Differential Diagnosis for 29yoM with Pruritic Nodules on Bilateral Legs Following Hiking

• Single Most Likely Diagnosis
  • Insect Bites or Stings: This is the most likely diagnosis given the history of hiking and the presence of pruritic nodules on the legs. Insect bites or stings can cause localized reactions that present as pruritic nodules.
• Other Likely Diagnoses
  • Contact Dermatitis: This could be due to exposure to plants like poison ivy, oak, or sumac during hiking. The pruritic nature of the nodules and their appearance after outdoor activity support this diagnosis.
  • Folliculitis: This is an inflammation of the hair follicles and can be caused by friction, sweat, or bacterial infection, all of which could be exacerbated by hiking.
  • Cutaneous Larva Migrans: This condition, caused by the larvae of hookworms, can result from walking barefoot or in contact with contaminated soil, leading to pruritic skin lesions.
• Do Not Miss Diagnoses
  • Lyme Disease: Although less common, Lyme disease, transmitted by tick bites, can initially present with a solitary lesion (erythema migrans) that may be pruritic. Given the potential severity of untreated Lyme disease, it's crucial not to miss this diagnosis.
  • Leishmaniasis: This parasitic infection, spread by sandflies, can cause skin lesions that are often pruritic. Although rare in many areas, it's a critical diagnosis to consider due to its potential for serious complications.
• Rare Diagnoses
  • Erythema Nodosum: A type of skin inflammation that can cause nodules, typically on the legs. It can be triggered by various factors, including infections and medications, but is less likely given the context.
  • Pernio (Chilblains): A condition caused by prolonged exposure to cold, damp environments, leading to inflammation of small blood vessels. While it can cause lesions on the legs, it's less likely to be pruritic and directly linked to hiking unless in very cold conditions.
  • Onchocerciasis (River Blindness): Caused by a parasitic worm transmitted through blackfly bites, it can lead to severe skin and eye lesions. However, it's extremely rare outside of specific endemic areas and would be an unlikely diagnosis without significant travel history to those regions.