Chronic Actinic Dermatitis

 

EPIDEMIOLOGY

Chronic actinic dermatitis (CAD) has regularly been diagnosed in the United Kingdom, continental Europe, United States, Australia, New Zealand, Japan, and India, and patients from Africa have also been seen. The disorder therefore appears to be of worldwide incidence and to affect all skin types, although it is perhaps more common in temperate regions.

 

ETIOLOGY AND PATHOGENESIS

The likely pathogenesis of CAD has gradually been clarified, although it is not yet fully understood. Detailed studies of its clinical, histologic, and immunohistochemical features all show it precisely to resemble the DTH reaction of allergic contact dermatitis, even in its severe pseudolymphomatous form (formerly called actinic reticuloid), in which the clinical and histologic features are the same as those seen in long-standing allergic contact dermatitis. It is therefore highly probable that CAD is a similar reaction; however, given that it occurs after irradiation without any contact allergen in place, the reaction is presumably in this instance against photo-induced endogenous skin antigen(s).

Assessment of the action spectrum for CAD should theoretically help identify the postulated antigen, and this has been shown to resemble in shape that for sunburn in many patients. However, the eruption in CAD is eczema, although much lower exposure doses than required for erythema are often needed to evoke the response. Hence, the UVR absorber in such cases may be the same as that implicated in sunburn—namely, UVR-damaged DNA⁷³—but in CAD acting as an antigen. In other cases of CAD, however, the photoallergen must be different, because some patients react only to UVA and perhaps a very few others just to visible light.

In summary, CAD appears to be an allergic contact dermatitis-like reaction against UVR-altered DNA or a similar or associated molecule, or more rarely other molecules, perhaps as a result of enhanced immune reactivity due to concomitant airborne contact dermatitis or else reduced immunosuppressive capacity in photodamaged skin, or both, mainly in individuals with long-standing exposure to sunlight and airborne allergens.

 

CLINICAL FEATURES

 

History.

CAD may arise de novo in apparently normal skin or in the skin of patients with previous endogenous eczema, photoallergic or allergic contact dermatitis, perhaps occasionally oral drug photosensitivity, or rarely PMLE. Concurrent allergic contact sensitivity to frequently encountered, often airborne, substances such as plant allergens, fragrances, or sunscreens is also common. The condition usually affects middle-aged or elderly men, occurrence under 50 years of age being unusual except in patients with prior atopic eczema. The disorder is worse in summer and often also within minutes to hours of specific sun exposure, demonstrating a pruritic confluent erythematous eruption that occasionally settles over days with scaling if exposure ceases and the condition is mild. However, severely affected patients frequently do not recognize exacerbations with sun exposure, particularly if affected all year round.

 

Cutaneous Lesions.

 

The lesions in CAD may be patchy or confluent and are eczematous, whether chronic, subacute, or acute . In more severe cases, lichenification is common. More rarely, scattered or widespread erythematous, shiny, infiltrated pseudolymphomatous papules or plaques are present on a background of erythematous, eczematous, or normal skin. Habitually exposed areas are most often affected, commonly with sharp cutoff at lines of clothing, along with sparing particularly of the depths of skin creases, the upper eyelids, the finger webs, and the skin behind the earlobes. In severe disease,

eczema of the palms and soles is also possible; eyebrow, eyelash, and scalp hair may be stubby or lost from constant rubbing and scratching, and erythroderma, usually but not always accentuated on exposed sites, may rarely supervene. Variable, sometimes geographic, sparing of exposed areas of the face or elsewhere, as well as irregular hyperpigmentation and hypopigmentation, sometimes vitiligo-like, may also occasionally occur.

 

LABORATORY TESTS

 

Histology.

Histologic features include epidermal spongiosis, acanthosis, and sometimes hyperplasia, along with predominantly perivascular lymphocytic cellular infiltration confined to the upper dermis, with milder cases demonstrating just chronic eczema. Severe CAD, however, may histologically mimic cutaneous T-cell lymphoma (CTCL), on occasion being virtually indistinguishable, with epidermal Pautrierlike microabscesses and deep, dense epidermotropic mononuclear cell infiltration, sometimes with hyperchromatic convoluted nuclei and giant cells, but no marked increase in mitoses. T-cell receptor gene rearrangement studies should be undertaken if there is any suspicion of lymphoma.

 

Blood Tests.

 

Assessment of the circulating anti-nuclear and extractable nuclear antibody titers is advisable in all patients to exclude the unlikely possibility of subacute cutaneous or other form of lupus. In severe or erythrodermic CAD, there may be large numbers of circulating CD8⁺ Sézary cells without other suggestion of malignancy.^79,80 Human immunodeficiency virus status should be checked if there is any suspicion that this infection may be a predisposing factor.

 

Phototesting.

 

Phototesting is essential if available to confirm the diagnosis of CAD. Results are virtually always characterized by low erythemal thresholds and eczematous or pseudolymphomatous responses after irradiation with UVB, usually UVA, and rarely also the visible wavelengths. A very small number of patients react only to UVA,⁷⁴ and fewer still to only 600-nm visible light, in which case drug photosensitivity must be carefully excluded. Testing should preferably be on uninvolved skin of the back with no topical or systemic steroid therapy for at least the preceding few days to avoid false-negative results. Monochromatic and broad-spectrum sources both induce abnormal responses, with the former determining the action spectrum for disease induction and the latter tending to demonstrate acute eczema.

Patch and Photopatch Testing.

Patch and photopatch testing is also essential in suspected CAD, because contact sensitivity to airborne allergens such as Compositae oleoresins, phosphorus sesquisulfide, and colophony alone may closely resemble CAD or else co-exist. In addition, occasional secondary contact or photocontact sensitivity to sunscreens or other topical therapies may further complicate the clinical picture.

 

DIFFERENTIAL DIAGNOSIS

COMPLICATIONS

Any relationship to lymphoma seems likely to be coincidental, particularly because the results of T-cell receptor, immunoglobulin gene rearrangement, and other similar studies are negative in CAD. In addition, CAD gradually resolves in many patients, there is no higher incidence of malignancy in CAD patients than expected, and life expectancy of CAD patients is normal. However, it has been suggested that CTCL itself may very rarely present with severe CAD-like photosensitivity, and careful investigation to exclude CTCL is necessary if that disease is suspected.

Box 90-4 Differential Diagnosis of Chronic Actinic Dermatitis

·         Photo-exacerbated atopic or seborrheic eczema

·         Drug or chemical photosensitivity

·         Cutaneous T-cell lymphoma

·         Eczematized actinic prurigo

 

PROGNOSIS AND CLINICAL COURSE

 

Once established, CAD usually persists for years before not infrequent, very gradual resolution.

 

TREATMENT

 

The treatment of CAD is often difficult and not fully effective. Rigorous avoidance of UVR and exacerbating contact allergens is essential, along with the regular application of high protection-factor broad-spectrum topical sunscreens of low irritancy and allergenic potential. Strong topical steroids such as clobetasol propionate are also often needed and frequently produce marked symptomatic relief without adverse effects, even after long-term use, if confined to affected skin; occasional oral steroid use is often helpful too for disease flares. In more resistant disease, the topical calcineurin inhibitors tacrolimus and pimecrolimus can sometimes produce good results if tolerated.^86,87 For refractory CAD, however, oral immunosuppressive therapy is almost always necessary and generally helpful if tolerated. Azathioprine 1.5 to 2.5 mg/kg/day often produces remission in months, after which it may be reduced in dosage, or perhaps discontinued in the winter. Cyclosporine 3.5 to 5.0 mg/kg/day is usually rapidly effective⁸⁹ but is more likely to produce adverse effects, which sometimes necessitate withdrawal. Mycophenolate mofetil is less often useful, whereas thioguanine has been used with good effect by one of the authors. Finally, long-term low-dose phototherapy with PUVA, usually several times weekly initially followed by maintenance exposures every 3 weeks or so, may be helpful,⁹⁰ generally accompanied initially by oral and topical steroid therapy to avoid disease flares .

 

PREVENTION

 

The risk of CAD development can probably be reduced by the moderation of outdoor pursuits, particularly those associated with plant allergen exposure such as gardening, especially for individuals who already have a tendency to eczematous eruptions in exposed areas.