DEFINITION
Melorheostosis is a rare and progressive disorder characterized by hyperostosis (thickening) of the cortical bone.
The lesions are usually asymmetric and involve only one limb or correspond to a particular sclerotome.
They may be accompanied by abnormalities of adjacent soft tissue, including joint contractures, sclerodermatous skin lesions, muscle atrophy, or hemangiomas.
The des ignation combines root words meaning “limb”, “flow”, and “bone”.
The disease is associated with the mutation of LEMD3 Gene .
EPIDEMIOLOGY
Melorehostosis has an estimated incidence 1:1,000,000.
Although changes occur in early childhood age at presentation is often later, and the condition often remains occult until late adolescence or early adulthood.
In only approximately half of cases is the diagnosis made before the age of 20.
There is no recognised familiaR predisposition.
(The Dripping Candle Wax Sign, 2008)
SYMPTOMS
Onset is usually insidious and the main symptoms are:
- deformity of the extremity;
- limitation of motion in the joints.
The first manifestation is in late childhood or early adolescence and it progresses into adult life.
The characteristic radiographic appearance consists of irregular hyperostotic changes of the cortex , generally on one side of the bone, resembling melted wax dripping down one side of a candle. This appearance gave the anomaly its name, which is taken from the Greek words for member ( melos ) and flow ( rhein ).
There is usually a distinct demarcation between the affected and normal bone. Dense, sclerotic linear areas are seen mainly in the cortex but also extending into the cancellous bone. Melorheostosis affects mainly the long bones of the upper and lower limbs, but also the short bones of the hand and foot and, rarely, the axial skeleton.
It may co-exist with Osteopoikilosis and Osteopathia Striata as well as with tumours or malformations of blood vessels or lymphatics.
Soft-tissue ossifications at the site of the joint are common .
(Bone Dysplasia Series. Melorheostosis: Review and Update, 1999)
DIAGNOSIS
The main diagnostic tools are:
- X-ray
Cortical hyperostosis is readily seen on plain radiographs, extending along the lenghth of one side of the bone and resembling flowing candle wax.
In the carpal and tarsal bones and in the epiphyses, the hyperostosis may be round or irregular,
Involvement of the axil skeleton is rare. Soft tissue calcification or ossification may be seen.
- Scintigraphy
Scintigraphy reveals abnormal increased tracer uptake in the bone and soft tissue lesions.
It may be instrumental in confriming the diagnosis in equivocal cases.
- Computed Axial Tomography
Computed tomography will also reveal the lesion and the clear demarcation between normal and abnormal bone.
- RMN
Magnetic resonance imaging show the bone and soft tissue lesions as areas of low signal, on al sequences.
Computed tomography and Magnetic resonance imaging are not need for diagnosis in the vast mojority of cases, especially in children.
Differential diagnosis
Iparosteal osteosarcoma may be in the differential diagnosis in more localized forms, and myositis ossifications or calcified hematoma in cases associated with soft tissue calcification or ossification.
(Melorheostosis,2005 )
PATHOGENESIS
LEMB3
Histological analysis reveals dense bone without distinctive cellular abnormalities; however, the microscopic appearance of lesions is not identical in all cases.
Histologic findings include variable degrees of cortical thickening consisting of chondroid islands surrounded by woven or non-lamellar dense bone depending on stage of maturation with thickened, sclerotic, and irregular lamellae.
An adjacent zone of fibrocartilage with irregular surface fibrillation is also observed.
A large quantity of osteoid without mineralization suggests overproduction of bone matrix in affected bone.
However, osteoclasts are more numerous, reflecting increased bone resorption.
This indicates that increased bone formation and bone resorption are combined processes in melorheostosis.
Soft tissue abnormalities consisting of osseous, chondroid, vascular, and fibrocartilaginous tissue have been reported in 76% of cases of melorheostosis.
Rarely, presence of a cartilage cap over a portion of the sclerotic bone has been described in intra-articular melorheostosis, and that could lead to misinterpreting the lesion as an osteochondroma, a bizarre parosteal osteochondromatous proliferation, or an even more concerning parosteal osteosarcoma.
(Melorheostosis: ClinicoPathological Features, Diagnosis and Management, 2009 )
TREATMENT
Surgery to alleviate mechanical effects from melorheostosis in adults seems to be fairly
effective. This is particularly true when the mechanical effects are mostly due to asymmetric
bone growth, producing a deformity that can be corrected with bone procedures alone. As soft
tissue causes of deformity increase, the need for osseous, soft tissue, and skin correction
increases. In this case, surgery is less likely to produce satisfactory results, unless amputation
is deemed an appropriate procedure.
Surgery for the sole purpose of relieving pain (non-mechanical) in melorheostosis is rarely
effective, unless that pain is a direct result of nerve pressure or irritation.
Enrico G. Spinoni
Stefano Tappero
