Hemorrhagic Crusted Papule on the Arm

The Diagnosis: Self-healing Langerhans Cell Histiocytosis

Histopathologic examination showed an infiltrate of mononuclear cells with indented nuclei admixed with a variable dermal inflammatory infiltrate. Immunohistochemistry demonstrated cells that were strongly positive for CD1a (Figure, A) and langerin (Figure, B) antigens as well as S-100 protein (Figure, C), which was consistent with Langerhans cell histiocytosis (LCH).

Immunohistochemistry demonstrated cells strongly positive for CD1a (A), langerin (B), and S-100 protein (C)(all original magnifications×400). Reference bars indicate 20μm.

Histiocytoses are a heterogeneous group of disorders in which the infiltrating cells belong to the mononuclear phagocyte system.^1,2 Langerhans cell histiocytosis is the most common dendritic cell-related histiocytosis, occurring in approximately 5 per 1 million children annually, giving it an incidence comparable to pediatric Hodgkin lymphoma and acute myeloid leukemia.^1,2

Historically, there has been much debate about the pathogenesis of the disease.² Until recently it was unknown whether LCH was primarily a neoplastic or an inflammatory disorder. Although the condition initially was thought to have a reactive etiology,¹ more recent evidence suggests a clonal neoplastic process. Langerhans cell histiocytosis lesions are clonal and display malignancy-associated mechanisms such as immune evasion. Genome sequencing has revealed several mutations in precursor myeloid cells that result in the common downstream hyperactivation of the mitogen-activated protein kinase signaling pathway that regulates cell proliferation and differentiation.¹

Langerhans cell histiocytosis displays a wide spectrum of clinical phenotypes, which historically were subclassified as eosinophilic granulomas (localized lesions in bone), Hand-Schüller-Christian disease (multiple organ involvement with the classic triad of skull defects, diabetes insipidus, and exophthalmos), and Letterer-Siwe disease (visceral lesions involving multiple organs).³ However, in 1997 the Reclassification Working Group of the Histiocyte Society redefined LCH as single-system single site (SS-s) LCH, single-system multisite LCH, and multisystem LCH.⁴

In SS-s LCH, the most common site is bone (82%), followed by the skin (12%).⁵ Skin SS-s LCH classically presents as multiple skin lesions at birth without systemic manifestations; the lesions spontaneously involute within a few months.⁶ Less commonly, skin SS-s LCH can present as a single lesion. Berger et al⁷ described 4 neonates with unilesional skin SS-s LCH. Since then, more than 30 cases have been reported in the literature,⁸ and we report herein another unilesional self-healing LCH.

The morphology of skin lesions in self-healing LCH is highly variable, with the most common being multiple erythematous crusted papules (50%), followed by eczematous scaly lesions resembling seborrheic dermatitis in intertriginous areas (37.5%).^3,6 Unilesional self-healing LCH typically presents as an ulcerated or crusted nodule or papule on the trunk. This variability results in a large differential diagnosis. Self-healing LCH is easily mistaken for infectious processes including neonatal herpes simplex and varicella-zoster virus infection.⁹ Often, the dermatology department is consulted to rule out LCH when the asymptomatic neonate does not respond to parenteral acyclovir.

Less commonly, the magenta-colored papulonodules of self-healing LCH can mimic blueberry muffin rash and mandate a workup for intrauterine infections, especially cytomegalovirus, rubella, and blood dyscrasia.¹⁰ Other noninfectious processes in the differential of self-healing LCH include congenital infantile hemangioma, neonatal lupus erythematosus, seborrheic dermatitis (cradle cap), pyogenic granuloma, and psoriasis.^3,10 Definitive diagnosis requires histopathology.

Because unilesional self-healing LCH has an excellent prognosis and usually resolves on its own, therapy is unnecessary.^3,8 One large retrospective study (N=146) found that of all patients with skin lesions, 56% were managed with biopsy only.⁵ Other options include watchful waiting and topical corticosteroids. If the skin lesions are large, ulcerated, and/or painful, alkylating antitumor agents have been used. For extensive cutaneous disease, systemic corticosteroids combined with chemotherapy and psoralen plus UVA can be effective.⁶

The primary concern in the management of self-healing LCH is that the solitary skin lesion may be the harbinger of an aggressive disorder that can progress to systemic disease.⁵ Moreover, recurrent visceral or disseminated disease may occur months to years after resolution of solitary skin lesions.⁹ Studies have shown that localized and disseminated disease cannot be differentiated on the basis of clinical findings, histology, immunohistochemistry, or biomarkers.^3,11 As a result, an evaluation for systemic disease should be performed at the time of diagnosis for cutaneous LCH.^3,9 Minimum baseline studies recommended by the Writing Group of the Histiocyte Society include a complete blood cell count, liver function tests, coagulation studies, chest radiography, skeletal surveys, and urine osmolality testing.¹² Periodic clinical follow-up is recommended for all variants of LCH.⁹

Our case was diagnosed as self-healing LCH based on histologic findings. No treatment was required, and at 3-month follow-up the infant was asymptomatic without recurrence and was meeting all developmental milestones.