Anatomic Pathology: Skin Pathology

• Langerhans cell histiocytosis previously was divided into multiple clinical subtypes, but there is much overlap. The different forms of Langerhans cell histiocytosis have similar pathology in that there is a proliferation of Langerhans cells, which can be identified by the distinctive reniform, or kidney-shaped, nuclei.

• Langerhans cells stain positively with S-100 protein and CD1a immunohistochemical stains. Langerhans cells do not stain with CD68.

• With electron microscopy, characteristic Birbeck granules are seen within Langerhans cells. The Birbeck granules resemble a tennis racquet.

• Letterer-Siwe disease is the acute disseminated form of Langerhans cell histiocytosis. It is usually seen in infants and has many systemic manifestations. The skin lesions are characterized by hyperpigmented scaly patches, which can coalesce and form a seborrheic dermatitis–like eruption. An unresponsive dermatitis in the diaper area is one recognizable presentation. In the case presented here, the hyperpigmented papules with associated hemorrhage at the periphery of the dermatitis area are a clue to the diagnosis.

• Hand-Schüller-Christian disease is a form of Langerhans cell histiocytosis that is characterized by the triad of bone lesions, exophthalmos, and diabetes insipidus. Eosinophilic granuloma is a form of Langerhans cell histiocytosis that usually consists of either a few lesions or one lesion and most commonly affects the bone. The skin and oral mucosa occasionally can be involved.

• Congenital self-healing reticulohistiocytosis, also known as Hashimoto-Pritzker disease, is a variant of Langerhans cell histiocytosis with a very good prognosis. Lesions are often present at birth but can manifest within the first few weeks of life as well. Most commonly, there are scattered papules and nodules over the skin; occasionally, only a single lesion is present.