Patients who have experienced solar urticarial symptoms from a young age could mistakenly be thought to have erythropoietic protoporphyria. However, the main symptom for this disease is pain and patients with have been found to have abnormal levels of protoporphyrin in their blood while these levels are normal in SU patients. Finally, cholinergic urticaria, or urticaria induced by heat, can occasionally appear to be solar urticaria because the heat from the sun will cause a person with the disease to have a reaction. Management
Antihistamines
Histamines are proteins associated with many allergic reactions. When the UV radiation or light comes in contact with a person with solar urticaria, histamine is released from mast cells. When this occurs, the permeability of vessels near the area of histamine release is increased. This allows blood fluid to enter the vessels and cause inflammation. Antihistamines suppress the activity of the histamine.Diphenhydramine, a first-generation H1 receptor antagonist or medicine that combats the H1 receptor that is associated with many allergic reactions, has been found to be the most potent antihistamine for this particular disease. Patients prescribed 50 milligrams four times per day have been able to sustain normal exposure to the sun without developing a reaction. Patients with less potent forms of solar urticaria such as fixed solar urticaria can be treated with the medication fexofenadine, which may also be used prophylactically to prevent recurrence.
The wavelength range of type III and IV spans from 400 to 500 nm, while type V can be caused by UVB radiation to visible light (280–600 nm). Type VI has only been known to occur at 400 nm.Another classification distinguishes two types. The first is a hypersensitivity caused by a reaction to photoallergens located only in people with SU; while the second is caused by photoallergens that can be found in both people with SU and people without it.A subgroup of solar urticaria, fixed solar urticaria, has also been identified. It is a rare, less intense form of the disease with wheals (swollen areas of the skin) that affect certain, fixed areas of the body. Fixed solar urticaria is induced by a broad spectrum of radiative energy with wavelengths ranging from 300 to 700 nm. Differential diagnosis
Polymorphous light eruption (PMLE) is the easiest disease to mistake for solar urticaria because the locations of the lesions are similar (the V of the neck and the arms). However, patients with SU are more likely to develop lesions on the face. Also, a reaction with PMLE will take a greater amount of time to appear than with solar urticaria. Lupus erythematosus has been mistaken for SU; however, lesions from lupus erythematosus will take a longer amount of time to go away. Furthermore, when being tested for the two diseases, patients with SU have a reaction immediately while patients with lupus erythematosus will have a delayed reaction.