Differential Diagnosis for Elevated Monocyte and Tick Illness

• Single most likely diagnosis
  • Ehrlichiosis: This diagnosis is likely due to the combination of elevated monocytes and a history of tick illness. Ehrlichiosis is a tick-borne disease caused by the Ehrlichia bacterium, which can lead to an increase in monocytes.
• Other Likely diagnoses
  • Anaplasmosis: Similar to Ehrlichiosis, Anaplasmosis is a tick-borne disease that can cause an increase in monocytes. It is caused by the Anaplasma bacterium and has similar symptoms to Ehrlichiosis.
  • Lyme disease: Although Lyme disease is more commonly associated with an increase in lymphocytes, some cases can present with an increase in monocytes. It is a tick-borne disease caused by the Borrelia burgdorferi bacterium.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Rocky Mountain Spotted Fever (RMSF): This is a tick-borne disease caused by the Rickettsia rickettsii bacterium. Although it may not be as likely as other diagnoses, RMSF can be deadly if left untreated, making it a crucial diagnosis not to miss.
  • Southern Tick-Associated Rash Illness (STARI): Although not typically associated with elevated monocytes, STARI can present with a rash and other symptoms similar to those of tick-borne illnesses. It is essential to consider this diagnosis to rule out other potentially deadly conditions.
• Rare diagnoses
  • Tularemia: This is a rare tick-borne disease caused by the Francisella tularensis bacterium. It can present with an increase in monocytes, but it is less common than other tick-borne illnesses.
  • Babesiosis: This is a rare tick-borne disease caused by the Babesia parasite. It primarily affects red blood cells but can also lead to an increase in monocytes in some cases.