Differential Diagnosis for Bullseye Rash
- Single most likely diagnosis
- Lyme disease: This is the most common cause of a bullseye 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 presents with a similar bullseye rash. However, it is not associated with the same long-term complications as Lyme disease.
- Tick-borne relapsing fever: This disease is caused by several species of Borrelia spirochetes and can present with a rash, although it is not always a bullseye pattern.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Rocky Mountain spotted fever: Although the rash in RMSF is typically petechial, it can sometimes appear as a bullseye pattern. RMSF is a life-threatening disease that requires prompt treatment.
- Tularemia: This bacterial infection can cause a skin ulcer or rash at the site of the tick bite, which may resemble a bullseye rash. Tularemia can be severe and even life-threatening if not treated promptly.
- Rare diagnoses
- African tick-bite fever: This disease is caused by Rickettsia africae and is typically acquired through the bite of an infected tick. It can present with a rash, including a bullseye pattern, although this is less common.
- Masters disease: This is a condition caused by the bite of an infected lone star tick, which can present with a bullseye rash similar to STARI. However, it is a rare condition and not well-studied.