Differential Diagnosis for the Patient's Condition

The patient's symptoms and history suggest a skin reaction to a plant encountered during her yoga retreat in Nicaragua. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Contact dermatitis (phytocontact dermatitis): This is the most likely diagnosis given the patient's history of brushing against a plant and the subsequent development of a skin imprint. The initial light red color that progressed to a dark red color, along with the fact that it is blanchable and does not hurt or itch, supports this diagnosis. Phytocontact dermatitis is a common reaction to certain plant allergens.

• Other Likely Diagnoses

  • Insect bite reaction: Although the patient mentions brushing against a plant, it's possible she was also bitten by an insect, which could cause a similar skin reaction. The lack of itching makes this less likely but does not rule it out entirely.
  • Irritant contact dermatitis: This could occur if the plant or another substance caused a non-allergic irritation to the skin. The persistence and color change could fit this diagnosis, although the lack of discomfort is somewhat atypical.

• Do Not Miss Diagnoses

  • Lyme disease: Although less common in Nicaragua compared to other parts of the world, Lyme disease can cause a distinctive "bull's-eye" rash (erythema migrans) that might initially be mistaken for a plant or insect bite reaction. It's crucial to consider this diagnosis due to its potential long-term consequences if left untreated.
  • Leishmaniasis: This is a parasitic disease spread by sandflies, which can cause skin lesions. Nicaragua is an endemic area for leishmaniasis, making this a critical diagnosis not to miss, especially given the patient's travel history.

• Rare Diagnoses

  • Phytophotodermatitis: This is a rare condition caused by contact with certain plant chemicals (like furanocoumarins in lime juice or certain weeds) followed by exposure to sunlight, leading to a phototoxic reaction. The reaction can cause blistering, burning, and long-lasting hyperpigmentation.
  • Rickettsial diseases: These are bacterial infections spread by ticks, mites, or fleas and can cause rash and fever. While less common, they are potentially severe and should be considered in travelers to endemic areas.

Recommended Actions

• The patient should be questioned further about her activities and exposures during the retreat.
• A thorough physical examination should be conducted to look for any other signs or symptoms that might suggest one of the less common diagnoses.
• Given the patient's travel history and the potential for serious diseases, a watchful waiting approach with follow-up appointments may be prudent, alongside education on signs of worsening or complications to look out for.
• Consideration should be given to empirical treatment for common causes (like contact dermatitis) while also keeping a low threshold for further diagnostic testing if the condition does not resolve or if new symptoms develop.