Differential Diagnosis for the 4-year-old Boy with a Rash
- Single most likely diagnosis
- Impetigo: This is the most likely diagnosis due to the presence of small, round spots that developed into pustules, and the affected area appearing slightly moist with a transparent, yellow crusting. The rash is also mildly itchy and painful, which is consistent with impetigo. The fact that the patient's sister has also developed similar spots suggests a contagious etiology, which is also consistent with impetigo.
- Other Likely diagnoses
- Contact dermatitis: Given the patient's history of atopic dermatitis, contact dermatitis is a possible diagnosis. The rash is localized to one area, which could suggest exposure to an allergen or irritant.
- Folliculitis: The presence of pustules and papules on the foot could also suggest folliculitis, an inflammation of the hair follicles.
- Eczema herpeticum: Although less likely, eczema herpeticum is a possible diagnosis given the patient's history of atopic dermatitis. However, the lack of induration, streaking erythema, and systemic symptoms makes this diagnosis less likely.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Cellulitis: Although the patient does not have systemic symptoms or induration, cellulitis is a possible diagnosis that should not be missed. If left untreated, cellulitis can lead to serious complications, including sepsis.
- Necrotizing fasciitis: This is a rare but life-threatening condition that can present with a similar rash. Although the patient's symptoms are mild, necrotizing fasciitis should be considered in the differential diagnosis.
- Rare diagnoses
- Pitted keratolysis: This is a rare condition that causes small, round spots on the feet. However, it is typically associated with hyperhidrosis and does not usually present with pustules or crusting.
- Dyshidrotic eczema: This is a rare condition that causes small, round spots on the hands and feet. However, it is typically associated with intense itching and does not usually present with pustules or crusting.