A 45-year-old farmer has itchy erythematous papular lesions on face, neck, 'V' area of chest, dorsum of hands and forearms for 3 years. The lesions are more severe in summers and improve by 750/a in winters. The most appropriate test to diagnose the condition would be:
High-Yield Explanation
A i.e. Skin biopsy - Presence of itchy papules or papulovesicles on sun-exposed areas paicularly! of forearm with a history of seasonal variations ie more severe in summer and improved in wintersQ - for long duration suggest the diagnosis of - Polymorphic light reaction. Diagnosis of PLR is confirmed by skin biopsy and by performing photo-test procedures (i.e. photo-patch test & photo provocative tests)Q. Phototoxicity - is a non-immunological reaction caused by photo toxic drugs - amiodarone, dacarbazine, fluroquinolones, 5-FU, furosemide, nalidixic acid, phenothiazines, psoralens, retinoids, sulfonamides, sulfonylureas, tetracyclines, thiazides, vinblastin. The usual clinical manifestations include erythema resembling a sunburn reaction that quickly desquamates, or "peels", within several days. In addition, edema, vesicles and bullae may occur. Photo allergy - is immune mediated, less common reaction caused by - 6-methyl-coumarin, aminobenzoic acid and esters, bithionol, chlorpromazine, diclofenac, fluroquinolones, halogenated salicylanilides, hypericin (st John's Wo), Musk ambrette, piroxicam, promethazine, Sulfonamides and Sulfonylureas. The clinical manifestations typically differs from those of phototoxicity in that an intensely pruritic eczematous dermatitis tends to predominate and evolves into lichenified, thickened, "leathery" changes in sun exposed areas. A small subset of patients (5-10%) may develop a persistent equisite hypersensitivity to light even when the offending drug or chemical is identified and eliminated, a condition known as persistent light reaction. - A very uncommon type of persistent photosensitivity is known as chronic actinic dermatitis. These patients are typically elderly men with a long history of preexisting allergic contact dermatitis or photosensitivity. They are usually exquisitely sensitive to UV-B, UV-A and visible wave lengths (ie manifest a broad spectrum of UV - hyperresponsiveness). - Diagnostic confirmation of phototoxicity & photoallergy can be done by using photo test procedures. For phototoxicity & photoallergy UV-A radiation (MED = minimal erythema dose) is used. Patients with persistent light reaction characteristically show diminished threshold to erythema evoked by UV -B. In solar uicaria, lesions occur within minutes of sun exposure, on exposed areas.