Evaluation of the Patient with Photosensitivity

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Photosensitivity encompasses a range of conditions characterised by altered sensitivity to solar ultraviolet (UV) and/or visible radiation. Photosensitivity disorders can be divided into four broad categories: (i) idiopathic/immune-based dermatoses; (ii) drug and chemically induced reactions, including exogenously mediated reactions and the cutaneous porphyrias; (iii) disorders associated with defects in DNA excision repair; (iv) photoaggravated dermatoses, a wide range of disorders that may be worsened by light exposure. Photosensitive individuals develop abnormal skin reactions following sunlight exposure, and these can be replicated by exposure to artificial light sources in the laboratory. Characterisation of the photosensitive patient includes clinical evaluation with detailed history including details of symptoms of onset and current medication. Phototesting, i.e. assessment of skin responses following application of defined wavelengths and doses of UVB, UVA and visible radiation provides information on the action spectrum of the disorder and permits clinical assessment of rash morphology. Associated tests including autoantibody screening, porphyrin fluorescence scanning and histocompatability locus antigen subtyping further assist in diagnosis.