The definition afforded to Polymorphic Light Eruption (PLE) centres on skin eruption created by artificial UVR or natural sunlight, predominantly at temperate latitudes, that affects any subject following a sun exposure varying from hours to days, with the effects ongoing for several days or weeks following the termination of exposure. Overall, eruption tends to be symmetrical, and can be erythematous, itchy or skin-coloured, non-scarring and papular, although there are occasions when it may be present as plaque, bullous, vesicular, or an combination of such. It is very common for exposed skin to be affected, but not so often when the skin is covered. Furthermore, younger women are more likely to be affected and most commonly in the spring. PLE is a DTH (delayed-type hypersensitivity) reaction against endogenous cutaneous photoantigen recognised most commonly (1)
Ultraviolet radiation is the most common cause of PLE eruption and it is most common for the trigger to be early summer sunlight at temperate latitudes (1) ,while visible artificial sources radiation exposure such as sunbeds, rarely caused PLE (2, 3) . In addition, albeit to a lesser degree of reliability, broadband UVB (4) has also been recognised as valuable cause of PLE (5). When considering such ambiguities, however, a specific and clearly outlined action plan for PLE induction has been questionable especially when there is much variation from patient to patient, in addition to the fact that approximately 25% of all patients demonstrate isolated UVB sensitivity, whilst 25% show sensitivity to both UVA and UVB, whilst 50% are sensitive to UVA alone (6, 7) .
There is some indication that a genetic basis is apparent in PLE ,recognised as affecting the families of patients more commonly than the general population(8, 9) .with as much as 70% of the population recognised as carrying a susceptibility allele. Nonetheless, amongst genetically susceptible individuals, disease expression is influenced by environmental elements (9).
In temperate regions, PLE is recognised as most common, with as much as 10–20% of the population in these areas affected (8, 10-12) ,especially young women; tropical regions are recognised as having far lower prevalence (11, 13) . It is most common for PLE instances to occur in spring and summer as a direct result of exposure to the sun, with the initial attack quite commonly following lengthy periods of exposure; however, severity is seen to gradually diminish by the end of the summer and in the lead-up to autumn.
Eruption distribution in patients overall is characteristic; however, time and exposure intensity can affect this. It is common for the bridge of the nose to be affected, in addition to the cheeks, chin, upper chest, dorsa of the hands, dorsolateral aspects of the arms, the fronts and backs of the legs, and the dorsa of the feet. There are significant variations in lesional morphology and distribution between patients; overall : there are grouped, erythematous or skin-coloured, small or large papules; these may merge into irregularly surfaced or smooth plaques. It is also possible for swelling to occur, with small popular. PLE sparing the face, commonly affecting women when on holiday; across continental Europe, reference may be made to benign summer light eruption (14), with eruption on the light-exposed helices of boys’ ears, which is often vesicular and initially reported in springtime epidemics, commonly referred to as juvenile spring eruption (15-17) .In some rare instances, PLE may also go hand-in-hand with other symptoms, including chills, fever, headache, nausea, systematic malaise, and even erythema multiforme attacks(18,19) .
Diagnosis is made through the completion of a review of the patient’s history, clinical results, extractable nuclear antibody titres and negative circulating antinuclear factor, and normal blood, stool and urinary concentrations. On one hand, when there is ambiguity, lesional histology may give valuable diagnostic information, although it is not common for this to be diagnostic test. On the other hand, skin irradiation monochromator tests might be able to determine decreased minimal erythemal, when there is uncertainty,
Diagnosis of solar urticaria is made usually in line with its remarkably fast onset following exposure, usually within 5–10 minutes, and with consideration to various other symptoms, including different lesional morphology. Erythropoietic protoporphyria may be diagnosed in line with its painful nature, typical lack of rash and increased red blood cell protoporphyrin concentration, whilst light-exacerbated seborrhoeic and atopic eczema could be determined in line with their eczematous clinical and histological features and distributions. Lupus erythematosus might be seen to arise prior to, or at the same time as, PLE and may be recognised by its characteristic circulating and cutaneous immunological findings. Furthermore, erythema multiforme could be established by its clinical features, distinctive histology, and not infrequent link to a precipitating agent (20, 21).
The management of mild PLE may be achieved by limiting skin exposure to UVR, keeping the skin covered with suitable material, and making use of high-protection sunscreen (22) When patients are more seriously and frequently affected, prophylactic broad, narrowband UVB phototherapyor PUVAmay be selected as management methods (23, 24) .When an instance is recognised as a treatment-induced PLE flare, the decision to dispense oral steroids may be made .When PLE attacks are only occasion, however, or should there be the onset of a rash despite the application of the aforementioned measures, oral steroid courses—notably for a short period, with prednisolone 25–30 mg atthe earliest onset of itch, followed by doses every morning until clear—may be advisable, for only for a maximum of approximately 10 days in any three-month period (25) .Oral azathioprine and ciclosporin are also recognised as valuable in more extreme cases (26, 27)
- Actinic Prurigo
Actinic Prurigo (AP) is recognised as a rare condition caused by sunlight, with symptoms including severely itchy papular or nodular, commonly excoriated eruption of light-exposed skin, although in some instances, covered skin is affected. Summer is recognised as the most peaked time, with spring and autumn less common, and winter rare. Although AP can occur at any age, childhood onset is most common, with indefinite persistence a possibility, although many cases resolve during adolescence. It is believed that AP is the most persistent of PLE types, but is commonly clinically distinct.
UVR in AP is recognised as having a casual role as determined by its commonly more pronounced severity in summer, in addition to abnormal skin responses to monochromatic irradiation (28-30) ,with approximately 50% of these as a result of UVB alone, the same percentage to both UVA and UVB, with just a select few to UVA alone. Accordingly, it is apparent that AP is a persistent PLE variant and also may be viewed as a DTH response against endogenous cutaneous photoantigen.
It is common for AP to be witnessed across all ages, although childhood is when it is most prevalent and mostly amongst females. Although indefinite persistence is common and it may resolve itself during adolescence (31) . It is common for there to be a family history of AP or PLE with eruption likely to be seasonal (9) . Overall, the rash is seen to be pruritic, with early erythematous papules or nodules commonly becoming rapidly excoriated, crusted and scabbed, not infrequently with associated eczematization or lichenification. The sites most commonly affected are the distal limbs and the face, with forehead and the proximal limbs affected to a lesser degree, with the rash usually fading when examining those areas of the body usually covered with clothing. Nonetheless, severe cases may also demonstrate symptoms on the buttocks and the sacral area. Furthermore, hypo- or hyperpigmented healing lesions or flat white scars might also be seen on the limbs, with the face also showing minute, linear or pitted scars (32, 33).
Carefully examining medical history, with consideration to the most appropriate examination findings facilitates diagnosis, with attention directed towards normal circulating antinuclear factor and extractable nuclear antibody titres, and the concentrations of blood, urine and stool porphyrin. In some cases lacking clarity, it may be useful to consider early lesional histology. Immunofluorescence findings are negative. Should there be a continued lack of clarity, it might be useful to complete irradiation monochromator tests, which could go some way to determining light sensitivity in up to two-thirds of all patients. Atopic eczema and prurigo, especiallythat which is light-aggravated, can usually be determined through examining a patient’s history, appearance and distribution. A shorter period of time and commonly asymmetrical nature may help to determine insect bites, whilst scabies can be diagnosed through the presence of the mite. Furthermore, prurigo nodularis may be determined by its lack of seasonality, with adult onset most common, with lesions usually seen to be more widespread, while erythropoietic protoporphyria may be diagnosed by present of facial scarring, as well as through its elevated red blood cell protoporphyrin concentration.
Putting in place restrictions to sun exposure might facilitate recovery from mild AP, as well as the use of normal clothing cover and the use of high-protection sunscreen. Furthermore, should there be the presence of a rash, emollients and topical steroids may be prescribed. On the other hand, however, when patients not be overly responsive, occasional oral steroid courses may be advisable in dealing with attacks, with topical tacrolimus or pimecrolimus administered occasionally. When the condition is more persistent, however, oral ciclosporin may be advisable: this may achieve a good response (34).
- Hydroa Vacciniforme (HV)
HV may be defined as an uncommon acquired photodermatosis, with childhood onset most common, with the condition distinguished through crust, scar and vesicle formation after a period of sunlight exposure.
The condition’s origin has not yet been identified. It appears that exposure throughout spring and summer, especially in the case of exposure to UVA wavelengths, is most responsible (35, 36). During more recent times, a link between HV and EBV (Epstein–Barr Virus) has been suggested (36, 37)
Despite the fact that prevalence is unknown, HV is recognised as an uncommon, somewhat erratic condition, although on occasion is recognised as familial (38). It arises in both males and females (39) . During the first ten years of life, the condition usually becomes apparent; however, late-onset is also recognised as possible (40). Within a period of 12–24 hours following exposure to sunlight, either directly or through glass, papules and vesicles, notably haemorrhagic and pruritic, are seen to appear on an erythematous background. It is most common for the ears, nose, hands and cheeks to be affected . With the resolution of the lesions, a crusting phase is witnessed, with permanent scars then to follow, which can cause disfiguration to the affected areas(41) . In some children, acute episodes may go hand-in-hand with systemic malaise (42).
On occasion, there may be some degree of eye involvement; this may be seen through anterior uveitis, which may encompass corneal clouding and visual impairment(43) . In the majority of such instances, adulthood resolves the HV, with 9 years tending to be the average duration of the condition (39). In a select few instances, however, disease activity may be ongoing and continue on into middle age (44) .
The condition may be treated with photoprotection with the use of suitable clothing and also a broad-spectrum high-level sunscreen. Should the patient demonstrate non-responsiveness, it may be advisable to implement springtime prophylactic therapy with the use of broad-band UVB, narrow-band UVB or PUVA, all of which may provide positive outcomes(39, 45, 46)
- Solar Urticaria
Solar Urticaria (SU) may be recognised as primary (idiopathic) or secondary to porphyrias, phototoxic drugs and chemicals. More specifically, idiopathic SU may be defined as a rare wealing disorder caused by UVB, UVA and visible wavelengths. SU is a rare photodermatosis, and is regarded as being an immediate-type hypersensitive reaction, commonly to UVA (320-400nm) and visible (400–700nm), but less commonly to UVB (290–320nm) and rarely to infrared radiation.
SU is widely recognised as an allergic Type 1 hypersensitivity response , which may be resolved through the use of histamine [2,3] alongside other agents. Notably, from one patient to the next, there is variation in provocation wavelengths, and these may demonstrate change throughout the life of the disease ; this implies a series of photoallergens induced by UVB, UVA and visible light, either in combination or on their own. SU, when instigated by visible light, provides findings that could indicate the increased likelihood of a porphyria.When it is possible that secondary SU is apparent, a review of a drug history and the conduction of tests would be advisable so as to ensure porphyria is excluded.
Idiopathic SU prevalence and statistics are unknown. The condition is known to arise regardless of gender, although females tend to be more prone. It can arise at any age, although it is more common to occur during the ages of 20–30 years . Importantly, all races can be affected, although the distribution of prevalence is unknown. It is more common for the condition’s onset to make itself known within minutes of exposure, notably through the appearance of erythema, with other symptoms including itching and whealing, wherever sun exposure has been permitted. From one patient to another, there is variation in provoking wavelength sensitivity, with some individuals requiring only 2–3 minutes of light exposure, whilst others may require 60 minutes or even longer periods. Patients also might experience erythema, weal and flare when wearing thin light-coloured clothing that facilitates wavelength permeation. It is common for lesions to be at their most apparent for only a couple of hours, with fading then recognised, with an erythema then left that may be apparent for 24 hours or even longer periods, thus representing a delayed component. After the resolving of an episode, it may be that the skin is able to withstand subsequent provocation for a number of hours. When there is a significant and extensive reaction of the skin, other symptoms might also be observed, including bronchospasm, light-headedness, nausea and syncope . Idiopathic SU is known to resolve spontaneously in half of all cases, with 5 years generally tending to be the average period before resolution is witnessed . The severity of the condition might vary, with some periods not as problematic as others.
Wavelength dependency information is recognised as essential when seeking to manage the condition.Despite the fact that some patients are only mildly affected and therefore only need to ensure light-avoidance wherever possible and the use of a good sunscreen, others, in contrast, might need to take antihistamines early in the morning before being exposed to sunlight. It is stated that approximately one in every three individuals respond to non-sedative H1 blockade , with a further one-third seen to experience relief to a degree. Further benefit might be derived from the use of a H2 antagonist . It is interesting to note that antihistamine response  may be drug- and dose-dependent. Successful desensitization with photochemotherapy (PUVA) , UVA  and UVB (TL-01) [25,26] has been seen in some cases; however, the positive outcomes in this regard may be only temporary. Limited treatment to commonly photoexposed sites may be combined with antihistamines, and should be preceded by a minimal urticarial dose (MUD) determination.
When patients are very severely affected, however, such as when an individual is not responsive to more standardised treatments, it may be worth considering plasmapheresis, especially should a positive result be garnered when carrying out an intradermal test [27,28]; this may then be combined with PUVA . On the other hand, ciclosporin  or intravenous immunoglobulin  might be considered useful.
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