Solar urticaria L56.3

Merklen, 1904; Duke coined the term "solar urticaria" in 1923 (cited by S. Goetze).

A rare, highly acute, IgE-mediated photodermatosis characterized by the development of erythema and wheals on the exposed skin within 5–10 minutes of light exposure. These symptoms subside without leaving any residual effects after about 30–60 minutes, provided further sun exposure is avoided (Gaebelein-Wissing N et al. 2020).

The nature and severity of the condition depend on the duration of exposure, the type of sunlight, and the location and extent of the sun-exposed skin areas. Delayed reactions occurring more than an hour (1–5 hours) after exposure have also been reported, as well as anaphylactic reactions (following whole-body exposure), which may involve the oral mucosa. 

Some authors divide the light urticaria into 5 groups according to the UV-spectrometer that triggers them:

• type I (UVB): 280-320nm
• Type II(UVA): 320-400nm
• Type III type V: 400-800 nm

0.08% of urticaria cases/4-8% of all photodermatoses (Navarro-Trivino FJ et al. 2023). This disease is not observed in populations with a dark-skinned population.

IgE-mediated, immediate-type allergic reaction to an unknown, photoinduced autoallergen; a “serum factor” plays a role in some patients. It is assumed that incident light is absorbed by a chromophore. This chromophore is activated to become a photoallergen against which an IgE antibody is directed. The IgE antibody is located on the surface of the mast cell. Binding of the photoallergen subsequently leads to the release of histamine and the formation of wheals.   

The action spectrum can span the entire UV range. However, it is predominantly in the UVA wavelength range (especially UVA-1; Gaebelein-Wissing E et al. 2020).wavelength range, less commonly in the UVB wavelength range (approximately 40% of patients) and in the visible light spectrum (400–600 nm). Triggering by infrared radiation is less common. Some patients report a history of urticaria.   

Mostly occurring in young adults (predominantly 20 to 40 years of age), rarely in old age (7 to 8 decades of age) or in infancy (1 to 6 years of age).

Erythema and wheals developing in the exposed areas within a few minutes of light exposure. The skin symptoms subside within minutes to hours after exposure ends. Subjectively, patients experience extremely severe itching. In cases of extensive involvement, shock symptoms may develop (headache, dizziness, nausea, bronchospasm, arterial hypotension, and tachycardia) or a complete state of shock may occur (Gaebelein-Wissing et al. 2020).

Fixed light urticaria: A specific form of light urticaria is fixed light urticaria. In this condition, wheals develop only in certain areas of the body. The rest of the skin remains free of symptoms even after exposure to light.

Delayed-type light urticaria: In this case, the local urticarial reaction does not occur within minutes, as is usually the case, but only after several hours.  

Associated conditions may include:

• Polymorphic light eruption
• Various forms of urticaria (heat, pressure, and cold urticaria)
• Churg-Strauss syndrome
• Stevens-Johnson syndrome
• Hypereosinophilic dermatitis

The clinical picture with the acute symptoms, the detection of wheals and the clear solar distribution pattern is diagnostic.

Acute urticaria of other genesis.

Cautious light-hardening may be attempted for patients who are able to schedule regular treatment sessions. Precise testing of the triggering spectrum, followed by determination of the individually appropriate light-hardening regimen.

• Positive results have been achieved with systemic PUVA therapy.
• Attempt rapid curing using UVA1.
• An alternative to PUVA therapy: narrowband UVB.

Antihistamines at the usual dosage are often insufficient. Higher dosages or combinations of various antihistamines are effective in milder cases. 

Glucocorticoids+antihistamines: In the initial phase, provide symptom-based emergency treatment as for acute urticaria: if necessary, high-dose systemic glucocorticoids (100–150 mg prednisolone equivalent) IV and antihistamines IV (e.g., Fenistil). In cases of shock symptoms , manage as for anaphylactic shock.

Alternatively: Chloroquine(Note: clinical effects are less than satisfactory)

Alternatively: Plasmapheresis can achieve a marked improvement in the clinical picture, particularly in patients with serum factor.

Alternative: Immunosuppressants—In severe cases, immunosuppressants (e.g., cyclosporine A) may be tried.

Alternative:IVIG: Improvement in symptoms has been reported following IVIG.

Alternative:Omalizumab: Experience with omalizumab, an IgE antibody, is increasingly positive. Its use is warranted in cases of treatment resistance (see Allergo J Int 2016:16). In patients weighing >100 kg, a higher dosage (450–600 mg every 4 weeks) may be effective. In cases of treatment resistance, the use of dupilumab (at the standard dose) may be effective (Navarro-Trivino FJ et al. 2023).      

The disease course ranges from months to years, with symptoms that are more bothersome than life-threatening. Remission may occur spontaneously after months or years (a course lasting 2–3 decades is possible). In larger studies, complete resolution of symptoms was demonstrated in 25% of patients within a 10-year period. Severe clinical symptoms accompanied by shock are rare.

Prescription of broad-spectrum sunscreens with a correspondingly high sun protection factor. Note: Basic sun protection measures are generally insufficient (Navarro-Trivino FJ et al. 2023). 

Long-term administration of antihistamines such as desloratadine (e.g., Aerius) 1 tablet per day or levocetirizine (e.g., Xusal) 1 tablet per day.

If necessary, try chloroquine (e.g.,^Resochin®); initial dose 250 mg/day orally, later 250 mg orally twice a week.

Detection of photodermatosis:

• Photoprovocation test on skin not exposed to the sun (buttocks, abdomen), since chronic exposure to light increases the urticaria threshold. According to the individual action spectrum, characteristic wheals are often triggered after the light staircase with UVA and UVB has been carried out. In some patients (in larger collectives this is about 15%) visible light (slide projector) can also be provoked.
• > 90% of patients can be provoked by UVA.
• In order to determine the exact action spectrum as well as the minimum quad dose ( MUD = minimum urticarial dose), additional irradiations of 250-700 nm with a monochromator are useful, if possible (but they are not available in clinical routine).
• Alternatively, cautious (controlled) irradiation with natural sunlight can be performed.
• The test reactions are read immediately and up to one hour after irradiation.
• Serum factor test (no longer relevant in practice): collection of patient serum and irradiation of the serum with 0.1 J/cm2 UVB, 10 J/cm2 UVA or with visible light (depending on the action spectrum determined) and subsequent intracutaneous injection of 0.05-0.1 ml serum and a control with 0.05-0.1 ml 0.9% NaCl-Lsg. After 5 and 15 minutes, assess whether a wheal forms at the injection site.

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