Dermatitis artefacta is a self-inflicted dermatosis occurring in malingerers, the mentally handicapped, and in association with various psychiatric disturbances, particularly personality disorders.^{11. and 12.} The definition is sometimes extended to include factitious lesions resulting from child abuse.^{13. and 14.} Two reviews of the cutaneous manifestations of child abuse have recently been published.^{15. and 16.} Abuse by burning comprises approximately 6–20% of all child abuse cases.^{16. and 17.} Ecchymoses and bruising are further signs suspicious for abuse. ¹⁶

Dermatitis artefacta may take many different forms, depending on the injurious agent used.^{11.18.19.20. and 21.} Crusted erosions, ulcers, keloids, scars, psoriasis-like lesions, chemical and thermal burns, hair cutting and shaving are among the many lesions encountered.^{22.23.24.25.26.27.28.29. and 30.} Rarely it may masquerade as pyoderma gangrenosum. ³¹ In younger persons more than 50% of the lesions are on the head and neck.^{24. and 26.} Bullous lesions on the lower legs were reported in an adolescent, but the mechanism of their production was never elucidated. ³² The distribution and shape of these various lesions may be bizarre. Usually there are lesions in different stages of evolution. Deep abscesses, cellulitis, lipogranulomas, and other granulomatous lesions may result from the injection of various substances. ³³

It has been proposed that some ulcerations in patients with reflex sympathetic dystrophy may be of factitial origin. ³⁴

The terms dermatitis neglecta, ‘terra firma-forme’ dermatosis, and keratoderma simplex³⁵ have been used for acquired, asymptomatic plaques, often on the neck, resembling a pigmented lesion, a verrucous nevus, or acanthosis nigricans. They rub off with alcohol (see p. 299). ³⁶

Decubitus ulcers (bedsores) are a worldwide healthcare problem affecting tens of thousands of patients. ⁴⁰ They usually develop over pressure areas such as the sacrum, the greater trochanter, and the heels, usually in individuals confined to bed for long periods.^{41.42.43. and 44.} Prolonged pressure is thought to compromise the vascular supply of the affected areas, although the pathogenic steps leading to ulceration have not been investigated in detail.^{45. and 46.} Several clinical stages have been identified. There is a preceding erythematous stage (blanching and non-blanching) and a late stage in which a black eschar forms. ⁴⁷

Uncommonly, a cutaneous metastasis may mimic a decubitus ulcer. ⁴⁸

Pressure ulcers are difficult to treat, so prevention is an important strategy. The main treatment principles include reduction of pressure, friction and shear forces, local wound care, surgical debridement of necrotic tissue, and management of any secondary infection. ⁴⁹ A recent randomized trial found that traditional resin salve is significantly more effective in the treatment of severe pressure ulcers than cellulose polymer gauzes. ⁴⁹

Friction blisters are produced at sites where the epidermis is thick and firmly attached to the underlying dermis, such as the palms, soles, heels, and back of the fingers.52. ^{and 53.} A common site is the heel, where blisters are caused by ill-fitting footwear. ⁵⁴ Friction blisters are an uncommon manifestation of dermatitis artefacta. ⁵² If the trauma is prolonged and severe or the skin is thin, erosions will occur. Recovery is rapid and complete within a few days. ⁵⁵

‘Black heel’, which is usually bilateral and roughly symmetrical, consists of a painless, petechial eruption on the heels.^{54.60.61. and 62.} There is speckled, brownish-black pigmentation that may be mistaken for a plantar wart or even a melanoma. ⁶³ It should not be forgotten that melanoma can occur on the heel. ⁶⁴

Calcaneal petechiae appear to be traumatic in origin. Their formation probably follows a pinching force imparted by shoes at the time of sudden stopping, such as occurs in the course of basketball, tennis, and other sports.^{63. and 65.}

Lesions comparable in appearance, pathogenesis, and pathology occur in other situations.^{66. and 67.} They include jogger’s toenail, ⁶⁸ weeder’s thumb, ⁶⁹ and playstation thumb. ⁷⁰ They may follow the wearing of new shoes, or the pricking of a blister with a needle. ⁷¹ The term post-traumatic punctate hemorrhage has been proposed as a unifying term. ⁶⁶ Subungual blood may also be the presenting sign of an underlying tumor of the nail bed. ⁷² There are many causes of splinter hemorrhages of the nails. Trauma is the most common cause, but systemic illnesses, including cardiovascular, renal, and pulmonary diseases, are other etiological agents. Idiopathic cases also occur. ⁷³

Subungual hemorrhage produced by acitretin has also been reported. ⁷⁴

There is a common response to the different types of radiation that affect the skin, although the severity of the changes varies with the total dose, its fractionation, and the depth of penetration of the radiation.^{84.85. and 86.} The use of megavoltage therapy for deep tumors has resulted in some sparing of the skin, although fibrosis in the deep subcutaneous tissues may result.^{86. and 87.}

The advent of coronary angioplasties and stenting has resulted in several cases of radiation dermatitis as a consequence of excessive radiation, usually associated with a prolonged fluoroscopy-guided procedure. Lesions are usually on the upper back.^{88.89. and 90.} Presentations include a vascular lesion, a morphea-like lesion, skin necrosis, or an unexplained ulcer.^{89. and 91.} As already mentioned (see above) radiofrequency energy used in various cardiac ablation techniques can also produce localized radiodermatitis.

There is a well-defined progression of changes following irradiation of the skin. ⁸⁶ These are usually divided into early changes (acute radiodermatitis) and chronic changes (chronic radiodermatitis) arising many months or years after the initial exposure.^{92. and 93.} An intermediate (subacute) stage is also recognized. The complications of ionizing radiation have recently been reviewed. ⁹⁴

Thermal burns are an important cause of morbidity and mortality. In children, most burns are scalds from hot liquids, while in adults accidents with flammable liquids are more common.123.^{124.125. and 126.} Burns are sometimes a manifestation of child abuse. ¹²⁷ Acute lesions have traditionally been classified into first-, second-, and third-degree burns according to the extent of the damage. ¹²⁸ However, some surgeons categorize burns into superficial and deep types. Unfortunately, even this simple classification is difficult to apply on the basis of physical findings alone. ¹²⁹ A common but neglected phenomenon is the occurrence of blisters weeks to months following a burn, after initial successful healing of partial-thickness wounds. This ‘delayed postburn blister’ may occur for up to 12 months or more after injury. ¹³⁰ Its mechanism is unknown but it may be due to shearing forces in an area with reduced numbers of anchoring fibrils. ¹³⁰

Secondary infections, usually due to Gram-negative bacteria, are an important complication in the acute stage. Alopecia may follow a deep burn to the scalp. ¹³¹ A late complication, occurring 20–40 years later, is the development of a squamous cell carcinoma.^{132. and 133.} These tumors have a higher risk of metastasis than the usual squamous cell carcinomas of the skin. ¹³⁴ Basal cell carcinomas and, rarely, malignant fibrous histiocytomas or malignant melanomas may likewise develop many years after the injury.^{135.136.137. and 138.} Dystrophic xanthomatosis is another rare complication (see p. 962).

In the United States, the overall incidence of all burns is approximately 4/1000 per year, but only 3% occur as a result of electrical injury. ¹⁴¹ Electrical burns may be of variable severity, depending on the nature of the current, the voltage, and the extent of contact with the skin. They resemble third-degree thermal burns although in severe electrical burns there is deep vascular damage leading to cutaneous infarcts which are slow to heal.^{128. and 142.} Electrical burns in the mouth result in irregularly shaped ulcers covered by slough. ¹⁴³ Third-degree burns have been incurred as a result of interferential current therapy used to treat pain and reduce edema. ¹⁴¹

Lightning strikes may be associated with full-thickness burns, linear charring, and branching or ferning marks known as Lichtenberg figures.^{144. and 145.}

Frostbite occurs when tissue freezes. ¹²² Usually, an acral part such as a finger, toe, ear, or even the nose is involved. The affected part becomes white or bluish white. ¹²² A blister forms a day or so after rewarming and this is followed some days later by the formation of a hard eschar. ¹²² Autoamputation of the affected area eventually occurs. The terms ‘chilblain’ and ‘perniosis’ (see p. 235) are used for a specific lesion that may result from exposure to cold temperatures.

Cold injury has resulted from electronic cooling devices attached to the knee after knee surgery in an attempt to decrease postoperative pain and inflammation. ¹⁴⁸ The histological changes were similar to those seen in perniosis. ¹⁴⁸

Cryotherapy using carbon dioxide or liquid nitrogen is commonly used in the treatment of cutaneous tumors and premalignant keratoses. As cryotherapy involves rapid cooling it produces numerous intracellular ice crystals and hence more destruction than does the slow cooling of an area. ¹²²

The effects of cryotherapy on normal skin have been elucidated using volunteers and by studying the skin adjacent to lesions which are removed subsequent to cryotherapy. These studies have shown that different cells vary in their susceptibility to cold injury. ¹²² For example, melanocytes appear to be particularly sensitive to the effects of cold, an explanation for the hypopigmentation that may follow cryotherapy.

Polymorphous cold eruption, a rare, autosomal dominant disorder, is characterized by a non-pruritic erythematous eruption developing after generalized exposure to cold air. ¹⁵² The lesions are usually localized to the face and extremities. The eruption is often accompanied by fever, malaise, and headache. It differs clinically and histologically from cold urticaria, with which it is often confused.

The photosensitive genodermatoses are discussed here for completeness. Several of them have been discussed in other chapters. Most are exceedingly rare.

Phototoxicity is the damage induced by ultraviolet and/or visible radiation as a result of contact with or the ingestion of a photosensitizing substance. ¹⁸⁶ It does not depend on an allergic reaction and is therefore akin to an irritant contact dermatitis. ¹⁸⁷Phytophotodermatitis is a photosensitivity reaction, usually phototoxic in type, which results from contact with plants containing psoralens and other furocoumarins.^{188.189. and 190.} The families Umbelliferae and Rutaceae contain many phototoxic species. ¹⁹¹ They include celery,^{188.192. and 193.} parsnips, carrots, fennel, dill, giant hogweed, zabon (Citrus maxima), ¹⁹¹ limes, and lemons. ¹⁹⁴ Herbal therapies applied to the skin can induce a phytocontact dermatitis. ¹⁹⁵ Phytophotodermatitis in children is sometimes mistaken for child abuse. ¹⁹⁶

Clinically, phototoxic reactions resemble an exaggerated sunburn reaction with dusky erythema; when severe, vesiculation may occur, followed by desquamation and hyperpigmentation.^{197.198. and 199.} Two patterns of reaction are seen: an immediate reaction, which follows the ingestion of the photosensitizing agent and involves exposed areas such as the face, ears, V-area of the neck, and dorsum of the hands; ²⁰⁰ and a delayed reaction, which follows contact with psoralens and peaks after 2 or 3 days. The reaction is limited to the site of contact with the photosensitizing agent. Prominent pigmentation lasting for weeks or months may follow phytophotodermatitis. ¹⁸⁸ In some instances, the preceding erythematous phase may go unnoticed. ¹⁸⁹ Chronic changes include wrinkling, atrophy, telangiectasia, and the formation of keratoses.

Another presumed phototoxic reaction is the formation of subepidermal bullae, first reported in patients with chronic renal failure receiving high doses of furosemide (frusemide). ²⁰¹ Other drugs which may produce this pseudoporphyria reaction (see p. 498) include naproxen, ²⁰² oxaprozin, pravastatin, mefenamic acid, nabumetone, flutamide, dapsone, tetracycline, pyridoxine, nalidixic acid, ²⁰³ and vinblastine. ²⁰⁴ A list of drugs producing photosensitivity reactions has recently been published. ²⁰⁵ Prolonged sunbed exposure of chronically sun-damaged skin has also been incriminated in producing pseudoporphyria, although whether there is any phototoxic component remains to be seen. ²⁰⁶ Photo-onycholysis is another rare complication of certain drugs including indapamide, thiazides, captopril, and sparfloxacin.^{207. and 208.}

Ingested drugs capable of causing a phototoxic reaction include, in addition to those mentioned above, phenothiazines, thioxanthenes, ²⁰⁹ thiazides,^{210. and 211.} doxycycline, ²¹² fleroxacin, ²¹³ ofloxacin, ²¹⁴ sitafloxacin, ²¹⁵ enoxacin, ²¹⁵ sparfloxacin, ²¹⁵ tetrazepam, ²¹⁶ non-steroidal anti-inflammatory drugs, ²¹⁷ voriconazole, ²¹⁸ retinoids, ²¹⁷ amiodarone, ²¹⁹ atorvastatin, ²²⁰ carbamazepine, and sulfonamides.^{197. and 221.} Azathioprine therapy appears to photosensitize skin to subsequent UVA radiation. ²²² Topical agents associated with phototoxicity include coal tar and derivatives, psoralens, ¹⁸⁹ and textile dyes, ²²³ as well as some perfumes and sun barrier preparations. ²²⁴ The causes of a phototoxic dermatitis are listed in Table 21.1. A bullous phototoxic reaction has followed the use of aromatherapy oil containing bergamot which contains furocoumarins. ²²⁵ Tobacco smoke is phototoxic. ²²⁶

A phototoxic reaction requires the absorption of photons of specific wavelengths by the photosensitizing substance. ²²¹ Energy is dissipated as it returns from an excited state to its ground state. Free radicals, peroxides, and other substances are formed which may potentially damage cellular and subcellular membranes.^{221. and 227.} The action spectrum is usually in the UVA range, although with some ingested substances (e.g. thiazides) it is in the shorter UVB wavelengths.^{197. and 210.} The formation of apoptotic keratinocytes (‘sunburn’ cells) appears to require UVB radiation; tumor necrosis factor-α, p53 protein, and other factors are involved in some way.228.^{229. and 230.} There is some evidence that a p53-independent pathway can also be involved. ²³¹ Melanocytes, in contrast, are much more resistant to ultraviolet-induced apoptosis, due to a high level of antiapoptotic proteins such as Bcl-2. This protein is up-regulated by nerve growth factor produced by keratinocytes exposed to UV irradiation. ²³² It is interesting to speculate whether this is the mechanism of the melanocytic hyperplasia seen in chronic sun-damaged skin.

Phototoxicity is more common than photoallergy, from which it differs by being dose related and by its subsidence on removal of the photosensitizer or the ultraviolet radiation. Some drugs produce both toxic and allergic reactions; in others, the mechanism has not been elucidated.

Photodynamic therapy is used, selectively, in the treatment of some cutaneous malignancies. It involves the use of a photosensitizing agent which is applied to, or accumulates in, malignant tissue, followed by the application of a light source that activates the photosensitizer. ²³⁵ This results in the release of toxic oxygen radicals that destroy the malignant cells. Recently, partial-thickness burns have been reported following the ingestion of temoporfin, a second-generation photosensitizer. ²³⁶ Acute phototoxicity with urticarial features has also been reported from photodynamic therapy using topical 5-aminolevulinic acid. ²³⁷

Photoallergy is increased reactivity of the skin to ultraviolet and visible radiation and is brought about by a chemical agent on an immunological basis.^{186. and 234.} The photosensitizing chemical is usually applied topically to the skin; uncommonly, photoallergic reactions may follow ingestion of a drug.^{186. and 238.}

The usual photoallergic reaction develops 24–48 hours after sun exposure and is a pruritic, eczematous eruption. ²³⁹ Lichenification may occur in cases of long standing. Lichenoid papules have been reported in some thiazide-induced photoallergic reactions. ²³⁹ Photoallergic dermatitis occurs essentially on light-exposed areas, although there is a tendency for lesions to extend beyond the exposed areas. Regression usually occurs after 10–14 days, although in some cases the condition may persist for long periods and the patients become persistent light reactors (see below). Topical agents that have been implicated in photoallergic reactions include fragrances such as musk ambrette²⁴⁰ and coumarin derivatives, ²⁴¹ and sunscreens containing benzophenones,^{242.243.244.245. and 246.} oxybenzone, butyl methoxy dibenzoylmethane, ²⁴⁶ methoxycinnamate, ²⁴⁷ or para-aminobenzoic acid and its esters.^{198.224. and 248.} Benzophenones contained in products other than sunscreens can also produce photoallergic reactions. ²⁴⁹ Benzocaine, ²⁵⁰ piroxicam gel, ²⁵¹ ketoprofen, ²⁵² plants in the Compositae family, and, rarely, psoralens have been recorded as producing photoallergic reactions. The halogenated salicylanilides, which resulted in numerous cases of photoallergic dermatitis over two decades ago, have been withdrawn as topical antibacterial agents. ²⁵³ Systemically administered drugs which rarely produce photoallergy include quinine,^{254. and 255.} quinidine,^{256. and 257.} griseofulvin, possibly itraconazole,^{258. and 259.} ranitidine,^{260. and 261.} lomefloxacin, ²⁶² chlorpromazine, ²⁶³ piroxicam,^{264.265. and 266.} ampiroxicam, ²⁶⁷ droxicam, ²⁶⁸ piketoprofen, ²⁶⁹ ketoprofen,^{270. and 271.} voriconazole,^{218. and 272.} pyridoxine hydrochloride (vitamin B₆),^{273. and 274.} tegafur, ²⁷⁵ flutamide,^{276. and 277.} alprazolam, ²⁷⁸ sertraline (Zoloft), quinapril, ²⁷⁹ triflusal, ²⁸⁰ nifedipine, ²⁸¹ amlodipine,^{281. and 282.} thiazides, sulfonamides, ²⁸³ capecitabine, ²⁸⁴ celecoxib, ²⁸⁵ certain tetracycline derivatives, diphenhydramine, ²⁸⁶ tolbutamide, ibuprofen, ²⁸⁷ herbal treatments, ²⁸⁸ fibric acid derivatives (such as fenofibrate and clofibrate),^{289.290. and 291.} chlordiazepoxide, and cyclamates.^{224. and 234.} The author’s experience of the more common drugs producing photosensitive reactions over the last 5 years is shown in Table 21.2. These observations are based on the consequences of drug cessation but not subsequent rechallenge. Drugs which may produce a lichenoid photoallergic reaction include, in addition to thiazide diuretics (see above), demeclocycline, enalapril, quinine, quinidine, and chloroquine. ²¹⁷ A flagellate dermatitis, resembling that produced by bleomycin (see p. 394), has been reported after the ingestion of raw shiitake mushrooms.^{292. and 293.} A photo-distributed pustular drug eruption, with overlap features between Sweet’s syndrome and acute generalized exanthematous pustulosis, has been associated with antidepressant therapy. ²⁹⁴ The various drugs producing photoallergic reactions are listed in Table 21.3.

Three factors are required in a photoallergic reaction: a photosensitizing agent, light (usually in the UVA range), and a delayed hypersensitivity response. ¹⁸⁶ The absorption of light energy appears to alter the photosensitizing chemical in some way to produce a hapten which attaches to a protein carrier and eventually stimulates immunocompetent cells, producing a hypersensitivity response. ²²¹ Photopatch testing is used to elucidate the offending agent. ²⁹⁵ The standard set of photoallergens has to be updated periodically to accommodate changing formulary of topical preparations. ²⁹⁶

Hydroa vacciniforme is a rare, debilitating photodermatosis of unknown pathogenesis. ²⁹⁷ It is manifested clinically by the development of erythema and vesicles, on uncovered skin, within 1–2 days of sun exposure.^{297. and 298.} The vesicles heal leaving varioliform scars. Ear mutilation has been reported as a consequence of recurrent lesions with scarring.^{299. and 300.} Oral lesions have been reported.^{301. and 302.}Rarely, there are crusted, non-vesicular lesions. ³⁰³ The disease usually begins in childhood and runs a chronic course before remitting in adolescence. ³⁰⁴ Late onset³⁰⁵ and familial cases are exceedingly rare.^{306. and 307.} Coexistence with a malignant lymphoma has been documented. ³⁰⁸ Porphyrins are normal. Lesions may be reproduced in many instances by repeated exposures to UVA radiation.^{309.310.311.312. and 313.} Dietary fish oil, which provides some systemic photoprotection, has produced variable clinical responses in this disease. ³¹⁴

About 10 years ago, attention was drawn to a hydroa vacciniforme-like eruption associated with latent Epstein–Barr virus (EBV) infection, which had a high propensity to develop cutaneous lymphoma, usually of subcutaneous type.^{315.316.317. and 318.} Latent EBV infection has now been detected in the dermal infiltrate of children with typical manifestations of hydroa vacciniforme.^{315. and 319.} Often, cases associated with EBV have lesions on both sun-exposed and protected areas of the body but there are several reports of EBV-associated hydroa vacciniforme limited to the face. ³²⁰ Severe cases are often associated with NK-cell lymphocytosis, hypersensitivity to mosquito bites, and fatal hemophagocytic syndrome. Progression to NK/T-cell lymphoma is another cause of death in these severe cases. ³²¹ It has been suggested that both the typical and atypical forms are part of a spectrum, in which the atypical lesions have the potential to lead to an EBV-associated lymphoid malignancy.^{315. and 322.} Lesions of hydroa vacciniforme can be induced in patients with latent EBV infection by repeated UVA irradiation. ³²³

The exact status of hydroa estivale is uncertain.^{324. and 325.} It has been regarded in the past as a mild form of hydroa vacciniforme or a childhood form of polymorphic light eruption. ³⁰⁹ Some of the earlier reported cases may have been erythropoietic protoporphyria.^{326. and 327.}

Polymorphic light eruption (polymorphous light eruption) is an idiopathic photodermatosis in which lesions of varied morphology appear several hours or even days after exposure to the sun and subside in a further 7–10 days if further exposure is avoided.^{329.330.331. and 332.} Certain populations appear to be genetically predisposed: in Finland, cases with an autosomal dominant mode of inheritance, with reduced gene penetrance, have been reported. ³³³ Twin studies and genetic modeling have also established a clear genetic influence.^{334.335. and 336.} Polymorphic light eruption affects 10–20% of those living in temperate climates;^{331.337. and 338.} it is much less common in populations living nearer to the equator. ³³⁹ The prevalence in the northern hemisphere is about 15%. It is very uncommon in subtropical Brisbane, Australia (author’s personal experience), yet it is not uncommon 1000 miles to the south. ³⁴⁰

The lesions may take the form of small pruritic papules, papulovesicles, or urticarial plaques. ³⁴¹ The papulovesicular form (pinpoint papular variant) has been regarded as a discrete subset.^{342.343. and 344.} Rarely, lesions may resemble those seen in erythema multiforme or insect bites. ³⁴¹ Eczematous lesions and lesions resembling those of prurigo nodularis³⁴⁵ have been described,^{346. and 347.} although these variants are not universally accepted as part of the spectrum of polymorphic light eruption. ³⁴¹ Lesions are usually monomorphous in the same individual. ³⁴⁸ The severity of the disease is highly variable. ³⁴⁹ Sun-related pruritus may rarely precede the onset of the disease. ³⁵⁰ Contact and photocontact allergies are present, rarely, in patients with polymorphic light eruption. ³⁵¹

Lesions have a predilection for the dorsum of the hands and forearms, the upper part of the arms, the neck, and the face. ³⁵² The face is usually spared in the papulovesicular form. The photodermatosis known as ‘juvenile spring eruption of the ears’, a condition found predominantly in young boys, is a probable variant of polymorphic light eruption. ³⁵³‘Lambing ears’, a blistering and crusting disorder of the pinnae of farmers at lambing time, is a variant of juvenile spring eruption with unusual demographics. ³⁵⁴ The mean age of onset of polymorphic light eruption is in the third decade of life. ³⁵⁵ In most series there has been a female preponderance.^{341. and 356.}

Various associations have been reported, some of which may be fortuitous. They include common variable hypogammaglobulinemia, ³⁵⁷ thyroid disease, ³⁵⁸ and lupus erythematosus.^{359.360. and 361.} A recent study of patients with elevated titers of antinuclear antibodies with polymorphic light eruption found no progression to lupus erythematosus in any of the patients after a median follow-up period of 8 years. ³⁶² Lesions have rarely been limited to areas of vitiligo³⁶³ or nevoid telangiectasia. ³⁶⁴ Psychological distress has been reported in more than 40% of individuals with the disease. ³⁶⁵

The condition is chronic in nature, although in about half the cases there is diminished sensitivity to sunlight over time, with periods of total remission; light sensitivity increases in some patients.^{355.366.367. and 368.} The phenomenon of eventual tolerance to sunlight is known as ‘hardening’. ³⁶⁹ Accordingly, prophylactic phototherapy using PUVA therapy is used in the treatment of the disease. ³⁷⁰ Some studies suggest that a delayed hypersensitivity reaction to sunlight-modified skin antigens is involved in the pathogenesis.^{371.372. and 373.} Put in another way, polymorphic light eruption is an autoimmune disease against an ultraviolet radiation-induced cutaneous antigen. ³⁷⁴ In normal subjects, ultraviolet exposure leads to a disappearance of Langerhans cells from healthy skin 48–72 hours later and an accumulation of CD11b⁺ (Mac1) macrophage-like cells, which reportedly produce interleukin-10. In patients with polymorphic light eruption, Langerhans cells do not disappear after ultraviolet exposure and CD11b⁺ cells, already present at the time of exposure, further increase and invade the epidermis. ³⁷⁵ There is a reduced expression of TNF-α, IL-4, and IL-10 in the UVB-irradiated skin of patients with polymorphic light eruption which is largely attributable to a lack of neutrophils, and is indicative of reduced Langerhans cell migration. ³⁷⁶ In short, there is a defect of UV-induced immunosuppression in this disease. ³⁷⁷ There is normalization of UVB-induced trafficking of Langerhans cells and neutrophils after artificial UVB ‘hardening’. ³⁷⁸ The action spectrum appears to be quite broad and may involve both the UVA and UVB range,^{379.380.381. and 382.} although UVA radiation appears to be the more important.^{339.383. and 384.} There is no significant relationship between the ease of provocation of the disease by UVA and/or UVB radiation and clinical disease severity. ³⁸⁵

The management of polymorphic light eruption primarily involves preventative measures such as avoidance of sun exposure and use of sunscreens with high UVA protection. ³⁸⁶ The use of phototherapy in an attempt to produce ‘hardening’ has been mentioned above. Systemic immunosuppression may be required in severe cases. ³⁸⁶

Actinic prurigo (Hutchinson’s summer prurigo, ³⁹⁵ hereditary polymorphic light eruption)^{396. and 397.} is a chronic photodermatitis occurring predominantly in North American Indians and in Central America, although people of European origin and Asians are not spared.^{398.399.400.401.402.403. and 404.} Actinic prurigo has been regarded as a variant of polymorphic light eruption, ³⁹⁸ although this has been challenged on the basis of its distinct HLA typing. ⁴⁰⁵ It is possible that the characteristic actinic prurigo phenotype is determined by this HLA type (DRB1*0407), found in 70% of patients.^{404. and 406.} An association with DRB1*14 has been reported in an Inuit population. ⁴⁰⁷ Both actinic prurigo and polymorphic light eruption may share a common pathophysiological basis.^{335.408. and 409.} Families with members having either disease have been reported.^{335. and 410.} Light testing gives inconsistent results although the majority are sensitive to UVA light.

Actinic prurigo is characterized by onset in childhood, female preponderance, a familial tendency, which is quite high in some communities, and severe pruritus.^{398.399. and 411.} It appears to be inherited as a dominant trait but with incomplete penetrance. ⁴¹² It commences as an eczematous eruption on exposed areas, particularly the face, earlobes, and forearms. ³⁹⁶ Covered areas are involved in some patients, but not others. ⁴¹³ Papular, plaque-like and prurigo-like papulonodules develop. ³⁹⁹ Lichenification and postinflammatory scarring can be marked. ⁴⁰⁴ Other features that may be present include an exudative and crusted cheilitis of the lower lip, ⁴¹⁴ conjunctivitis, ⁴¹⁵ and alopecia of the eyebrows. ³⁹⁸ Primary cutaneous B-cell lymphoma has developed in two patients. ⁴¹⁶