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IDIOPATHIC PHOTODERMATOSES

Polymorphic light eruption

Etiology and pathogenesis

Polymorphic light eruption (PLE) is the commonest of the idiopathic photodermatoses. The true incidence is uncertain, as minor versions are often misinterpreted as sunburn or as prickly heat. In most series, it is commonest in women, and may occur in up to 30% of young women using tanning beds. It is familial in about 10% of cases. The onset is typically in the second decade, but earlier in 25%. About 10% of young women with this disorder may have a low-titer positive antinuclear antibody (ANA), but long-term follow-up does not suggest a progression to lupus erythematosus.

Clinical features

The eruption has mixed features, but generally follows a reproducible pattern in any individual. Some patients have predominantly papules (Fig.17.28), vesicles, urticated plaques, eczematous areas, or (less commonly) erythema multiforme-like lesions. Solar purpura may be a variant of PLE. Onset is usually from a few hours to a few days after exposure (typically 6–12h), and the eruption predominantly affects exposed sites; it fades after a few days without further exposure.

Figure 17.28Polymorphic light eruption on the legs. The pattern of eruption may be of urticarial pattern (as in this case), eczematous, or a mixture of the two.

    In most patients, the disorder is seasonal, with springtime predominance. The eruption typically appears during the first sunny days of the year and improves as the summer progresses. This process, known as ‘hardening', may involve increased UVB-induced tanning and thickening of the stratum corneum. Provocation may be by UVB, UVA, or both. This may be a reason why the condition in some individuals improves as the summer progresses, but in some (usually those more severely affected) continues to deteriorate. Patients who have significant UVB provocation are likely to have more episodes of skin eruption in later summer.

    The histologic features of PLE are a dense perivascular lymphocytic infiltrate in the upper and mid-dermis, and upper dermal edema. The edema may be prominent in the erythema multiforme-like pattern. There may be extravasation of erythrocytes. Mild vascular deposition of complement C3 has been reported in some patients. Lesions produced by provocation testing have this same histology, and biopsy of provoked lesions may be necessary in some individuals. Jessner lymphocytic infiltrate has similar histology, but edema is rarely marked. Lupus erythematosus may also have a similar appearance, but usually there is less perivascular infiltrate, and the abnormalities are predominantly at the dermo– epidermal junction; these include a lymphocytic infiltrate, basal epidermal liquefaction, thickened basement membrane, and deposition of complement C3 and immunoglobulin IgG, IgA, or IgM.

    Other tests that may be useful include serologic tests for lupus erythematosus, especially ANA and anti-SSA (anti-Ro). Although ANA may be positive in PLE, this is of low titer and occurs in only about 10% of patients. By contrast, about 90% of patients who have systemic lupus erythematosus have positive ANA, and most who have subacute cutaneous lupus erythematosus have positive anti-SSA.

Differential diagnosis

Polymorphic light eruption is virtually always a clinical diagnosis, but investigations may be required to distinguish it from other photodermatoses; from some non-photosensitive disorders; and (of greatest importance and difficulty) from photoaggravated disorders, especially lupus erythematosus (Table 17.5). Provocation tests can be useful, as can additional phototesting or photopatch testing if other photodermatoses are suspected.

    A particular difficulty for the physician is proving the diagnosis in retrospect in a patient who developed rash after their first day on holiday. Patients generally blame such rashes on heat (causing ‘prickly heat' or ‘heat rash', more accurately termed miliaria rubra) rather than blaming light; it is likely that PLE is underestimated. Both eruptions are likely to respond to avoidance of sun, as this usually parallels avoidance of heat. If the eruption affects covered sites mainly, then the diagnosis of miliaria may be confirmed, but often there are few covered sites to judge this. Another possible diagnosis in this situation is sunscreen allergy, but this usually becomes apparent with repeated exposure.

Treatment

This comprises topical corticosteroids, oral antihistamines, sunscreens, and sun avoidance. Low-dose PUVA or narrow-band UVB in early spring may produce hardening. Azathioprine is used for severe disease.

Juvenile spring eruption

Etiology and pathogenesis

This eruption may be a variant of PLE, but is clinically distinct.

Clinical features

The lesions consist of tiny blisters on the rim of the ears, typically in boys aged between 5 and 14 years (Fig. 17.29). They cause itch or pain, but are transient and usually last about 2 weeks. This is typically a disorder of early spring, but may occur throughout the summer and may recur on an annual basis throughout childhood. It typically starts 1–2h after exposure to intense sunlight, but phototests are normal and provocation tests are negative.

Figure 17.29 Juvenile spring eruption at the typical site on the helix of a young boy.

Differential diagnosis

Juvenile spring eruption is a clinical diagnosis, but some children are erroneously thought to have prolonged sunburn, herpes simplex, impetigo, porphyria or pseudoporphyria (usually due to naproxen in this age group), or dermatitis.

Treatment

Topical corticosteroids may be used. The important aspect is a broad-spectrum sunscreen to prevent the eruption, but benefit is variable. Physical barriers are most effective.

Solar urticaria

Etiology and pathogenesis

This is an idiopathic non-familial condition. Like other urticarias, it involves degranulation of mast cells to release histamine and other inflammatory mediators. It appears to involve IgE, but the involvement of other photoactive molecules is less clear. Passive transfer has been demonstrated, as the serum from some affected individuals causes the reaction when injected into non-photosensitive recipients.

    Most patients have sensitivity in the UVA range, but some also have sensitivity in the visible range, and a few in the UVB range. Some react only to visible light.

Clinical features

Lesions have the typical morphology of urticaria (Fig. 17.30). They occur on exposed sites (some may occur due to transmission of light through thin clothing). Onset is within minutes of exposure to light, and lesions last minutes to a few hours. As can be anticipated from the spectrum to which patients are sensitive, window glass rarely provides photoprotection. Artificial light sources, notably fluorescent lamps, are occasionally sufficient to provoke lesions. The condition is typically troublesome and often symptomatic throughout the year, significantly limiting normal activities. However, it may remit spontaneously after a few years in some patients.

Figure 17.30 Solar urticaria, occurring as a confluent sheet on the exposed V of the neck.

Differential diagnosis

The disorder is so characteristic in its onset within a minute or so of sunlight exposure that it is difficult for it to be mistaken for anything else. It may occasionally be confused with PLE if an accurate history of timing of onset is not obtained. It may also be confused with other urticarias in which symptoms may be restricted to outdoor activities, such as cholinergic urticaria (due to heat or exercise, which provoke sweating), exercise-induced urticaria, food-dependent exercise-induced urticaria, and heat urticaria (temperature-dependent rather than sunlight-provoked). Provocation tests are positive, usually to UVA (Fig.17.31). In young children, especially if the urticaria is not apparent for examination, it may be necessary to exclude erythropoietic protoporphyria.

Figure 17.31 Solar urticaria. This was provoked within 1 min of diagnostic phototesting, at all the doses administered.

Treatment

Avoidance and sunscreens are important. Physical methods to block UVR, such as special films applied to house and car window glass, may be necessary. Sunscreens may be useful, but most commercial preparations have a relatively poor UVA-blocking effect (up to about eightfold protection) and block very little visible light.

    Systemic antihistamines may produce an up to about 10-fold reduction in wheals and itch.

    Therapeutic UVB may produce useful tanning, epidermal thickening, and tolerance in individuals with UVA or visible light provocation, but will provoke urticaria in the 25 – 50% of patients whose sensitivity extends into the UVB range. Those patients who respond to UVB usually need maintenance treatments every fewdays (even daily) to achieve ongoing benefit. PUVA may also be useful, and can produce prolonged benefit. It may have immunologic effects in addition to tanning and skin thickening, but is often difficult to administer in patients with a high degree of UVA provocation.

    Immunosuppressive agents such as ciclosporin have been used with benefit, but in the author's experience have not proved helpful.

Hydroa vacciniforme

Etiology and pathogenesis

The etiology of this rare sporadic condition is uncertain. It is a clinically characteristic eruption in which histology shows epidermal degeneration, perivascular inflammation, vascular thrombosis, and necrosis. It is most common in boys, and is a recurrent problem in the summer months, but usually resolves in adolescence.

Clinical features

There is a papular and vesicular eruption of discrete lesions, which are predominantly at photoexposed sites on the face and hands or forearms (Figs 17.32 and 17.33). Milder cases heal with little residue (hydroa estivale), but the typical pattern is necrosis of the lesions with a varioliform appearance and scarring.

Figure 17.32 Hydroa vacciniforme. The close-up morphology is of non-specific papules, vesicles, and scabbed lesions, but with localization to photoexposed skin, as shown here on the arms.

Figure 17.33 Hydroa vacciniforme. Lesions on the cheek of the patient shown in Figure 17.32.

Differential diagnosis

The differential diagnosis includes herpes simplex, varicella, impetigo, erythropoietic protoporphyria, PLE, lupus erythematosus, and actinic prurigo. Investigations include phototests and provocation tests (which are sometimes positive with UVA), porphyrins, ANA, and anti-SSA.

Treatment

Sunscreens are of limited benefit. Antimalarials (discussed in the treatment of lupus erythematosus, see Ch.13) and b -carotene may be helpful.

Actinic prurigo

Etiology and pathogenesis

This disorder is rare in Europe , but has a strong familial tendency in native North and South American peoples. It is most common in girls. The histologic features are those of eczema (Ch. 6).

Clinical features

Initially, papules and vesicles develop in sun-exposed areas (Fig.17.34). It is most apparent in the summer, but often fails to clear completely in winter months, and generally progresses to a more eczematous morphology with plaques, lichenification, and crusting. It may clear in some patients in their late teens, but some cases are chronic.

Figure 17.34 Actinic prurigo. This disorder appears eczematous but occurs at exposed sites, typically in girls.

Differential diagnosis

This includes other photodermatoses, especially PLE and hydroa vacciniforme, and dermatitis of other causes, especially photoaggravated atopic disease. Phototests may be abnormal, and patch tests may be required to exclude contact dermatitis.

Treatment

This condition is generally refractory to treatment. Sunscreens are of limited benefit. Treatments for dermatitis (see Ch.6) are used, and severe cases may require immunosuppressive medication.

Chronic actinic dermatitis (photosensitivity dermatitis, actinic reticuloid)

Etiology and pathogenesis

This is a spectrum of disease that may progress from a chronic eczematous pattern of photosensitivity to a more infiltrated skin eruption (termed actinic reticuloid), which is difficult to distinguish histologically from mycosis fungoides. Some patients are those who have previously been diagnosed as having a photoallergy (see later) that has not resolved (also known as ‘persistent light reactors').

    In addition to abnormal phototest sensitivity (which usually spans UVB, UVA, and visible light), patients often have multiple contact allergies. Some of these appear logical (e.g. reactions to oleoresins of the Compositae plant family, fragrances, or lichens, which may all cause an airborne contact allergy), but others are less easy to explain (e.g. high frequency of reactions to chromate and rubber). There is also a high frequency of reactions to sunscreens, which may reflect many years of using these chemicals. The precise mechanism of chronic actinic dermatitis remains uncertain, and it is not known why some patients progress to develop a more lymphomatous pattern.

    The disorder typically occurs in the elderly, and there is a strong male predominance.

Clinical features

A diffuse eruption with eczematous morphology and severe itch initially affects the photoexposed areas of the body, but gradually spreads to covered sites (Figs 17.35 and 17.36). Some patients develop increasingly lichenified and indurated skin, which may produce a leonine facies and may have histologic features strongly suggestive of lymphoma. The problem is initially most apparent in summer, but the duration of symptoms gradually extends into winter months, and eventually the condition becomes perennial. Minor sunlight exposure, light through glass, and even fluorescent lamps may provoke symptoms.

Figure 17.35 Chronic actinic dermatitis. This is typically seen in elderly men. The close-up morphology is that of chronic dermatitis.

Figure 17.36 Chronic actinic dermatitis. (Same patient as in Fig. 17.35.)

Differential diagnosis

This includes drug-induced photosensitivity, photosensitivity due to external agents, eczemas (especially airborne contact dermatitis and late-onset atopy), drug eruptions, and (in its earlier stages) other photosensitivity disorders such as PLE. Patch tests, phototests, and photopatch tests are all indicated. Tests to plant extracts may be necessary, although a commercially available Compositae extract has simplified this test procedure; in Europe , this is a routine component of the Extended European Standard Battery of patch test agents.

Treatment

Patients who have positive contact reactions need to avoid the relevant agents. In particular, those who react to Compositae need to be warned about plants that may cause reactions, which vary in different parts of the world. This family includes chrysanthemum, dahlia, sunflower, cornflower, lettuce, chicory, feverfew, ragweed, and some other weeds; they may cross-react with colophony (a resin).

    Interventions include use of broad-spectrum sunscreens and physical protection from sunlight. UV-blocking museum film may be needed on house and vehicle windows. However, in some patients, the photosensitivity includes visible light, which is poorly blocked by sunscreens or window films.

    Topical and systemic corticosteroids may be helpful. Some patients respond to PUVA photochemotherapy. Azathioprine often gives good control, while other immunosuppressive agents such as ciclosporin have been used more recently.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.