Langerhans Cell Histiocytosis Associated With Underlying Hematolymphoid Disorders in Adults: Report of 2 Cases and Review of the Literature.

Langerhans cell histiocytosis (LCH) is an uncommon disorder characterized by proliferation of abnormal LCs usually affecting children and adolescents. LCH in adults first presenting in the skin is rare. Although LCH and even LCH with a second malignancy may be more common in children, cutaneous LCH with a second hematologic malignancy has been more commonly identified in adults. The authors report 2 new cases of LCH in adult patients with underlying myelodysplasia and follicular lymphoma. The specimens were examined by routine microscopy and immunohistochemical stains for S100 protein and CD1a. Patients were elderly men with established diagnoses of follicular lymphoma and myelodysplasia, presented with follicular lesions and erythematous plaques involving intertriginous areas. Histologic examination revealed collections of mononuclear cells in upper dermis, which demonstrated strong positivity for S100 and CD1a, confirming their identity as LCs. BRAF analysis returned negative for detection of BRAF V600E mutation in both patients. The authors have recently encountered 2 cases of adult patients with skin-limited LCH predated by other lymphoproliferative disorders. The association between LCH and hematopoietic disorders may be explained by a common bone marrow precursor that is differentiating along different cell lines. Cutaneous LCH may be associated with underlying lymphoproliferative disorders and should be considered in the differential diagnosis of cutaneous eruptions in patients with hematopoietic disorders. Clinical follow-up evaluation of patients diagnosed with LCH for peripheral blood abnormalities and lymphadenopathy or "B symptoms" may be prudent in patients not already carrying a diagnosis of an underlying hematologic disorder.