A 50-year-old Thai female presents to the clinic with a markedly pruritic and burning rash on both legs that has persisted for 2 days.

• She worked as a food vendor and began using Kaffir lime on her legs as a preventative measure against mosquito bites, applying it directly to her skin while exposed to bright sunlight.
• Upon returning home, she noticed her legs were red, itchy, painful, and warm, with the symptoms confined to the areas that were exposed to the sun.
• The following day, she repeated the same Kaffir lime application, leading to an exacerbation of her symptoms, prompting her visit to the clinic for evaluation and treatment.

Question

What is the provisional diagnosis of this skin condition?

โดย ร.อ.ยุทธรัตน์ สุวรรณชาติกุล อาจารย์หน่วยตจวิทยา กองตรวจโรคผู้ป่วยนอก

รพ.ภูมิพลอดุลยเดช กรมแพทย์ทหารอากาศ

ANSWERs

"Phytophotodermatitis"

• Phytophotodermatitis frequently occurs in regions with high sun exposure and plant diversity, affecting people who come into contact with both plants and sunlight.
• This condition arises from a reaction between plant-derived chemicals (like psoralens, kaffir lime) and ultraviolet light, causing inflammation and skin damage.
• Common among vacationers, agricultural workers, children, and gardeners who unintentionally come into contact with photosensitizing plants while exposed to sunlight.
• Characterized by painful, erythematous streaks and patches that appear a day or more after exposure, often with delayed onset of rashes.
• A detailed patient history is crucial for identifying phytophotodermatitis, supported by laboratory tests if necessary to rule out other conditions.
• Unlike phytophotodermatitis, allergic phytodermatitis results from an immune response to plant substances, often presenting as pruritic, eczematous rashes with a history of prior exposure.
• Management: Addressing anxiety, using cool compresses, NSAIDs, topical emollients, and corticosteroids can help manage symptoms, though the condition usually resolves on its own with potential for hyperpigmentation. 

Reference:  Keah S, Chng K. A chinese new year rash. Malays. Fam. Physician. 2013;8:62–4.

โดย ร.อ.ยุทธรัตน์ สุวรรณชาติกุล อาจารย์หน่วยตจวิทยา กองตรวจโรคผู้ป่วยนอก

รพ.ภูมิพลอดุลยเดช กรมแพทย์ทหารอากาศ