Langerhans Cell Histiocytosis - Classification

Classification

The disease spectrum results from clonal accumulation and proliferation of cells resembling the epidermal dendritic cells called Langerhans cells, hence sometimes called dendritic cell histiocytosis. These cells in combination with lymphocytes, eosinophils, and normal histiocytes form typical LCH lesions that can be found in almost any organ. A similar set of diseases has been described in Canine histiocytic diseases.

LCH is clinically divided into three groups: unifocal, multifocal unisystem, and multifocal multisystem.

Unifocal

Unifocal LCH, also called eosinophilic granuloma (an older term which is now known to be a misnomer), is a slowly-progressing disease characterized by an expanding proliferation of Langerhans cells in various bones. It is a monostotic or polystotic disease with no extraskeletal involvement. This differentiates eosinophilic granuloma from other forms of Langerhans Cell Histiocytosis (Letterer-Siwe or Hand-Schüller-Christian variant.

Multifocal unisystem

Seen mostly in children, multifocal unisystem LCH is characterized by fever, bone lesions and diffuse eruptions, usually on the scalp and in the ear canals. 50% of cases involve the pituitary stalk, leading to diabetes insipidus. The triad of diabetes insipidus, exopthalmos, and lytic bone lesions is known as the Hand-Schüller-Christian triad.

Multifocal multisystem

Multifocal multisystem LCH, also called Letterer-Siwe disease, is a rapidly-progressing disease in which Langerhans cells proliferate in many tissues. It is mostly seen in children under age 2, and the prognosis is poor: even with aggressive chemotherapy, the 5-year survival is only 50%.

Pulmonary Langerhans cell histiocytosis (PLCH) is a unique form of LCH in that it occurs almost exclusively in cigarette smokers. It is now considered a form of smoking-related interstitial lung disease. Some patients recover completely after they stop smoking, but others develop long-term complications such as pulmonary fibrosis and pulmonary hypertension.