The Dripping Candle Wax Sign

Dripping Candle Wax.

The dripping (or flowing) candle wax sign is seen on conventional radiographs depicting bone. The appearance is that of irregular cortical hyperostosis, typically occurring on one side of the involved bone, and has been likened to melted wax flowing down one side of a candle.

The dripping candle wax sign indicates melorheostosis. The radiographic findings may reflect a developmental error primarily in intramembranous bone formation. This leads to an irregular thickening of cortical bone (cortical hyperostosis) that extends up to (but usually not past) the articular surface. Pathologic findings suggest both overproduction of bone matrix and increased angiogenesis. The distribution of affected bone is thought to be due to the predilection of melorheostosis to occur in sclerotomes (skeletal regions innervated by a single spinal sensory nerve).

Preoperative posteroanterior chest radiograph of a man presenting for excision of facial arteriovenous malformation.

Note irregular flowing hyperostosis (arrows) along caudal surface of the eighth and ninth right posterior ribs.                       

Melorheostosis (also known as Leri disease) is a rare sclerosing bone dysplasia. The name is derived from the Greek words for limb (melos) and flow (rhein), due to its characteristic appearance of flowing hyperostosis. Patients are often asymptomatic, with the condition diagnosed as an incidental finding on radiographs obtained for another purpose.

When melorheostosis does manifest clinically, the most common presentation is of limb stiffness or pain. Although the age at presentation varies, it usually remains occult until late adolescence or early adulthood. The disease follows a chronic progressive course, occasionally resulting in substantial disability that may lead to amputation.

Melorheostosis predominantly affects the appendicular skeleton and is most common in the long bones of the upper and lower extremities, although it can be seen in the hands and feet as well. Melorheostosis has rarely been reported in the axial skeleton. It may affect a single bone (monostotic), a single limb (monomelic), or multiple bones (polyostotic).

The dripping candle wax sign on conventional radiographs indicates melorheostosis. Although other imaging techniques are rarely necessary for diagnosis, similar findings can be noted on computed tomographic (CT) scans. Magnetic resonance imaging depicts decreased signal intensity of affected bone on images obtained with all pulse sequences, while radionuclide bone scanning reveals moderate and asymmetric increased uptake.

Non-contiguous transverse CT images through eighth (left image) and ninth (right image) right posterior ribs of same patinet with previous plain chest X-ary show sharp delineation between normal and affected bone segments (arrows), highlighting sclerotomal distribution.