What is the most appropriate initial diagnostic study for a gardener with recurrent skin issues on his hand?

The most appropriate initial diagnostic study for a gardener experiencing recurrent skin issues on his hand is patch testing. This type of testing is specifically designed to identify allergic contact dermatitis, which is common among individuals who work with various plants, soil, and gardening chemicals. Gardeners are often exposed to a variety of allergens, including plant materials, pesticides, and fertilizers, all of which can lead to localized skin reactions.

Patch testing involves applying small amounts of various allergens to the skin and monitoring for reactions. This test is particularly useful for diagnosing contact allergies, allowing the practitioner to pinpoint specific substances that may be causing the dermatitis. Given the gardener's occupation and the likely environmental exposure to numerous potential allergens, patch testing can help establish a clear diagnosis and guide future avoidance strategies.

While skin scraping and microscopy may be useful for diagnosing infections like tinea, this scenario seems more aligned with a contact dermatitis. RAST testing, a blood test for allergies, is less common for contact allergens as it primarily assesses for systemic or immediate-type hypersensitivities rather than localized reactions. Skin biopsy, while valuable for evaluating various dermatoses and ruling out conditions like psoriasis or eczema, would be a secondary step after other less invasive tests if the patch test does not yield conclusive results.