Photodermatoses

Photodermatoses (photosensitivity disorders) are a group of skin conditions that result from an abnormal reaction to UV light and can be categorized as either primary or secondary photodermatoses depending on the specific cause. Primary photodermatoses are induced by immune-mediated reactions (e.g., as in polymorphous light eruption) or stem from chemical/drug exposure. Secondary photodermatoses result from underlying disorders (e.g., genetic diseases, photoaggravated dermatoses) that increase an individual's susceptibility to adverse UV reactions. Most photodermatoses present as an erythematous rash on areas of sun-exposed skin. A careful history and full skin examination are required to differentiate between the types. In the case of diagnostic uncertainty, further workup includes laboratory studies for underlying causes, skin biopsy, and phototesting. The general management of photodermatoses for both adults and children involves supportive therapy for symptom relief, photoprotective measures, and avoidance of triggers (e.g., phototoxic agents). Further treatment, if required, is usually overseen by a specialist and may include phototherapy and immunosuppressive therapy.

The diagnosis and management of sunburn are discussed in a separate article.

Primary photodermatoses ^[1][2][3]

• Immune-mediated
  • Polymorphous light eruption (PMLE)
  • Hydroa vacciniforme
  • Chronic actinic dermatitis
  • Actinic prurigo
  • Solar urticaria
• Drug or chemical induced
  • Phototoxic reactions: drug-induced phototoxic reactions, phytophotodermatitis
  • Photoallergic reaction

Secondary photodermatoses ^[4]

• Photoaggravated dermatoses
  • Systemic lupus erythematosus (SLE)
  • Dermatomyositis
  • Acne vulgaris
  • Herpes simplex
  • Lichen planus actinicus
• Genetic disorders
  • Porphyria cutanea tarda
  • Xeroderma pigmentosum
• Neoplastic disorders
  • Actinic keratosis
  • Melanoma and nonmelanoma skin cancers

General principles

• Most photodermatoses present as an erythematous rash in sun-exposed areas.
• Careful history-taking is usually sufficient to establish a clinical diagnosis; further studies are reserved for diagnostic uncertainty.
• The initial general management of photodermatoses is the same for all forms of the disease.

Clinical evaluation

• Focused history ^[1]
  • Time since exposure to sun or artificial light
  • Use of medications, creams/cosmetics, or contact with plants
  • History of intense pruritus
  • Symptom improvement during the winter months and with less exposure to the sun
  • Family history of photodermatoses
• Physical examination
  • Erythematous rash and swelling on sun-exposed areas (e.g., face, upper neck, or back) ^[1][2]
  • Possible primary skin lesions (e.g., vesicle, blister)

The rash in photodermatoses usually spares skin folds and areas covered with jewelry or clothes. ^[2]

Diagnostics of photodermatoses ^[2][4][5]

• Photodermatoses are typically a clinical diagnosis. ^[1]
• For diagnostic uncertainty:
  • Consider laboratory studies, e.g.:
    • Plasma porphyrins for porphyria cutanea tarda
    • ANA, anti-Ro, and anti-La antibodies for SLE
  • Perform a skin biopsy.
  • Consider challenge-rechallenge testing, where a suspected agent is withdrawn and then reintroduced to see if a recurrence occurs.
  • Refer to a specialist for phototesting and/or additional studies to evaluate for secondary photodermatoses.

Phototesting ^[2][5]

• Definition: a collection of studies that assess the reaction of the skin when exposed to UV radiation
• Indication: diagnostic confirmation for patients with suspected primary photodermatoses
• Methods
  • Minimal erythema dose (MED) testing
    • Different skin fields are exposed to increasing UV doses to determine the threshold dose to trigger.
    • Serial readings of the erythema are indicated every few hours.
  • Photoprovocation test
    • A test that aims to reproduce photodermatoses
    • Performed by repeatedly exposing a patient to fixed doses of UV radiation for a period of at least 3 days
  • Photopatch testing
    • A study used to identify photoallergens
    • Suspected agents are applied to the skin in duplicate sets, with one set being exposed to UV radiation and the other not exposed and used for control.

Phototesting is not always available and challenge-rechallenge testing may be required as an alternative. ^[2]

General management of photodermatoses

• Start supportive therapy for photodermatoses. ^[4][6]
  • Pruritus: Recommend antihistamines and cold compresses.
  • Erythema: Consider topical corticosteroids.
• Advise patients to avoid UV radiation; when possible and use photoprotective measures if exposure is unavoidable. ^[5][7][8]
• When possible, stop medications that may be contributing to phototoxic or photoallergic reactions.
• Refer patients to a specialist (e.g., dermatologist, immunologist) if symptoms persist.

Immune-mediated (idiopathic) photodermatoses result from an abnormal immune response to UVR exposure. Polymorphous light eruption is the most common type of immune-mediated photodermatosis and the most ubiquitous photodermatosis overall; other forms of immune-mediated photodermatoses are comparatively rare. ^[2]

Etiology ^[5]

An acquired photodermatosis characterized by a pathological response to UV exposure

Epidemiology

• Most common type of photodermatoses in both adults and children ^[1][2]
• Predominantly affects genetically-predisposed individuals and those with a darker skin tone ^[2][3][4]
• Typically worse during the spring and summer ^[5]

Pathophysiology ^[2]

• Most likely a cell-mediated immune response resembling a delayed-type hypersensitivity reaction
• Presumably caused by a reaction to autoantigens that arise from UV exposure

Clinical features ^[2]

• Erythematous rash
  • Papules, plaques, and vesicles may be present.
  • Usually pruritic
• Common sites involved:
  • Sun-exposed areas
  • Ears in children; this variant is known as juvenile spring eruption.
• Develops minutes to hours (can be days) after the first high-intensity UV exposure in the spring or the summer
• Without continuous sun exposure: resolves within a week
• Symptoms usually:
  • Improve over the summer because of UVR-induced immunologic tolerance (photohardening)
  • Recur annually (always at the same anatomical sites and after the first sun exposure)

Diagnostics ^[2][5]

• PLE is primarily a clinical diagnosis.
• See also “Diagnostics of photodermatoses.”
  • Skin biopsy findings include spongiosis, cellular infiltration predominantly with lymphocytes, and possible vesiculation. ^[5]
  • Results from MED testing and photopatch testing are typically normal. ^[2]

Management ^[5]

• Start general management of photodermatoses, including photoprotective measures.
• Refer to a dermatologist for additional management, which may include:
  • Corticosteroids (oral or topical) ^[1][4]
  • Phototherapy to accelerate photohardening
    • Preferred: narrowband UVB phototherapy ^[1][5]
    • Alternative: PUVA therapy ^[1][5]
  • Immunosuppressive agents (e.g., azathioprine, cyclosporine) for refractory disease

Starting phototherapy in the spring can help prevent symptoms during the summer. ^[4]

• Description: rare photodermatosis that is associated with photosensitivity and a persistent eczematous rash ^[2]
• Epidemiology: more common in adults > 50 years of age with dark skin ^[2]
• Etiology: can occur following chronic episodes of photoallergic contact dermatitis ^[2]
• Clinical features ^[2]
  • Severe, persistent, eczematous eruption with distinct lichenification, itching, scales, and erosions
  • Persistent light reactivity to visible UVB (with or without UVA) light
• Diagnostics: See “Diagnostics of photodermatoses.”
• Differential diagnosis: cutaneous T-cell lymphoma, photosensitivity with HIV infection ^[2][3][5]
• Management: general management of photodermatoses, topical or oral immunosuppressive therapy, PUVA therapy ^[5][9]

• Description: rare photodermatosis that predominantly affects children with indigenous heritage in the Americas ^[2]
• Etiology: UVR exposure in individuals with genetic susceptibility (HLA-DRB1∗0407) ^[2]
• Clinical features ^[2][3]
  • Papular rash which may coalesce into plaques, affecting sun-exposed areas
  • Cheilitis, conjunctivitis, and photophobia may also be present.
• Diagnostics: See “Diagnostics of photodermatoses.”
• Management: general management of photodermatoses, immunosuppressive therapy, and thalidomide in severe cases ^[5][10]

• Description: a rare form of chronic urticaria that predominantly affects adults ^[2]
• Etiology: IgE-mediated type I hypersensitivity reaction ^[2]
• Clinical features ^[2]
  • Urticaria that occurs within minutes of sun exposure and typically resolves within 24 hours of avoiding UVR
  • May be accompanied by angioedema and systemic symptoms (e.g., headache, wheezing)
• Diagnostics: See “Diagnostics of photodermatoses.”
• Management ^[5][11]
  • General management of photodermatoses, antihistamines, phototherapy
  • Refractory cases: immunosuppressive therapy, IVIG, and omalizumab

Chemical sunscreen does not block long-wavelength UV light or visible light, both of which may trigger solar urticaria. Mineral sunscreen should be used instead. ^[5]

• Description: very rare chronic photodermatitis characterized by a vesiculopapular rash of the skin ^[2]
• Epidemiology: mostly children ^[2]
• Clinical features: livid red erythema with serous-filled and hemorrhagic, umbilicated bullae that heal with varioliform scarring ^[2]
• Diagnostics: See “Diagnostics of photodermatoses.”
• Management: general management of photodermatoses, beta-carotene, phototherapy ^[5][12]

Overview

• Drug or chemical-induced photodermatoses are those caused by exposure (either topical or oral) to a photosensitizer
• Photosensitizers may be either phototoxic agents or photoallergens
• While the etiology, pathophysiology, and clinical features vary between the conditions, the diagnostics and management are the same.

Phytophotodermatitis can typically be differentiated from sunburn by a longer latency period before erythema develops, and the pattern of the rash, which is usually localized rather than generalized.

Diagnostics ^[2]

• Primarily a clinical diagnosis ^[8]
• Diagnostic uncertainty: See “Diagnostics of photodermatoses.” ^[2]
  • Skin biopsy findings ^[2]
    • Phototoxic reaction: keratinocyte necrosis and infiltration of neutrophils and lymphocytes
    • Photoallergic reaction: acute spongiotic dermatitis
  • Photopatch testing ^[2]
    • Patients with allergic contact dermatitis will react on both the control and UV-exposed patch.
    • Patients with photoallergy will react only on the UV-exposed patch.

Phytophotodermatitis is the most common phototoxic reaction in children. ^[1]

Management ^[2][8]

• If possible, avoid exposure or discontinue the phototoxic agent or photoallergen. ^[1]
• Start general management of photodermatoses; note, some sunscreens can cause a photoallergic reaction. ^[1]
• For skin exposed to a phytophototoxin: Rinse the skin with water within 2 hours of exposure to reduce the intensity of the reaction. ^[8]
• Severe phototoxic reactions (> 30% body surface area estimation): Consider hospitalization for intense wound care. ^[8]

Sunscreen can cause photoallergic reactions; patients should avoid products containing common photoallergens such as oxybenzone and dibenzoylmethanes. ^[2]