Eosinophilic Granuloma

Excerpt

Eosinophilic granuloma is the mildest variant of Langerhans cell histiocytosis (LCH), a group of disorders characterized by the abnormal proliferation of antigen-presenting Langerhans cells. First described by Lichtenstein and Jaffe in 1940, the term "eosinophilic granuloma" was later grouped with Hand-Schüller-Christian disease and Letterer-Siwe disease under the umbrella term "histiocytosis X," which referred to histiocyte proliferation of unknown cause. This classification was renamed Langerhans cell histiocytosis in subsequent years. Eosinophilic granuloma is a benign tumor-like condition where Langerhans cells, originating from myeloid dendritic cells rather than skin, proliferate abnormally. Eosinophilic granuloma is the most common form of LCH and accounts for <1% of all bone tumors.

The disease predominantly affects the axial skeleton, including the skull, jaw, spine, pelvis, ribs, and long bones, with long bone lesions typically located in the diaphysis. Adjacent soft tissues are often involved. The pattern of bone involvement varies with age: in children, the frontal bone of the skull is the most common site, while in adults, the jaw is more frequently affected. Similarly, the thoracic spine is commonly involved in children, whereas adults often exhibit cervical spine involvement. Other less frequently affected organs include the skin, pituitary gland, lungs, brain, liver, spleen, and gastrointestinal tract. Eosinophilic granuloma can present as a solitary lesion, which rarely requires treatment, or as a multisystem disease necessitating aggressive therapy.

Langerhans Cell Histiocytosis Classification

Langerhans cell histiocytosis is classified into 3 main types:

1. Eosinophilic granuloma

   1. Monostotic: A single bone lesion, observed in approximately 90% of cases.

   2. Polyostotic: Multiple bone lesions, found in about 10% of cases.

2. Hand-Schüller-Christian disease: A systemic condition presenting with the classic triad of exophthalmos, diabetes insipidus, and osteolytic skull lesions, Hand-Schüller-Christian disease typically affects children older than 3 years and has a worse prognosis due to extraskeletal involvement.

3. Letterer-Siwe disease: A severe systemic disease characterized by lymphadenopathy, skin rash, hepatosplenomegaly, and pancytopenia. Letterer-Siwe disease usually presents in children younger than 3 years and is frequently fatal.

The age-related differences in presentation, site predilection, and systemic involvement of eosinophilic granuloma underscore the importance of tailored evaluation and management strategies.