Gorham disease: Also called disappearing bone disease. Extensive loss of calcium from a single bone so that it cannot be seen on x-ray. Any bone can be involved but the upper arm, shoulder, and jaw are most frequent. This type of selective decalcification is sometimes associated with the presence of an hemangioma, a knot of distended blood vessels. The synonyms for this condition include invisible bone disease, vanishing bone disease, phantom bone disease and massive osteolysis.