Differential Diagnosis of Buttock Rash in a 3-Month-Old Infant
The most likely diagnosis in a 3-month-old with buttock rash is irritant contact diaper dermatitis, followed by candidal diaper dermatitis, seborrheic dermatitis, and atopic dermatitis. 1, 2
Primary Differential Diagnoses
Irritant Contact Diaper Dermatitis (Most Common)
- Presents as erythema and irritation in the diaper area with sparing of skin folds 1, 2
- Caused by prolonged contact with urine and feces, which damages the skin barrier 1
- Peak incidence occurs between 9-12 months, but can occur at any age in the diaper period 1
Candidal Diaper Dermatitis
- Characterized by beefy red erythema with satellite papules and pustules, typically involving the skin folds 2
- Secondary infection with Candida albicans often complicates irritant diaper dermatitis 2
- Requires topical antifungal treatment rather than barrier creams alone 2
Seborrheic Dermatitis
- Presents as greasy, yellowish scaling that can extend from the scalp to the diaper area 3, 2
- In the diaper region, appears as well-demarcated erythematous patches with fine scale 2
- Distinguished from atopic dermatitis by lack of significant pruritus and typical distribution pattern 2
Atopic Dermatitis
- Less common in the diaper area at 3 months, but can present as erythematous, pruritic patches 4, 2
- Diagnosis requires itchy skin condition plus three or more criteria: history of skin crease involvement, history of atopy, general dry skin, visible flexural eczema, or early onset 4
- In infants under 4 years, commonly affects cheeks or forehead rather than buttocks 4
Important Conditions to Exclude
Eczema Herpeticum (Medical Emergency)
- Look for multiple uniform "punched-out" erosions or vesiculopustular eruptions that are very similar in shape and size 5
- Requires immediate systemic acyclovir as it "may progress rapidly to systemic infection in the absence of antiviral therapy" 5
- Consider if there are grouped vesicles or rapid progression 5
Secondary Bacterial Infection
- Suspect if there is crusting, weeping, or honey-colored discharge 6, 4
- Flucloxacillin is the most appropriate antibiotic for treating Staphylococcus aureus 4
- Obtain bacterial cultures if infection is suspected 4
Less Common Parasitic Causes (Travel History Dependent)
- Larva currens from Strongyloides stercoralis presents as itchy, linear urticarial rash moving 5-10 cm per hour on trunk, upper legs, and buttocks 7
- Onchocerciasis causes diffuse pruritic dermatitis over legs and buttocks, but has 8-20 month incubation period 7
- These are extremely unlikely without relevant travel history to endemic areas 7
Initial Management Approach
For Irritant Diaper Dermatitis
- Change wet and soiled diapers promptly 8
- Cleanse the diaper area and allow to dry completely 8
- Apply zinc oxide or petrolatum-based barrier ointment liberally with each diaper change, especially at bedtime 8, 9, 1
- Increase open air exposure to the diaper area 2
- Use baby wipes or water with washcloth for cleansing (both have comparable effects) 1
For Suspected Candidal Infection
- Apply topical antifungal (such as nystatin or ketoconazole) to affected areas 2
- Continue barrier protection with zinc oxide or petrolatum 1
For Seborrheic Dermatitis
- Use tar-containing shampoo, topical ketoconazole, or mild topical steroids for severe or persistent cases 3
- Apply mineral oil or petrolatum to soften scales before gentle removal 2
For Atopic Dermatitis
- Apply emollients liberally and frequently, at least twice daily 4
- Use mild potency topical corticosteroid (hydrocortisone) if significant inflammation present 6, 4
- Avoid irritants including harsh soaps and detergents 4