Differential Diagnosis for a 9-year-old with Red Bullseye Rash, Lethargy, and Low-grade Fever
- Single most likely diagnosis:
- Lyme disease: This is the most likely diagnosis due to the characteristic "bullseye" rash (erythema migrans), which is a hallmark of early Lyme disease. The rash, combined with systemic symptoms like lethargy and low-grade fever, strongly suggests this diagnosis.
- Other Likely diagnoses:
- Southern tick-associated rash illness (STARI): This condition presents with a similar rash to Lyme disease but is caused by a different tick-borne illness. It's less common than Lyme but should be considered, especially in regions where the Lone Star tick is prevalent.
- Rocky Mountain spotted fever (RMSF): Although RMSF typically presents with a petechial rash rather than a bullseye rash, it can sometimes appear as a maculopapular rash. The presence of fever and lethargy, along with exposure to ticks, makes this a plausible diagnosis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
- Tick-borne relapsing fever: This rare condition, caused by various Borrelia species, can present with fever, rash, and systemic symptoms. It's crucial to consider due to its potential severity and the need for prompt antibiotic treatment.
- Ehrlichiosis/Anaplasmosis: These tick-borne diseases can cause severe systemic illness, including fever, lethargy, and sometimes rash. They are less common but can be life-threatening if not treated promptly.
- Rare diagnoses:
- Tularemia: Caused by Francisella tularensis, this bacterial infection can be transmitted by ticks and may present with a skin ulcer or rash, along with systemic symptoms like fever and lethargy. It's rare but should be considered in endemic areas or with specific exposures.
- Babesiosis: A parasitic infection transmitted by ticks, babesiosis can cause fever, lethargy, and sometimes rash, although it more commonly presents with hemolytic anemia. It's rare and typically seen in specific geographic areas or in individuals with certain risk factors.