Differential Diagnosis for a Bump in the Area of a Tick Bite

• Single most likely diagnosis:
  • Lyme disease: This is the most common tick-borne illness, and a bump or rash at the site of the tick bite is a hallmark symptom. The rash, known as erythema migrans, typically appears within a week of the bite.
• Other Likely diagnoses:
  • Southern tick-associated rash illness (STARI): This condition, also known as Masters disease, presents with a rash similar to that of Lyme disease but is caused by a different tick-borne pathogen.
  • Tick bite granuloma: A localized reaction to the tick bite can cause a bump or nodule at the bite site, which may resemble an insect bite reaction.
• Do Not Miss diagnoses:
  • Rocky Mountain spotted fever (RMSF): Although less common, RMSF is a serious and potentially life-threatening tick-borne disease that can present with a rash, including at the site of the tick bite.
  • Anaplasmosis: Another tick-borne disease that can cause fever, headache, and rash, anaplasmosis requires prompt treatment to prevent serious complications.
  • Ehrlichiosis: Similar to anaplasmosis, ehrlichiosis is a tick-borne bacterial infection that can cause severe illness if not treated promptly.
• Rare diagnoses:
  • Babesiosis: A parasitic disease transmitted by ticks, babesiosis can cause a range of symptoms, including fever, chills, and anemia, but is less commonly associated with a localized bump at the bite site.
  • Tularemia: Also known as rabbit fever, tularemia is a rare tick-borne bacterial infection that can cause skin ulcers, among other symptoms, but is less likely to present as a simple bump at the bite site.