Differential Diagnosis for Scarring Rash in a 3-year-old

Single Most Likely Diagnosis

• Impetigo: This is a common bacterial skin infection in children, often caused by Staphylococcus aureus or Streptococcus pyogenes, which can lead to scarring if not properly treated. The presence of a scarring rash in a 3-year-old, especially if accompanied by signs of infection like pus or crusting, makes impetigo a leading consideration.

Other Likely Diagnoses

• Eczema (Atopic Dermatitis) with Secondary Infection: While eczema itself typically does not cause scarring, repeated scratching and secondary bacterial infections can lead to scarring lesions. The history of atopic dermatitis and signs of infection would support this diagnosis.
• Chickenpox (Varicella): Although chickenpox is usually associated with a non-scarring rash, in some cases, especially if the lesions become secondarily infected, scarring can occur. The presence of a rash in various stages of healing and a history of exposure would be key factors.
• Insect Bites with Secondary Infection: Similar to eczema, insect bites themselves are unlikely to cause scarring but can if they become infected and are repeatedly scratched.

Do Not Miss Diagnoses

• Meningococcemia: This is a severe infection caused by Neisseria meningitidis, which can present with a rash that may initially appear as non-specific but can evolve into a petechial or purpuric rash, potentially leading to scarring. The rapid progression and severity of the illness, along with signs of sepsis, make this a critical diagnosis not to miss.
• Staphylococcal Scalded Skin Syndrome (SSSS): Caused by staphylococcal toxins, SSSS can lead to widespread skin exfoliation and, in severe cases, scarring. The presence of fever, skin tenderness, and the characteristic appearance of the skin would suggest this diagnosis.

Rare Diagnoses

• Epidermolysis Bullosa: A group of genetic conditions that result in blistering of the skin and mucous membranes, which can lead to scarring. The presence of blisters and erosions, especially after minor trauma, and a family history would support this diagnosis.
• Sarcoidosis: A condition that can cause skin lesions, among other systemic symptoms. While rare in children, it could present with a scarring rash, especially if accompanied by other systemic signs like lymphadenopathy or respiratory symptoms.