What you need to know about Photodermatoses
Most public health messages have focused on the hazards of too much sun exposure. However, excessive UVR (ultraviolet radiation) exposure accounts for only 0.1 percent of the total global burden of disease. The same WHO (World Health Organization) report notes that a markedly larger annual disease burden of 3.3 billion results from very low levels of UVR exposure. This burden includes major disorders of the musculoskeletal system. In addition to building bones and keeping them healthy, calcium enables our blood to clot, our muscles to contract, and our heart to beat. About 99 percent of calcium is in our bones and teeth. Calcium and vitamin D are essential to building strong dense bones when one is young and keeping them strong and healthy as one ages. Vitamin D plays an important role in protecting your bones, as it helps the body to absorb calcium and supports the muscles to avoid accidental falls. If you don’t get enough vitamin D, you’re more likely to break bones as you age and possibly suffer an increased risk of various autoimmune diseases and life-threatening cancers (colorectal CA, breast CA, prostate cancer and Non Hodgkin’s Lymphoma {NHL}). On the other hand, exposure to both UVA and UVB radiation can have direct immunosuppressive effects through upregulation of cytokines (chemical inflammatory mediators) and increased activity of T regulatory cells that remove self-reactive T cells. Regulatory T cells are known to be lacking in some patients with autoimmune diseases. Previous research has also shown that regulatory T cell function is enhanced by vitamin D. These mechanisms may help prevent autoimmune diseases like multiple sclerosis.
Photodermatoses can be quite common especially in tropical countries like the Philippines. These skin disorders are precipitated by exposure to sunlight and exacerbated by light but are different from acute reactions such as sunburn. Sunburn and photoaging can occur in anyone exposed to sufficiently high levels of UV radiation. Conversely, photodermatoses are abnormal reactions to UV light even at low levels only and do not affect everyone but instead are triggered by sun or light exposure in some individuals. Photodermatoses are most commonly triggered by UVA radiation (320-400 nm). Skin eruptions occur during or soon after exposure to sunlight or artificial light radiation on exposed areas of the skin. The most common photodermatosis worldwide is polymorphous light eruption. Photoaggravated dermatoses and drug-induced photosensitivity are also not uncommon; however, other types of photodermatoses are rather rare.
General approach to diagnosis
Given that the clinical features of photodermatoses vary widely, diagnosis can be challenging. Suspicion should be aroused when skin eruptions occur in UV-exposed sites after sun exposure. It is important to conduct a systematic evaluation, including an assessment of the patient’s history, as well as photodiagnostic procedures. The lists below should be gathered and evaluated when determining a photodermatosis diagnosis. Understanding the relationship between sun exposure and the appearance of skin abnormalities is key. Knowing which photodermatoses are most common in the various age groups can also help to narrow the diagnosis. As noted by Bylaite et al, “An itchy rash can appear within minutes, as in solar urticaria, and resolve within an hour or develop a few hours or days later after light exposure, as in polymorphous light eruption.”
When assessing someone with a possible photodermatosis, a full history is important, which mostly includes: age of onset; timing of the rash after sun exposure (interval between sun exposure and subsequent skin eruptions); seasonal differences; type of discomfort or pain (e.g. itching or severe burning compared with an atypical case of sunburn); how much exposure is required to trigger symptoms; whether it still occurs despite protection with sun cream and/or whether it is blocked by glass (which blocks ultraviolet rays).
Also, it is important to take a full medication history, including topical skin applications and drugs such as NSAIDS, diuretics, food additives, which are not always considered as drugs by patients. Also whether there has been use of perfumes or contact with airborne sensitizers or plants. Also important is any past history or significant family history as well as any systemic symptoms and history of any connective tissue disease.
Since these vital bits of information are necessary to come up with the correct diagnosis, a visit to a dermatologist is of utmost importance.
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