; occurs later, in second and third decades of life; edematous papules and plaques appear from hours to 1-2 days after sun exposure; affects exposed skin but often spares the face due to UV exposure year-round; no mucosal involvement and not usually scarring; may improve as summer progresses.
- Solar urticaria – Lesions appear within minutes of sun exposure.
- Hydroa vacciniforme – Similar age of onset and distribution of lesions, but this is a papulovesicular eruption that evolves into a vacciniform, vesiculobullous rash that resolves over 1-2 weeks. Can have ocular symptoms and findings. More common in boys.
- Systemic lupus erythematosus – Skin biopsies, ANA, anti-Ro, and anti-La antibodies may help distinguish.
- Juvenile spring eruption – Variant of PMLE occurring on the ear helices.
- Porphyria – Check urine and serum porphyrins. See porphyria cutanea tarda.
- Prurigo nodularis
- Photoaggravated atopic dermatitis – Assess for personal and family history of atopy, predominance in flexures; should respond to usual eczema treatment.
- Lymphomatoid papulosis
- Photocontact allergy – Possibly to sunscreens. See drug-induced photosensitive reaction.