Differential Diagnosis for Insect Bite with Scaling in a Circle

• Single most likely diagnosis
  • Tinea corporis (Ringworm): This is a fungal infection that can be triggered by an insect bite, leading to a circular lesion with scaling. The appearance of a ring-shaped lesion with scaling is highly suggestive of this diagnosis.
• Other Likely diagnoses
  • Erythema annulare centrifugum: An inflammatory condition that can cause ring-shaped lesions, which might be triggered by an insect bite. It presents with erythematous, annular (ring-shaped) plaques.
  • Granuloma annulare: A benign skin condition characterized by small, circular bumps that can appear as a ring. While not typically caused by an insect bite, it could be considered in the differential due to its appearance.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Lyme disease (Erythema migrans): Caused by the bite of an infected tick, it can present with a characteristic "bull's-eye" rash, which is a circular expanding lesion. Early diagnosis and treatment are crucial to prevent long-term complications.
  • Leishmaniasis: A parasitic disease spread by sandflies, which can cause skin lesions that might resemble a circular, scaling rash. It's essential to consider this in travelers to endemic areas.
• Rare diagnoses
  • Erythema chronicum migrans (without Lyme disease context): Though similar to erythema migrans, this condition is not associated with Lyme disease and presents with a migrating, annular erythema.
  • Subcutaneous mycoses (e.g., Sporotrichosis): Fungal infections that can cause skin lesions, which might appear as circular and scaling, especially if acquired through a skin prick or cut from a contaminated source like an insect bite.