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Actinic prurigo: ( Synonyms: hereditary polymorphic light eruption of American Indians, Hutchinson summer prurigo, photodermatitis in North American Indians)
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
Actinic prurigo (AP) is a distinct photodermatosis, diagnosed on the basis of characteristic clinical features and supported by phototest results and human leukocyte antigen (HLA) typing. It has a perennial nature, although it tends to be worse in the sunnier months in countries with seasonal variation in sunlight exposure. Morphologically, it presents as a papular or mixed papulovesicular eruption during acute flares, persistent eczematized nodules, and/or dermatitic patches, scarring, dorsal nose involvement, cheilitis, and conjunctivitis. Exposed skin tends to be more severely affected than unexposed skin, but it is not unusual for covered areas, such as the buttocks, to be involved. Abnormal photosensitivity (to ultraviolet A [UVA], ultraviolet B [UVB]) is frequently severe, but when onset has been in childhood, the condition generally gradually improves, probably largely by patients learning to adapt to their photosensitivity.
Management Strategy
Diagnosing AP requires a high index of suspicion for the general dermatologist. Differential diagnoses include severe polymorphic light eruption and photoaggravated atopic dermatitis. Although differences between European and Amerindian forms of AP have been described, these are either closely related conditions or the same disease with some differences affected by population and environment. Full phototesting and HLA typing is needed to confirm the diagnosis and establish the severity of the photosensitivity. Photopatch testing may reveal coexisting sunscreen allergies and help guide the choice of suitable sunscreens.
Once the diagnosis is established, initial management consists of advice on photoprotective measures (behavioral, clothing, and sunscreen use) and the use of potent or very potent topical corticosteroids for acute flares . Topical tacrolimus can also be considered, especially if prolonged treatment to the face is required. This approach alone is often insufficient. Some patients may benefit from the addition of a springtime course of narrowband (TL-01) UVB or psoralen-ultraviolet A (PUVA) phototherapy to enable skin hardening. When phototherapy is administered for this indication, only normally photoexposed sites need be treated. It is helpful to apply a potent topical steroid to the treated areas immediately after each exposure to reduce the risk of AP flares.
In the UK, systemic treatment is sometimes required. Thalidomide is usually effective, but its value is restricted by teratogenicity and the risk of irreversible peripheral neuropathy; antimalarials and β-carotene are of doubtful value. Pentoxifylline has anti-tumor necrosis factor (TNF)-α effects and, although listed as a third-line therapy here, may sometimes be worth considering before thalidomide because of its more attractive safety profile. Elevated serum immunoglobulin E (IgE) levels have been associated with moderate-to-severe clinical AP, suggesting involvement of the Th2-mediated inflammatory pathway. This was successfully targeted by dupilumab in a case report of a pediatric patient and raises the possibility of treatment with biologics for refractory cases in the future.
Phototesting may reveal reduced erythemal thresholds on monochromator testing. Typical lesions are sometimes provoked with UVA or solar simulator. Up to 60% of white Caucasian AP patients may carry the HLA-DRB1 ∗ 0407 subtype, but this may be negative in 40% and diagnosis may need to be supported by clinical and other phototest findings.
Actinic prurigo—a specific photodermatosis?
Addo HA, Frain-Bell W. Photodermatology 1984; 1: 119–28.
This study showed that almost 60% of AP patients have abnormal delayed erythema on monochromator phototesting.
Phototest abnormalities tend to be more severe in AP than in polymorphic light eruption.
Actinic prurigo among the Chimila Indians in Colombia: HLA studies
Bernal JE, Duran de Rueda MM, Ordonez CP, et al. J Am Acad Dermatol 1990; 22: 1049–51.
In this population, the HLA class I antigen Cw4 was more frequent in AP patients than in controls.
HLA-DR4 may determine expression of actinic prurigo in British patients
Menage H du P, Vaughan RW, et al. J Invest Dermatol 1996; 106: 362–7.
Actinic prurigo and HLA-DR4
Dawe RS, Collins P, O’Sullivan A, et al. J Invest Dermatol 1997; 108: 233–4.
An even stronger association with the HLA class II antigen HLA-DR4 was shown and, more specifically, with HLA-DRB1∗0407.
Association of HLA subtype DRB1∗0407 in Colombian patients with actinic prurigo
Suárez A, Valbuena MC, Rey M, et al. Photodermatol Photoimmunol Photomed 2006; 22: 55–8.
These associations are not a feature of polymorphic light eruption. The absence of HLA-DR4 can help to rule out the diagnosis of AP, whereas the presence of HLA-DRB1∗0407 helps to rule in the diagnosis.
Actinic prurigo: clinical features and HLA associations in a Canadian Inuit population
Wiseman MC, Orr PH, MacDonald SM, et al. J Am Acad Dermatol 2001; 44: 952–6.
No statistically significant association of AP with HLA-DR4 (frequent in the studied population) or HLA-DRB1∗0407 was detected, and another HLA type (DRB1∗14) was found more commonly than expected, although it was only present in 19 of 37 AP subjects. The authors acknowledge the possibility that they were studying a different condition from AP in other populations.
Actinic prurigo in Singaporean Chinese: a positive association with HLA-DRB1∗03:01
Chen Q, Shen M, Heng YK, et al. Photochem Photobiol 2016; 92: 355–9.
In this population the strongest association was with HLA-DRB1∗03:01, although it should be noted that although a strong association was compared with controls, only six of these 14 Chinese Singaporean patients diagnosed with AP had this HLA allele.
These findings suggest we should be cautious in attempting to use HLA typing as a diagnostic test, especially in populations in which strong HLA associations have not been confirmed. The diagnosis should still be based on the characteristic constellation of clinical features.
Actinic prurigo of the lower lip – review of the literature and report of five cases
Mounsdon T, Kratochvil F, Auclair P, et al. Oral Surg Oral Med Oral Pathol 1988; 65: 327–32.
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