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What is 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 75% in winters. The most appropriate test to diagnose the condition would be: and explain in detail?
Patient in the question is showing features of chronic allergic contact dermatitis, as indicated by the clinical manifestations in exposed areas of the body and its exacerbation during summer season. Patch testing is done to document sensitivity to a specific antigen. In this procedure, a battery of suspected allergens is applied to the patient's back under occlusive dressings and allowed to remain in contact with the skin for 48 hrs. After removal of the dressings the area is examined for evidence of delayed hypersensitivity reactions (e.g., erythema, edema, or papulo vesicles). Ref: CURRENT Medical Diagnosis and Treatment, 2012, Chapter 6; Harrison's Principles of Internal Medicine, 18h Edition, Chapter 51.