Differential Diagnosis for Annular Lesion after Trauma in Mexico

Single most likely diagnosis

• Lyme disease: Although Lyme disease is more commonly associated with the United States, it can be found in Mexico. The annular lesion (erythema migrans) is a hallmark of early Lyme disease, which can cause pain and discomfort, including pain while walking if the lesion is located on the foot or lower extremity.

Other Likely diagnoses

• Cellulitis: A bacterial skin infection that can cause redness, swelling, and pain, especially after a traumatic injury. It might not typically present with an annular shape but could be considered given the context of trauma and pain.
• Eczema or contact dermatitis: Could be caused by exposure to an allergen or irritant in Mexico, presenting as an annular lesion. However, the direct link to trauma and the specific location might make this less likely.
• Dermatophyte infection (ringworm): A fungal infection that can cause annular lesions. It's common worldwide, including Mexico, and could be exacerbated by trauma or moisture.

Do Not Miss diagnoses

• Leishmaniasis: A parasitic disease prevalent in Mexico, transmitted by the bite of an infected sand fly. It can cause skin lesions that might appear annular and can be painful. Given the geographical location and the potential for severe consequences if left untreated, it's crucial not to miss this diagnosis.
• Rabies: Although rabies typically presents with neurological symptoms, the initial bite wound could potentially become infected or inflamed, causing pain. The history of being hit by something in Mexico raises concerns about potential animal bites.
• Tetanus: A bacterial infection caused by Clostridium tetani, which can enter the body through wounds. It's characterized by muscle stiffness and spasms, which could cause pain when walking. The risk of tetanus is higher in contaminated wounds.

Rare diagnoses

• Pinta: A tropical disease caused by Treponema carateum, characterized by skin lesions. It's rare and found in certain regions of Mexico and Central and South America. The lesions can be painful and might resemble annular lesions in their later stages.
• Yaws: Another treponemal infection that can cause skin lesions, although it's more common in children and in specific endemic areas. The primary lesion (mother yaw) can be painful and might be mistaken for an annular lesion.