Prevalence and predictors of low vitamin D status in patients referred to a tertiary photodiagnostic service: a retrospective study.

BACKGROUND/PURPOSE: Low vitamin D levels have been associated with adverse effects on health. The primary source of vitamin D is cutaneous production during sunlight exposure. Sun avoidance can restrict vitamin D photosynthesis and is common practice amongst patients with photosensitivity. Few studies have examined vitamin D status in this population, particularly those in northern latitudes. The purpose of this study was therefore to investigate the prevalence and possible predictors of low vitamin D status in patients referred to a tertiary photodiagnostic service. METHODS: A case note review of 165 patients who attended the National Photodiagnostic Service for assessment at the Photobiology Unit in Dundee, Scotland (latitude 56 °N) over 1 year was conducted. Clinical information and serum 25-hydroxyvitamin D (25(OH)D) concentration were documented. Multivariate analyses were used to identify predictors of vitamin D status. RESULTS: Mean 25(OH)D concentration was 41.9 nmol/L [standard deviation (SD) 22.0]. Forty percent of patients had insufficient vitamin D levels [25(OH)D 25-49 nmol/L] and 25% were vitamin D deficient [25(OH)D<25 nmol/L]. Blood collection in winter was the strongest predictor of low 25(OH)D status (P<0.001); strict photoprotection (P=0.04), onset of symptoms within an hour of sunlight exposure (P=0.01) and abnormal monochromator phototesting responses (P=0.009) also predicted low vitamin D levels. Supplement use was associated with higher vitamin D levels (P<0.001), even amongst patients who strictly avoided sunlight (P=0.03). CONCLUSIONS: Patients with photosensitivity who live in northern latitudes are at high risk of low vitamin D levels, particularly in winter and spring. Increased awareness of this risk is crucial to ensure preventative strategies, such as supplementation, are implemented.

Localized bullous pemphigoid induced by photodynamic therapy.

Topical photodynamic therapy (PDT) causes localized phototoxicity and has been shown both in vitro and in humans to have immunomodulatory and immunosuppressive effects. We report a case of localized bullous pemphigoid (BP) developing after PDT. Although BP has been reported to develop following cutaneous insults such as surgery, radiotherapy, psoralen ultraviolet A (PUVA) and ultraviolet B phototherapy, PDT has not previously been reported as a trigger. Possible mechanisms include direct mechanical injury to the basement membrane and subsequent autoantibody formation, an indirect immunomodulatory effect of PDT, or most likely, precipitation of BP in individuals with pre-existing low titres of epidermal autoantibodies (so-called subclinical BP). PDT should be added to the list of possible exogenous triggers for BP and this condition should be considered if blistering develops following PDT.

A double-blind, randomized assessment of the irritant potential of sunscreen chemical dilutions used in photopatch testing.

BACKGROUND: The maximum concentration of organic sunscreen filters in current usage that does not lead to irritant reactions when performing photopatch testing is not known. Such irritant reactions can be misinterpreted as positive photoallergic contact dermatitis reactions. OBJECTIVE: To determine the frequency of irritant reactions to 19 organic sunscreen filters in current use. PATIENTS/METHODS: Ninety-four healthy volunteers were photopatch tested using the European consensus methodology to three different concentrations (2%, 5%, and 10%) of 19 organic sunscreen filters at the Photobiology Unit in Dundee, UK. RESULTS: Of the 94 subjects recruited, 80 were analysed after withdrawals and exclusions. Of the 19 organic sunscreen filters studied, only 2 compounds led to irritant reactions in > or =5% subjects. Five per cent and 10% benzophenone-4 led to irritant reactions in four and six subjects, respectively. Five per cent methylene bis-benzotriazolyl tetramethylbutylphenol led to irritant reactions in six subjects, but unlike benzophenone-4, this was not in a dose-dependent fashion. CONCLUSIONS: When performing photopatch testing according to the European consensus methodology with these 19 organic sunscreen filters, a 10% concentration is suitable for all filters, except benzophenone-4, which should be tested at a concentration of 2%.