What are the causes, symptoms, and treatment options for photodermatoses, particularly in fair-skinned individuals?

Photodermatoses: Classification, Causes, Symptoms, and Treatment

Classification

Photodermatoses are skin disorders induced or exacerbated by ultraviolet radiation, classified into four main categories: 1, 2

• Immunologically mediated (idiopathic) photodermatoses - including polymorphic light eruption (PLE), actinic prurigo, chronic actinic dermatitis (CAD), solar urticaria (SU), and hydroa vacciniforme 1, 2
• Drug- and chemical-induced photosensitivity - both phototoxic and photoallergic reactions 1, 2
• Photodermatoses secondary to endogenous agents - primarily the porphyrias 2
• Photoaggravated dermatoses - including autoimmune diseases, infectious conditions, and nutritional deficiencies 2
• Genetic disorders with defective DNA repair 1, 2

Causes and Pathomechanisms

Immunologically Mediated Photodermatoses

These represent the most common photosensitive disorders, though the exact pathomechanism remains unclear. 1

• Chronic UV radiation exposure triggers abnormal immune responses in genetically predisposed individuals 1, 3
• Fair-skinned individuals are at highest risk - those with freckling, light hair/eye color, and tendency to burn rather than tan 4
• UVB-specific mutations have been demonstrated in sun-damaged skin, providing molecular evidence for UV causation 5

Drug and Chemical Photosensitivity

• Thiazide diuretics (particularly hydrochlorothiazide) contain sulfonamide groups that absorb UVA radiation, generating reactive oxygen species causing DNA damage 4
• High UV environments exponentially increase photosensitization risk from medications 4

Clinical Features and Symptoms

Polymorphic Light Eruption (Most Common)

PLE affects 10-20% of the population and presents with characteristic lesions on sun-exposed skin. 6

• Lesions appear hours to days after sun exposure on face, neck, chest, and dorsal hands 1, 7
• Symptoms include pruritus, erythema, and papulovesicular eruptions 5
• Lesions may be asymptomatic but occasionally sore or itchy 5

Chronic Actinic Dermatitis

• Severe photosensitivity with eczematous changes on exposed areas 5
• May extend to covered areas in severe cases 5

Solar Urticaria (Rare)

• Immediate urticarial response within minutes of sun exposure 5
• Prevalence approximately 0.34 per 100,000 6

Actinic Keratoses

• Discrete patches of erythema and scaling on chronically sun-exposed skin (face, dorsal hands) in middle-aged and elderly fair-skinned individuals 5
• Often asymptomatic but may be sore or pruritic 5
• Represent premalignant lesions with low individual potential for invasive squamous cell carcinoma 5

Diagnostic Evaluation

Clinical recognition of characteristic lesions localized predominantly in light-exposed skin is the starting point. 1

Essential History Elements

• Duration of lesions and temporal relationship to sun exposure 1, 7
• Changes in size, color, or shape 5
• Symptoms: itching, burning, bleeding 5, 1
• Medication history - particularly thiazides, NSAIDs, antibiotics 7
• Family history of photosensitivity or skin cancer 5, 2

Physical Examination

• Distribution pattern - predominantly sun-exposed areas (face, neck, dorsal hands, forearms) with sparing of photo-protected sites 1, 7
• Morphology of eruption - papules, vesicles, plaques, or urticaria 2
• Presence of irregular margins, irregular pigmentation, or ulceration 5

Specialized Testing

• Phototesting - determines minimal erythema dose (MED) and minimal urticarial dose (MUD) to UVA and UVB 1, 2
• Photopatch testing - essential for suspected photoallergic reactions 1, 2
• Skin biopsy - may be required for atypical presentations 2
• Laboratory investigations - ANA panels for autoimmune disease, porphyrin profiles for porphyrias 2

Treatment Approach

First-Line: Photoprotection (All Photodermatoses)

Photoprotection is essential for all photodermatoses and forms the foundation of management. 8, 7

• Apply broad-spectrum sunscreens with SPF ≥30 (or ≥15 per British guidelines) with high UVA protection daily to all sun-exposed areas 8, 4
• Avoid sun exposure during peak UV hours (10 AM to 4 PM) and seek shade when outdoors 8, 4
• Wear photoprotective clothing, wide-brimmed hat, and sunglasses 4, 7

Acute Management of Active Lesions

For provoked eruptions, potent topical corticosteroids should be applied to active lesions. 8

• Topical betamethasone or hydrocortisone butyrate for trunk lesions 5
• 1% hydrocortisone for facial lesions 5
• Oral prednisolone (40-50 mg) for severe acute flares 5, 8

Prophylactic Phototherapy (Second-Line for Moderate-to-Severe Disease)

Phototherapy is indicated for patients with moderate-to-severe PLE who experience substantial quality of life impairment despite optimal photoprotection. 8

Narrowband UVB vs. PUVA

For young adult females and patients concerned about long-term skin cancer risk, narrowband UVB should be preferred over PUVA despite comparable efficacy. 8

• Both modalities show 88-89% good or moderate improvement in a 10-year retrospective review of 170 patients 5, 8
• NB-UVB has lower long-term skin cancer risk compared to PUVA 8
• NB-UVB causes more frequent rash provocation (62% vs 12-50%) and erythema (54% vs 8-67%), but comparable pruritus 5, 8

PUVA Protocol

• Administer twice weekly (UK standard) in early spring for 12-20 treatments 5, 8
• Timing is critical: early spring administration maintains photoprotection through mid-summer 5, 8
• Starting dose: 8-MOP at 70-80% of minimal phototoxic dose 5

Critical Precautions During Phototherapy

The risk of provoking PLE is high (12-50% with PUVA, 48-62% with UVB), particularly during initial exposures. 5, 8

• Prophylactic oral prednisolone (40-50 mg) for the first 2 weeks of phototherapy 5, 8
• Routine prophylactic application of potent topical corticosteroid after each exposure 5, 8
• Use small dose increments (0.05 J/cm²) especially in the initial phase 5, 8
• If provocation occurs, manage with potent topical steroid and lower subsequent dose increments 5

Special Considerations for Chronic Actinic Dermatitis

PUVA therapy for CAD should only be undertaken in specialist units experienced in managing this disease. 5

• Requires inpatient supervision and topical/oral corticosteroid cover 5
• Prednisolone (20-30 mg) taken on day of phototherapy 5
• Very small dose increments (0.05 J/cm²) with each UVA exposure 5
• Treatment given three times weekly, then reduced to twice weekly, then once weekly 5

Solar Urticaria Management

For solar urticaria, high-dose H1 antihistamines are first-line pharmacotherapy, though substantial proportions receive only modest benefit. 5

• PUVA or NB-UVB can be considered when antihistamines fail 5
• Starting dose: 80% MUD or 0.25 J/cm² (whichever lower) three times weekly for 4-8 weeks 5
• UVA alone may be considered if patients have very low MUD for UVA, offering reduced acute phototoxic reaction risk 5

Post-Phototherapy Maintenance

Continued natural sunlight exposure is essential post-treatment to maintain photoprotection through summer. 5, 8

• The photoprotective effect diminishes or is lost several weeks post-phototherapy 5
• Annual desensitization is generally not recommended due to cumulative skin carcinogenesis risk 5, 8

Long-Term Monitoring and Skin Cancer Surveillance

Patients receiving >150-200 PUVA exposures require annual skin cancer surveillance. 8

• The benefit of repeated phototherapy courses must be weighed against long-term skin carcinogenesis risk 5, 8
• Annual dermatologic examination of all sun-exposed areas is recommended 4
• Immediate reporting of any suspicious lesions - changes in size, color, shape, or new symptoms 4

Common Pitfalls and Caveats

Timing of Phototherapy

Administering phototherapy too early in the year results in subsided photoprotection by mid-summer; too late increases risk of provocation. 5

• Optimal timing: early spring in temperate climates 5, 8

Drug-Induced Photosensitivity Management

For patients on thiazide diuretics with fair skin or existing actinic keratoses, consider alternative antihypertensives. 4

• ACE inhibitors or ARBs offer equivalent cardiovascular benefits without photosensitizing properties 4
• Bendroflumethiazide is not meaningfully associated with increased skin cancer risk and represents a safer thiazide alternative 4

Actinic Keratoses Treatment Selection

Treatment choice depends on lesion number, thickness, location, and patient characteristics. 5

• For low numbers of thin AKs: cryosurgery or 5-fluorouracil 5
• For high numbers or confluent AKs: 5-fluorouracil, imiquimod, or photodynamic therapy 5
• For hypertrophic or isolated lesions failing other therapies: curettage with histology 5
• Below-knee lesions: photodynamic therapy preferred due to poor healing concerns 5