Photodermatitis

Essentials

• Ultraviolet (UV) radiation from the sun or, more rarely, visible light can provoke a rash either
  • alone without contributing factors (idiopathic photodermatitis)
  • in combination with an ingested or externally applied medicine
  • in combination with a chemical substance on the skin (e.g. phytophotodermatitis associated with plant contact)
• UV radiation may also trigger certain skin conditions or worsen their symptoms.
• Protection against the sun is paramount as is the avoidance of known offenders.
• Treatment consists of glucocorticoids either topically or orally, or of antihistamines for solar urticaria.

Idiopathic photodermatitis

• Polymorphous light eruption (PMLE; picture 1)
  • By far the most common form, more common in women. Prevalence varies from country to country and may be up to 15-20% in some populations.
  • Onset usually at the age of 20-30 years; may resolve over the years.
  • Typically encountered in the spring and early summer, with symptoms occurring within a few hours of UV exposure and continuing for a few days, sometimes longer.
  • Itchy papules, vesicles or plaques most often on the backs of the hands, forearms and chest. Juvenile spring eruption is a subtype, which causes vesicles on the auricles in young boys.
  • In some patients, tolerance to the sun will increase as the summer progresses, and they will have no symptoms towards the end of the summer. However, the symptoms will recur the next spring/summer.
  • Rare subtypes of PMLE include hydroa vacciniforme occurring in children and causing blisters in areas exposed to light and actinic prurigo occurring particularly in American Indians.
• Solar urticaria
  • A rare form of physical urticaria
  • Occurs as urticarial wheals or in some cases as just itching and erythema on sun exposed skin areas, occasionally as a result of minimal sun exposure.
  • Symptoms develop within minutes, and resolve in a few hours.
  • Tolerance will increase but not to the same degree as in PMLE. In a small share of patients, the symptoms resolve over the years.
• Chronic actinic dermatitis
  • Uncommon, occurs mainly in elderly men.
  • Photosensitivity and chronic eczema in light exposed areas that may spread to other skin areas
  • Often in people with a history of a chronic skin condition (atopic eczema or contact allergy to metals or perfumes, for example).
  • Symptoms erupt slowly and may progress to cutaneous lymphoma.

Photodermatitis induced by medicines or chemicals

• Exposure to an exogenous substance combined with UV radiation may cause a photoirritant (phototoxic) reaction or a photoallergic reaction.
• The photosensitising substance can sometimes be an endogenous origin metabolite (see porphyrias Porphyrias).

Diseases exacerbated by light

• Symptoms also occur in the absence of light but are triggered or worsened by light.
  • Rosacea Rosacea
  • Herpes Herpes Simplex Infection of the Skin
  • Vitiligo Vitiligo
  • Systemic lupus erythematosus (SLE) Systemic Lupus Erythematosus (Sle), cutaneous lupus erythematosus Discoid Lupus Erythematosus and dermatomyositis Myositis
  • Some other rare diseases, such as xeroderma pigmentosum http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Lng=GB&Expert=910

History and clinical picture

• The history is the most important aspect of diagnosis, particularly in the diagnosis of PMLE and solar urticaria.
• A drug history should be obtained, as well as a history of possible exposure to chemicals or plants.
• Photodermatitis or drug-induced photodermatitis can be suspected if the rash is limited to the areas of skin exposed to light. Unexposed areas are often unaffected (inner aspect of the arms, under the jaw, behind the ears and all areas covered by clothing).
• An important piece of information for differential diagnosis is how long it took for the symptoms to erupt when the patient was exposed to sun, and how long it took for them to disappear after the end of sun exposure (minutes in solar urticaria, hours-days in PMLE, days-weeks in chronic actinic dermatitis).
• The appearance of the rash differs between the different types of photodermatitis: erythema, urticaria, papules, vesicles, blisters, eczema, lichenification.
• Increased tolerance as the summer progresses
  • Characteristic especially in PMLE, but hardly ever occurs in drug-induced photodermatitis.
• Photodermatitis often has a typical age of onset.
  • Childhood
    • PMLE, especially juvenile spring eruption
    • Childhood porphyrias, especially erythropoietic porphyria http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=79278
    • Photocontact dermatitis
  • Early adulthood
    • PMLE
    • Drug-induced photodermatitis
    • Solar urticaria
    • Photocontact dermatitis
    • (Chronic actinic dermatitis)
    • Rosacea Rosacea
    • SLE Systemic Lupus Erythematosus (Sle) and cutaneous lupus erythematosus Discoid Lupus Erythematosus
    • Porhyrias (porphyria cutanea tarda, variegate porphyria) Porphyrias
  • Later adulthood
    • Chronic actinic dermatitis
    • Drug-induced photodermatitis
    • Photocontact dermatitis
    • Dermatomyositis Myositis

Diagnosis and differential diagnosis

• Specific phototests are very rarely indicated
  • Only in tertiary care hospitals and some secondary level hospitals
• Epicutaneous tests are important in the diagnostic workup if photodermatitis with eczematous symptoms is suspected.
  • Contact allergies (particularly to cosmetics) are important in differential diagnosis.
  • In chronic actinic dermatitis, the patient often has a history of contact allergy, for example to metals, rubber or plant chemicals.
• The possibility of a disease aggravated by light must be borne in mind, and specific tests may be indicated.
  • Blood tests, such as basic blood count with platelet count and autoimmune serological tests (antinuclear antibodies, at least); see also SLE Systemic Lupus Erythematosus (Sle) and cutaneous lupus erythematosus Discoid Lupus Erythematosus, porphyria tests (diagnostics, see Porphyrias),
  • Skin biopsy

Treatment