Differential Diagnosis for an 84-year-old with a Rash on the Face after Cutting in the Garden

• Single most likely diagnosis:
  • Contact dermatitis: This is likely due to exposure to allergens or irritants while gardening, such as plants, soil, or gardening tools.
• Other Likely diagnoses:
  • Photoallergic contact dermatitis: Similar to contact dermatitis but involves an allergic reaction to substances that become active upon exposure to sunlight.
  • Irritant contact dermatitis: Direct irritation from substances like pesticides, fertilizers, or certain plant sap.
  • Insect bites or stings: Could cause localized reactions that resemble a rash.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Lyme disease: Although less common, if the patient was exposed to ticks while gardening, Lyme disease could present with a rash (erythema migrans).
  • Phototoxicity: Certain medications can cause phototoxic reactions when exposed to sunlight, which could be exacerbated by gardening activities.
• Rare diagnoses:
  • Phytophotodermatitis: A rare condition caused by contact with certain plant chemicals and subsequent exposure to sunlight, leading to blistering and skin discoloration.
  • Allergic reactions to specific plants: Some plants can cause severe allergic reactions upon contact, though this is less common.