Differential Diagnosis for a 6-year-old with a Pruritic Papular Vesicular Rash on 1 Foot

• Single most likely diagnosis:
  • Dyshidrotic eczema (Pompholyx): This condition is characterized by small, itchy blisters on the hands or feet, often associated with atopic dermatitis. The unilateral presentation and the specific location on one foot make this a strong consideration.
• Other Likely diagnoses:
  • Contact dermatitis: An allergic reaction or irritation from substances like soap, detergent, or certain plants could cause a pruritic papular vesicular rash, especially if the child has been playing outdoors or has been exposed to new substances.
  • Scabies: Although scabies typically presents with a more widespread rash, it can start with a localized area, especially in children. The intense itching and possibility of vesicles make it a plausible diagnosis.
  • Insect bites or stings: Reactions to insect bites can cause pruritic papules or vesicles and are common in children who spend time outdoors.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Cellulitis: While less likely to present with vesicles, cellulitis is a serious bacterial infection of the skin that requires prompt antibiotic treatment. It can start with redness, swelling, and warmth in one area, which might initially resemble a rash.
  • Erythema multiforme: A skin condition characterized by target lesions, which can sometimes appear as vesicles. It can be associated with infections or medications and, in rare cases, can be a sign of a more serious condition.
• Rare diagnoses:
  • Pustular psoriasis: Although rare in children, pustular psoriasis can present with vesicles or pustules on the skin, often accompanied by erythema and scaling.
  • Keratolysis exfoliativa (dyshidrosis lamellosa sicca): A condition that causes the skin on the palms or soles to peel, sometimes preceded by vesicles. It's less common and might be considered if other diagnoses are ruled out.