Background: Melorheostosis, also known as Leri disease or flowing periosteal hyperostosis is an uncommon, non-hereditary, benign, mesodermal mixed sclerosing bone dysplasia that affects both cortical bone and adjacent soft tissue structures in a sclerotomal distribution [1]. Sclerosing bone dysplasias are characterised by unique skeletal abnormalities, with each disorder representing unique disruptions of the bone developmental pathway. Melorheostosis usually affects one bone or multiple bones of a single extremity. It also favours the lower extremities, spares the skull and face, and rarely involves the spine.
Clinical Perspective: Melorheostosis typically presents in teenage years or early adulthood. It is slowly progressive and usually stabilises in adulthood. The most common presentation of this disease is an incidental finding. When symptomatic, it presents with pain or joint stiffness. Soft tissue involvement has the same dermatomal distribution as osseous changes and may present as subcutaneous fibrosis, erythema, ectopic bone formation, oedema or vascular tumours and malformations. Limb length discrepancy may develop due to asymmetric early fusion of epiphyses [2].
Imaging Perspective: Diagnosis of melorheostosis is based on a combination of clinical and radiological features that help to differentiate this condition from other sclerosing bone dysplasias.
The best imaging tool for diagnosis is plain radiography, which is usually sufficient to establish a certain diagnosis. Five patterns have been described. The classical pattern of presentation consists of periosteal cortical thickening that may be endosteal with intramedullary extension. Melorheostosis causes a thick undulating appearance along the cortex similar to “melting wax dripping down a candle” [2, 3]. The disease is confined to sclerotomes and rarely extends beyond margins of the bone into a joint. The other possible patterns are “osteoma-like”, “osteopathia striata-like” and “myositis ossificans-like”. The most common presentation is a mixed pattern consisting of one or more features of these four radiological presentations [4].
Computed tomography shows osseous sclerosis and reduction of the medullary space at higher resolution than does plain radiography.
Magnetic resonance imaging usually shows low signal on all imaging sequences, with no enhancement.
In nuclear medicine, an increase in radiotracer uptake is usually present on late phase bone scans [5].
Outcome: The disease is of variable severity, but in general follows a chronic progressive course in adults and a faster course in children, occasionally resulting in substantial disability from contractures or deformity. The treatment aimed at reducing pain and stiffness if present. Bisphosphonates are reported to relieve symptoms [6].
Teaching Points: The diagnostic key of melorheostosis is plain radiography with the classical appearance of dripping candle wax.
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