various disorders that share the characteristic of abnormal histiocytes (macrophages) (Table 1).
Histiocytosis, Table 1. Some forms of histiocytosis.
The Langerhans cell histiocytoses (or histiocytosis X) may be classified according to the following scheme:
Letterer Siwe disease, the acute form, with rapid dissemination and poor clinical prognosis.
In all three forms specific histiocytic cells (Langerhans cells) containing cytoplasmic inclusion bodies (Langerhans granules or X bodies) can be identified. However, some authorities believe that the early and diffuse organ involvement and rapid patient death that occur in Letterer Siwe disease support its classification as a malignant lymphoma, and eosinophilic granuloma resembles more an inflammatory process than a neoplasm.
In general, bone scintigraphy has proved to be less sensitive than radiography in the detection of bone lesions in the histiocytoses. The purely lytic nature of the lesions may explain the disappointing results. Those abnormalities that are present on bone scans show a spectrum of radionuclide abnormalities ranging from areas with decreased or absent accumulation of the radionuclide to areas of augmented activity.
Spin-echo MR imaging of the skeleton in patients with histiocytosis may reveal one or more foci of decreased signal intensity on T1-weighted images and of increased signal intensity on T2-weighted images. A malignant tumour or infection and stress fractures may have the same MR imaging features as the histiocytoses.
Sinus histiocytosis with massive lymphadenopathy, also known as Rosai Dorfman disease, is a non-neoplastic, self-limiting disease of unknown cause. It is typically manifested as painless adenopathy, fever, elevated erythrocyte sedimentation rate, neutrophilic leukocytosis and hypergammaglobulinaemia. Involved lymph nodes reveal a marked proliferation of sinus histiocytes. Extranodal sites of involvement include the upper respiratory tract, salivary glands, orbits, eyelids, testes and bone. The bone manifestations of this disease are generally restricted to multiple or, less frequently, solitary asymptomatic osteolytic lesions involving principally the long tubular bones. However, the skull, pelvis, sternum, vertebral bodies, phalanges, metacarpals and ribs may also be involved.
The major features of malignant histiocytosis include fever, weight loss, hepatosplenomegaly, jaundice and progressive pancytopenia with histiocytic infiltration in lymph nodes, liver, spleen and bone marrow. Radiographically evident bone lesions are not uncommon, appearing as osteolytic foci with sclerotic margins. The pelvis, spine and tubular bone are involved. These lesions may disappear during treatment.