Differential Diagnosis of Scarlet Fever

The differential diagnosis of scarlet fever, a condition characterized by a distinctive rash and typically caused by Group A beta-hemolytic streptococci (GABHS), includes a range of other infectious and non-infectious conditions. Here's a categorized approach to the differential diagnosis:

• Single Most Likely Diagnosis

  • Kawasaki Disease: This condition, primarily affecting children, presents with fever, rash, mucous membrane changes, and lymphadenopathy, overlapping significantly with the symptoms of scarlet fever. The diagnosis is clinical, and distinguishing it from scarlet fever can be challenging without specific diagnostic criteria.

• Other Likely Diagnoses

  • Toxic Shock Syndrome (TSS): Caused by bacterial toxins, TSS can present with fever, rash, and hypotension. While the rash in TSS is more likely to be diffuse and macular, it can sometimes be confused with the rash of scarlet fever.
  • Measles: Although vaccination has made measles less common, it remains a consideration in the differential diagnosis of scarlet fever, especially in unvaccinated populations. Measles presents with fever, cough, coryza, conjunctivitis, and a characteristic rash.
  • Rubella (German Measles): Similar to measles, rubella is less common due to vaccination but can present with a rash and fever, making it a differential diagnosis for scarlet fever.
  • Infectious Mononucleosis: Caused by Epstein-Barr virus (EBV), infectious mononucleosis can sometimes present with a rash, particularly if the patient is taking ampicillin, which can induce a rash in patients with EBV infection.

• Do Not Miss Diagnoses

  • Staphylococcal Scalded Skin Syndrome (SSSS): This condition, caused by staphylococcal toxins, presents with fever, rash, and skin exfoliation. It is particularly dangerous in neonates and young children and requires prompt recognition and treatment.
  • Meningococcemia: This severe infection, caused by Neisseria meningitidis, can present with fever, rash, and shock. The rash can be petechial or purpuric and is a medical emergency.
  • Rocky Mountain Spotted Fever (RMSF): Caused by Rickettsia rickettsii, RMSF presents with fever, headache, and a characteristic rash. It is a tick-borne illness that can be fatal if not treated promptly.

• Rare Diagnoses

  • Erythema Infectiosum (Fifth Disease): Caused by parvovirus B19, this condition presents with a distinctive "slapped cheek" appearance and a lacy rash on the body. It is typically mild but can be a consideration in the differential diagnosis of scarlet fever.
  • Enteroviral Infections: Certain enteroviruses can cause rashes and fever, making them rare but possible differential diagnoses for scarlet fever.