Erdheim-Chester disease: symmetric uptake in the (99m)Tc-MDP bone scan.

Erdheim-Chester disease (E-C D) is a rare clinicopathologic entity with nearly pathognomonic radiographic features. About half of the affected exhibit extraskeletal manifestations, including involvement of the hypothalamus-pituitary axis, lung, heart, retroperitoneum, skin, liver, kidneys, spleen and orbit. This disease usually affects individuals in their fifties to their seventies and has a male preponderance. The lesions of E-C D consist of lipid-storing CD68 (+) and CD1a (-) non-Langerhans cell histiocytes, either localized to the bone or involving multiple systems of the body as well. Skeletal involvement is characteristically bilateral and symmetric, exhibiting an osteosclerotic pattern in the metaphysis and diaphysis of the long bones, usually sparing epiphysis. We recently had a 68 years old male patient with E-C D, with a mild and persistent knee pain, who was subjected to a 3-phase technetium-99m methylene diphosphonate ((99m)Tc-MDP) bone-scan and subsequently to gallium-67 citrate ((67)Ga-C) whole body scan. The characteristic symmetric pattern of these scans raised the question of E-CD disease. The patient showed an excellent symptomatic response to high-dose steroids. However, the symptoms recurred after discontinuation of treatment.