Young children commonly demonstrate rashes. The underlying diagnoses are often straight forward, but unusual cases or rashes that do not respond to conventional treatment should be promptly investigated. A report describes a case of a 4-month-old with a persistent scalp rash and a milk protein allergy who was admitted to the hospital for failure to thrive and suspected pneumonia.

Ten discrete, skin-colored papules on the scalp, were observed several of which were erythematous, hemorrhagic or had yellow crust. Macerated skin and several ulcerative lesions were also observed in the neck folds and submental skin. Seven skin-colored, umbilicated papules were observed in the anterior chest. No lesions were seen in the diaper area or on the extremities.

A diagnosis of Langerhans cell histiocytosis was confirmed with a biopsy, which is a rare, inflammatory, neoplastic disorder of myeloid dendritic cells that causes infiltration of organs of the body. 

Cutaneous disease is the commonest manifestation of Langerhans cell histiocytosis in patients younger than 2years; however, it is rarely limited to the skin. Systemic involvement is observed in 87% to 93% of patients with cutaneous findings, and children younger than 3years generally have an acute disseminated multisystem disease. 

In children, particularly infants, Langerhans cell histiocytosis typically presents with scaly, red-brown, seborrheic dermatitis-like papules or an eczematous, erythematous, scaly eruption on the scalp and flexural folds. Erosions in the flexural folds are frequent. Langerhans cell histiocytosis shows many probable cutaneous morphologies, and petechiae, purpura or hemorrhagic crusts should raise suspicion.

Despite the rarity, it should be considered in children with atypical rashes or those recalcitrant to treatment. High clinical suspicion for systemic disease is critical in children younger than 3years to prevent diagnostic delay and manage appropriately.

Source: Shafique DA, McCann S, Kimes K. Case report: four-month-old with failure to thrive and a rash. Am Fam Physician. 2022;105(2):114-5.