Erdheim-Chester disease: a distinct lipoidosis or part of the spectrum of histiocytosis?

Erdheim-Chester disease has always been considered a distinct lipoidosis based on clinical and radiographic criteria. Pathologically, it has been indistinguishable from Hand-Schüller-Christian disease. Analysis of the 15 reported cases lends some doubt as to the diagnostic criteria. A new case is presented that strongly suggests that Erdheim-Chester disease is actually part of the spectrum of the histiocytoses.