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The word melorheostosis is just as difficult to spell and pronounce as it is unusual. This non-hereditary bone disease, which can affect both males and females, is extremely rare, and it affects not only the bone but the soft tissue, as well. It is a progressive skeletal disease characterized by the thickening of the outer layer of the bones. Despite its benign status, it can contribute to significant pain and deformity and may also result in functional limitation.
The bone disease typically emerges in childhood, sometimes in the first few days after birth. Of those affected, 50% will develop symptoms by their 20th birthday. While just a few hundred cases have actually been reported, it is estimated that there are approximately one million to 1.5 million people with melorheostosis.
When an adult is affected by melorheostosis, the chief complaints include pain, stiffness in the joints and progressive deformity. When seen in pediatric cases, this rare bone disease usually affects the bones in the extremities and in the pelvis. Such symptoms could cause differences in limb lengths, deformity or the inability to recognize a full range of motion in the joints, and there may also be formations that occur outside of the bone, known as extraosseous bone formation.
While the exact cause of melorheostosis is not known, one theory suggests that the condition is born from an abnormality of the sensory nerve of the affected sclerotome. A sclerotome, by medical definition, is a zone of the skeleton supplied by an individual spinal sensory nerve, representing a basic unit of embryonic development. This may involve just one bone or several bones.
What doctors do know about this extremely painful bone disease is that it causes new bone to abnormally grow on top of normal bones. When viewed on x-rays, melorheostosis resembles dripping wax down a candle. This new growth is usually quite hard, and has been so hard in some cases that it actually breaks surgical instruments.
It can run its course from being fairly benign to extremely painful. Some patients may not even know they have melorheostosis until revealed by an x-ray.