Erdheim-Chester disease: a rare syndrome with a characteristic bone scintigraphy pattern.

Erdheim-Chester disease is a rare noninherited, non-Langerhans' cell histiocytosis, with multiorgan involvement. The skeleton is frequently involved in as many as 70-80% of all cases. In nearly half of the cases, there is an involvement of other organs such as the cardiovascular system, lung, kidneys, brain, and orbits. Extra-skeletal involvement is correlated with increased morbidity and mortality. In recent years, the disease is being described with increasing frequency although fewer than 200 cases have been identified worldwide. Besides its rarity, the disease has a characteristic almost pathognomonic bone scan appearance, which in some cases facilitates diagnosis of the syndrome. Bone scans also contribute to the qualitative assessment of skeletal involvement.