It was Erdheim-Chester disease.
This rare disease is characterized by a symmetrical sclerosis at the diametaphyseal portions of the lower extremities with additional extraskeletal involvement. It is rare with less than 100 cases reported in the literature. Radiographic studies reveal a bilateral, patchy or diffuse increase in density, coarsened trabecular pattern, sclerosis, and cortical thickening mainly in the metaphyses with minor changes or sparing of the epiphyses. Many internal organs and tissue sites, including the kidney and retroperitoneum, lung, pericardium, skin, orbit, and brain may occur. The symptoms and clinical manifestations depend upon the organ involved. Infiltration of the pituitary stalk may lead to diabetes insipidus while involvement of the lungs may lead to diffuse pulmonary fibrosis.
Under the microscope, there is diffuse infiltration of the affected organs by lipid-laden histiocytes and Touton-type giant cells. These cells resemble Langerhans cells but immunohistochemistry reveals important differences (see table below).
For many years, this disease has been considered a variant of Langerhans cell histiocytosis (LCH). In particular, there was similarity to a variant of LCH known as Hand-Schuller-Christian disease. However, there are important differences. Based upon these recent studies, it is likely that this disease is distinct from LCH. The prognosis is poor with progressive disease with resultant organ-system dysfunction. Mortality is 57% usually from respiratory distress, cardiac failure, or pulmonary fibrosis.
