Differential Diagnosis for Bulls Eye Rash

• Single most likely diagnosis
  • Lyme disease: This is the most common cause of a bulls eye rash, also known as erythema migrans. It is a characteristic skin lesion that appears in the early stage of Lyme disease, typically within 3-30 days after a tick bite.
• Other Likely diagnoses
  • Southern tick-associated rash illness (STARI): This condition is caused by the bite of the lone star tick and can also present with a bulls eye rash, although it is less common than Lyme disease.
  • Erythema multiforme: This is an immune-mediated condition that can cause a target-like rash, although it is not typically associated with a tick bite.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Rocky Mountain spotted fever: This is a tick-borne illness that can cause a rash, although it is not typically a bulls eye rash. However, it is a life-threatening condition if left untreated, so it is essential to consider it in the differential diagnosis.
  • Tularemia: This is another tick-borne illness that can cause a rash, as well as other systemic symptoms. It is a rare but potentially deadly condition if not treated promptly.
• Rare diagnoses
  • Tick-borne relapsing fever: This is a rare condition caused by the bite of an infected tick, which can cause a rash, as well as other symptoms such as fever and headache.
  • African tick-bite fever: This is a rare condition caused by the bite of an infected tick, which can cause a rash, as well as other symptoms such as fever and headache. It is typically seen in travelers to sub-Saharan Africa.