DOI: 10.1148/radiol.2462050537
(Radiology 2008;246:638-640.)
© RSNA, 2008
The Dripping Candle Wax Sign1
Anu Bansal, MD
1 From the Department of Radiology, Brigham and Women's Hospital, Boston, Mass. Received March 30, 2005; revision requested May 25; revision received June 28; final version accepted August 22.
Address correspondence to the author, Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 S Kingshighway Blvd, St. Louis, MO 63110 (e-mail: bansala{at}mir.wustl.edu).
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APPEARANCE
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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 (Fig 1) (1–4).
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Figure 1: 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.
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EXPLANATION
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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 (2). Pathologic findings suggest both overproduction of bone matrix and increased angiogenesis (5). 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) (3).
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DISCUSSION
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Melorheostosis (also known as Leri disease) is a rare sclerosing bone dysplasia (6). 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 (1,4,7).
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 (8). It may affect a single bone (monostotic), a single limb (monomelic), or multiple bones (polyostotic) (1). There are reports (4,9) of several associated clinical entities, including sclerodermic skin changes. These often involve the skin that overlies the affected areas of bone (10). Associations with vascular tumors and malformations have also been reported (9), suggesting an inherent defect in angiogenesis. Hemangiomas, glomus tumors, and arteriovenous malformations have all been described in patients with melorheostosis.
Although melorheostosis has classically been described as having the appearance of flowing hyperostosis, a case series of 23 patients (4) has demonstrated varied radiologic presentations. The authors describe five patterns: osteoma-like, myositis ossificans–like, osteopathia striata–like, classic, and mixed. In their study population, only five patients were found to have classic radiographic findings. The diagnosis can also become complicated by overlap syndromes (the radiographic appearance of more than one sclerosing bone dysplasia). The most common overlap syndrome is one in which features of osteopoikilosis, osteopathia striata, and melorheostosis are all present, leading some investigators to the conclusion that these entities may have a common pathogenesis (2).
Recently, genetic work (11) in several families with osteopoikilosis, melorheostosis, and Buschke-Ollendorff syndrome (BOS; osteopoikilosis associated with disseminated connective tissue nevi) has supported the theory that some sclerosing bone dysplasias may have a common origin. Hellemens et al (11) demonstrated that a loss-of-function mutation in LEMD3 (on chromosome 12q) results in osteopoikilosis, BOS, and melorheostosis. In addition, they were able to disprove the hypothesis advanced by some investigators (12) that BOS and melorheostosis are caused by a "second-hit" somatic mutation. Further work by another group (13) demonstrated that this gene codes for an inner nuclear membrane protein that normally inhibits both transforming growth factor β and bone morphogenic protein, the upregulation of which could be responsible for the clinically observed phenotypes in these conditions.
In summary, 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 (14) (Fig 2). 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 (15,16).
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Figure 2: Noncontiguous transverse CT images through eighth (left) and ninth (right) right posterior ribs of patient in Figure 1 show sharp delineation between normal and affected bone segments (arrows), highlighting sclerotomal distribution.
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FOOTNOTES
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Author stated no financial relationship to disclose.
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References
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- Greenspan A, Azouz EM. Bone dysplasia series: melorheostosis—review and update. Can Assoc Radiol J 1999;50:324–330. [Medline]
- Greenspan A. Sclerosing bone dysplasias: a target site approach. Skeletal Radiol 1991;20:561–583. [CrossRef][Medline]
- Murray RO, McCredie J. Melorheostosis and the sclerotomes: a radiological correlation. Skeletal Radiol 1979;4:57–71. [Medline]
- Freyschmidt J. Melorheostosis: a review of 23 cases. Eur Radiol 2001;11:474–479. [CrossRef][Medline]
- Hoshi K, Amizuka N, Kurokawa T, Nakamura K, Shiro R, Ozawa H. Histopathological characterization of melorheostosis. Orthopedics 2001;24:273–277. [Medline]
- Leri A, Joanny JP. Une affection non décrite des os: hyperostose "en coulée" sur toute la longueur d'un membre ou "mélorhéostose." Bull Mem Soc Med Hop Paris 1922;46:1141–1145.
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- Kessler HB, Recht MP, Dalinka MK. Vascular anomalies in association with osteodystrophies: a spectrum. Skeletal Radiol 1983;10:95–101. [CrossRef][Medline]
- Aytekin S, Gezici AX, Anadolu KX. Melorheostotic skin changes. Int J Dermatol 2002;41:612–614. [CrossRef][Medline]
- Hellemans J, Preobrazhenska O, Willaert A, et al. Loss-of-function mutations in LEMD3 result in osteopoikilosis, Buschke-Ollendorff syndrome and melorheostosis. Nat Genet 2004;36:1213–1218. [CrossRef][Medline]
- Nevin NC, Thomas PS, Davis RI, Cowie GH. Melorheostosis in a family with autosomal dominant osteopoikilosis. Am J Med Genet 1999;82:409–414. [CrossRef][Medline]
- Lin F, Morrison JM, Wu W, Worman HJ. MAN1, an integral protein of the inner nuclear membrane, binds Smad2 and Smad3 and antagonizes transforming growth factor-beta signaling. Hum Mol Genet 2005;14:437–445. [Abstract/Free Full Text]
- Nasu K, Kuroki Y, Nawano S, et al. Thoracic cage extent of melorheostosis depicted by multislice CT. Skeletal Radiol 2002;31:464–466. [CrossRef][Medline]
- Judkiewicz AM, Murphey MD, Resnik CS, Newberg AH, Temple HT, Smith WS. Advanced imaging of melorheostosis with emphasis on MRI. Skeletal Radiol 2001;30:447–453. [CrossRef][Medline]
- Mahoney J, Achong DM. Demonstration of increased bone metabolism in melorheostosis by multiphase bone scanning. Clin Nucl Med 1991;16:847–848. [CrossRef][Medline]
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