Pediatric Rocky Mountain Spotted Fever Differential Diagnoses

Updated: Apr 14, 2021
  • Author: Asif Noor, MD; Chief Editor: Russell W Steele, MD  more...
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DDx

Diagnostic Considerations

Rocky Mountain spotted fever (RMSF) is a life-threatening disease. Therefore, it is important to consider the possibility of RMSF in any patient whose clinical presentation is consistent with the disease. Clinicians should have a low threshold for treatment if RMSF is clinically suspected.

Signs and symptoms can mimic those of other diseases. Therefore, a history of traveling to endemic areas, having tick bites, or having exposures to ticks is an important clue. Absence of a history of tick bites should not exclude the diagnosis if the index of clinical suspicion is high.

The differential diagnosis of RMSF includes other infections with fever and rash, especially those involving rash including palms and soles, such as the following:

An enteroviral infection is typically seen in summer months, the child is relatively well-appearing, and the screening laboratory tests usually do not reveal significant derangements. In a sexually active individual, secondary syphilis can present with fevers and rash, including on the palms and soles. Invasive West Nile virus infection causes maculopapular rash with a petechial component. Sepsis, especially meningococcemia, should be considered in a toxic-appearing child who presents with fever and a purpuric rash. Toxin-mediated gram-negative sepsis should be considered in an immunocompromised host with fever and rash.

Other tick-borne infections, such as monocytic ehrlichiosis and granulocytic anaplasmosis, can present strikingly similarly to RMSF.  However, ehrlichiosis usually is associated with leucopenia; thrombocytopenia and rash are often absent. It should be kept in mind that tick-borne co-infections are possible in the same patient bitten by the same tick.

Other infectious and inflammatory entities that may have clinical features that can be confused with those of RMSF include the following:

  • Infectious mononucleosis
  • Parvovirus infection
  • Roseola
  • Scarlet fever
  • Leptospirosis
  • Kawasaki disease
  • Typhoid fever and dengue should be in the differential if the patient has a history of travel
  • The new Phlebovirus (Heartland virus) seen mostly in Missouri, and a new rickettsial species ( Rickettsia amblyommii) seen in North Carolina, may present similarly to infection with R rickettsii        
  • Fever and rash can also be present with noninfectious conditions, such as drug reactions, and vasculitis

Differential Diagnoses