Last updated: 6 February 2010.
Introduction
Actinic PrurigoActinic Prurigo is a chronic, pruritic skin disease, where symptoms present hours after exposure to UV light. Click here for more information. (AP) is a rare, itchy and chronic skin condition caused by an abnormal reaction to sunlight. Skin lesions can appear hours to days after sun exposure and rarely, non-exposed skin can be affected. AP is also known as Hutchinson prurigo.
Incidence
Actinic PrurigoActinic Prurigo is a chronic, pruritic skin disease, where symptoms present hours after exposure to UV light. Click here for more information. usually begins in childhood and generally persists into adulthood. AP can occur in all races, but is usually seen in Latin Americans and the indigenous populations of the Americas. The prevalence of AP in the general population is not known, but is thought to be less than 5% in the above-mentioned populations. In Europe and the Asia-Pacific, where a pathogenetically similar but clinically distinct disease known as polymorphic light eruptionAlso known as PLE, PME or PMLE, Polymorphic Light Eruption is the most common skin disorder characterized by photosensitivity and, after sunburn, is the most common sun-related problem seen by doctors. Click here for more information. (PLE) is more common, rare cases of AP have been reported.
Causes
Sun-exposure, i.e. exposure to ultraviolet A and B radiation, is the predominant cause of actinic prurigoActinic Prurigo is a chronic, pruritic skin disease, where symptoms present hours after exposure to UV light. Click here for more information.. The reason for the abnormal response to sun exposure is not fully understood. An immune-mediated response to ultraviolet radiationUltaviolet (UV) radiation is emitted by the sun, and is a region in the electromagnetic spectrum between 400-200nm, that can be broken down into three categories: UVA which is between 400-320nm, UVB which is between 320-280nm, and UVC between 280-200nm. Click here for more information. in the background of genetic predisposition is thought to explain the symptoms associated with AP.
Symptoms
The symptoms of actinic prurigoActinic Prurigo is a chronic, pruritic skin disease, where symptoms present hours after exposure to UV light. Click here for more information. include:
- Extremely itchy skin rash;
- Red and inflamed bumps (papules);
- Thickened patches (plaques); and/or
- Lumps (nodules)
In addition to the symptoms listed above, skin ulcerations, crusting and scaling can occur. These symptoms resemble atopic dermatitisAtopic Dermatitis (atopic eczema) is a chronic, highly pruritic, eczematous skin disease characterized by extreme hypersensitivity to allergens. Click here for more information., but sun-exposed areas such as the nose are more commonly affected in AP. The conjunctivae and the lips are also often involved in individuals with AP.
AP is diagnosed based on clinical assessment. As a skin disease that does not involve internal organs, no blood tests are available to diagnose AP. Nevertheless, blood tests may be performed to rule out systemic diseases with involvement of the skin. Histological studies may be helpful. Phototesting may help with the diagnosis, but is non-specific and does not rule out other photosensitive disorders.
Treatments
Actinic PrurigoActinic Prurigo is a chronic, pruritic skin disease, where symptoms present hours after exposure to UV light. Click here for more information. is seldom cured. The disease may resolve before adulthood in some individuals. In others, however, it is persistent and seasonal outbreaks during summer and spring may occur. Rarely, AP may arise in adulthood and persist throughout life. Treatment is aimed at prevention and controlling symptoms. Avoiding UV exposure and appropriate sun protection measures may be beneficial.
Prophylactic phototherapy may be helpful in some cases. Other treatment options include:
- Emollients to relieve itching;
- Topical steroids;
- Topical calcineurin inhibitors, such as tacrolimus or pimecrolimus;
- Thalidomine (can cause birth defects in women of childbearing age); or
- Oral immunosupprssants, such as azathioprine or cyclosporine.
Introduction
Actinic Prurigo (AP) is a chronic, idiopathic dermatosis, which is characterised by abnormal cutaneous responses to ultraviolet radiation (i.e. photosensitivity). AP is thought to be mediated by an abnormal immune response in the background of genetic predisposition. AP is a rare condition and is usually seen in certain populations of the Americas. Skin lesions can appear hours to days after sun exposure and rarely, non-exposed skin can be affected. AP is also known as Hutchinson prurigo. Although AP is not associated with mortality, it can cause significant morbidity in afflicted individuals.
Epidemiology and prevalence
Actinic Prurigo can affect the skin of all races, although it is more commonly observed in Latin-American Mestizo and Native American populations. Sporadic cases have been reported in the United Kingdom, the United States, Europe, Australia and Japan. AP usually begins in adulthood. In some individuals, it may resolve before adulthood. In others, however, it is chronic and tends to recur persistently. Rarely, the disease may arise in adults and the clinical course in these cases is usually chronic.
The prevalence of AP in the general population is not known. It has been estimated that less than 5% of all referrals to photodermatology clinics have AP. In Europe and the Asia-Pacific, the pathogenetically similar, but clinically distinct disease known as polymorphic light eruption (PLE) is more common than AP.
AP tends to occur equally in both the sexes in children and adolescents. In adults, however, females are twice as frequently affected as males. A positive family history of AP or PLE is present in one-fifth of individuals with AP
Typically, AP first appears in the sunnier months and patients often report exacerbations in symptoms during summer and spring. Rarely, however, the symptoms are worse during winter and autumn, and immunological tolerance during summer is thought to be responsible for this phenomenon.
Clinical features
The skin lesions characteristic of actinic prurigo are very pruritic papules or nodules, sometimes associated with eczematisation, lichenification and crusting. Large plaques can occasionally be seen. Although areas exposed to the sun, such as the cheeks, nose and hands, are more commonly affected, non-exposed areas can rarely occur in severe AP. Pseudoalopecia of the eyebrows can occur if the face is constantly scratched. In severe cases, permanent mild scarring and hypopigmented lesions may develop.
In about 65% of the patients affected with AP, the lips are affected. Inflammation of the lip (cheilitis) and pruritis are commonly observed. Other features such as oedema, crusting, ulceration and scales may be present. Interestingly, in 10% of the patients with AP, the lips are the only sites that are affected.
The conjunctivae of the eyes are affected in about 45% of patients with AP. Hyperaemia, brown pigmentation, photophobia, epiphora (excess production of tears), and formation of pseudopterygium (where the conjunctiva adheres to the cornea) are potential symptoms associated with the involvement of conjunctivae.
Diagnosis of AP is based on clinical assessment, and the pathological study of the mucosae of the lips, conjunctivae, or the skin. The minimal erythema dose, the minimum dose of narrow-band ultraviolet (UVB) radiation that is required to produce redness 24 hours after exposure, is reduced in patients with AP. It should be noted that a negative cutaneous phototesting does not exclude the diagnosis of AP. Also, a positive result does not distinguish between AP and other photodermatoses, such as Polymorphic Light Eruption. The presence of HLA type DRB1*0401, or DRB1*0407 in genetic testing is suggestive of AP.
Histologically, mild acanthosis, exocytosis, and spongiosis of the epidermis are observed. Lymphocyte infiltration and lymphoid follicles may be present. Eosinophils are often present. With the conjunctival histology, the epithelium appears thinned and atrophied. The basal cells are vacuolised with lymphocytic infiltration in the sub-mucosal follicles. Eosinophils are conjunctival pigmentation are common findings. The presence of lymphoid follicles in the mucosal and conjunctival laminae is the most characteristic pathological finding in AP.
Other laboratory tests are used to rule out other systemic diseases with a photosensitivity component, rather than to diagnose AP. The presence of anti-nuclear antibodies and extractable nuclear antibodies should be undertaken to rule out lupus. The highly contagious Scabies should always be ruled out prior to diagnosing AP. When the skin on the nose is not affected, the condition is more likely to be photosensitive atopic dermatitis than AP. Polymorphic Light Eruption and Prurigo Nodularis are other morphologically similar diseases that should be excluded during the diagnosis of AP.
Aetiology and pathogenesis
Actinic Prurigo arises due to abnormal cutaneous responses to ultraviolet radiation (photosensitivity). The causes of AP are not known. AP is believed to be delayed-type hypersensitivity reaction to antigens exposed or changed following exposure of the skin to ultraviolet radiation. The exact nature of these antigens is not known. It is believed that genetic predilection may play a role in the pathogenesis of AP, with up to 90% of patients with AP showing various human leukocyte antigen (HLA) variants. In particular, HLA type DRB1*0401 and HLA type DRB1*0407 have been associated with AP.
Skin lesions in AP have been shown to be infiltrated by CD4+ T cells. An abnormal immune sensitization occurs against epidermal antigens in AP. AP can be considered as an autoimmune disease, because lymphocyte activation occurs in response to patient’s own ultraviolet-irradiated keratinocytes.
Expression of cell adhesion and activation molecules has been shown to be increased in AP. This suggests that lymphocytes in skin lesions of AP are, therefore, activated and may play a role in the damage observed in this condition. An increased adhesiveness of lymphocytes, as a result of increased expression of adhesion molecules, enables them to migrate through the endothelium and extracellular matrix. Similarly, the activation molecules can act on their respective receptors to induce lymphocyte proliferation and activation. Ultraviolet radiation is thought to activate adhesion molecules, such as ICAM-1, via activated lymphocyte infiltrates in keratinocytes, leading to inflammation that is observed in AP.
Langerhans cells (LC) are believed to play a role in the pathogenesis of AP. LC are antigen presenting cells that are involved in the inducti0n of cell-mediated immune responses to antigens located in the skin. LCs in patients with AP show a reduced susceptibility to ultraviolet radiation. UV-resistant LCs in patients with AP activate immune responses via putative antigens. Because of the presence of UV-resistant LCs, the putative antigens may be delivered to lymphocytes in large amounts or in a chronic fashion, leading to inflammation seen in AP. Thus, a combination of altered expression of adhesion molecules and UV-resistant LCs may be involved in the pathogenesis of AP. Further studies are required to elucidate the identity of these putative antigens and to gain a better understanding of the disease process.
Prevention
Actinic Prurigo is an idiopathic disease – i.e. the precise causes of AP are unknown. As sun exposure is the primary trigger of the disease, prudent steps must be taken to reduce or avoid exposure to the sun. The use of sunglasses, wearing appropriate clothing, and the appropriate use of sunscreen may be beneficial. In case of excoriations, sunscreen should be used cautiously. Patients should be taught about the appropriate application of sunscreens. Patients should also be made aware that even minor exposure to ultraviolet radiation may result in outbreaks or exacerbations of symptoms. Annual prophylactic phototherapy may be of benefit in some patients.
Treatment
Preventative measures are important in managing actinic prurigo. The use of topical corticosteroids may be effective in managing mild disease, via their anti-inflammatory effects. Oral steroids may be necessary in more severe disease. Hypersensitivity and infections are possible side-effects of steroid use. Anti-malarial drugs, such as chloroquine, may be effective in some cases. These drugs have anti-inflammatory and photoprotective effects. Also, topical calcineurin inhibitors, such as tacrolimus, may be used to treat relatively mild AP.
Oral thalidomide, an immune suppressant, is usually effective in treating more resistant AP in all age groups. Adverse effects include drowsiness, headache and weight gain. Nerve conduction studies should be performed regularly to assess for peripheral neuropathy, another side-effect of thalidomine treatment. Thalidomide is teratogenic and pregnancy must be avoided. Other immune suppressants include cyclosporine and azathioprine, which may be useful if other treatments are ineffective.
Prophylactic phototherapy with UVB or PVB in spring, when the symptoms usually worsen, may be effective in some patients.
Prognosis
Actinic Prurigo usually arises in childhood, and persists into adulthood. In some individuals, AP can improve or resolve before adulthood. Rarely, it may arise in adulthood, and persist chronically. Although not a fatal disease, AP can lead to significant morbidity, with exacerbations during the sunnier months. Secondary infections and impetigo are potential complications. Irritant contact dermatitis can manifest with inappropriate use of sunscreens.
