Differential Diagnosis for 7-year-old Male with Persistent Fever
Single Most Likely Diagnosis
- Southern Tick-Associated Rash Illness (STARI) or Ehrlichiosis: Given the tick exposure and the lack of response to doxycycline, which is typically effective against Lyme disease, these tick-borne illnesses are strong considerations. Ehrlichiosis, in particular, can cause persistent fever and may not respond immediately to doxycycline.
Other Likely Diagnoses
- Lyme Disease: Although doxycycline is the treatment of choice, the persistence of fever could indicate either a resistant strain or an additional infection. Lyme disease is a common tick-borne illness that can present with fever among other symptoms.
- Babesiosis: This is another tick-borne disease that can cause fever. It might not respond to doxycycline alone, as it often requires a combination of atovaquone and azithromycin for treatment.
- Anaplasmosis: Similar to Ehrlichiosis, Anaplasmosis is a tick-borne disease caused by Anaplasma phagocytophilum. It can present with fever, headache, and muscle pain, and while doxycycline is effective, the response may vary.
Do Not Miss Diagnoses
- Rocky Mountain Spotted Fever (RMSF): This is a potentially deadly tick-borne disease that requires prompt treatment. It can present with fever, headache, and rash, and the failure to respond to doxycycline could be due to a delay in treatment or a severe infection.
- Tularemia: Caused by Francisella tularensis, tularemia can be transmitted by ticks and can lead to severe disease if not treated promptly. It presents with fever, skin ulcers, and lymphadenopathy.
- Severe Bacterial Infections (e.g., Septicemia, Meningitis): Although less directly related to tick exposure, these conditions are life-threatening and require immediate diagnosis and treatment. The persistence of fever despite antibiotic treatment raises concerns about a more severe underlying infection.
Rare Diagnoses
- Tick-Borne Relapsing Fever (TBRF): Caused by various Borrelia species, TBRF is less common and can present with recurring episodes of fever. It's a consideration in endemic areas but is less likely given the initial presentation.
- Powassan Virus Disease: A rare but potentially severe tick-borne viral disease that can cause fever, headache, and encephalitis. Its rarity and the fact that it doesn't respond to doxycycline make it a less likely but important consideration.