Clinical History
The patient, an 80-year-old woman, presented to the emergency department for respiratory distress. A chest X-ray and a CT were performed. The patient had clinical history of osteoarthritis.
Imaging Findings
The chest X-ray (Fig. 1) showed an undulating irregular hyperostotic cortical pattern along the long axis of multiple left ribs and the first right rib, resembling melting wax dripping down the side of a candle - the "dripping candle wax sign". Also note the heterogeneous amorphous calcifications around the shoulder joint and scapula.
Axial CT images of the chest revealed undulating irregular sclerotic changes affecting mostly the left ribs (Fig. 2a-f) but also the first right rib (Fig. 2a), a spinous process (Fig. 2c), the left scapula (Fig. 2a-c) and a costovertebral joint (Fig. 2g).
Discussion
Melorheostosis (also known as Leri disease) is a rare sclerosing bone dysplasia [1]. Men and women are equally affected and the prevalence of the disease is 0.9 per million. The age of presentation ranges from 2 to 64 years, with approximately half the cases being diagnosed before 20 years of age [2].
Clinical manifestations of melorheostosis are variable, ranging from chronic pain, joint stiffness, deformity, contractures and muscle wasting. Patients may be asymptomatic and the disease can present as an incidental finding on imaging [3].
There are several radiological patterns described, including osteoma-like, candle-wax appearance (the classic pattern), osteopathia striata-like, soft tissue calcifications and a mixed pattern.
The dripping candle wax appearance consists of irregular thickening of cortical bone, with thick undulating ridges of bone, reminiscent of molten wax [4]. This sign was described initially on conventional radiographs, although the findings are similar on computed tomography (CT) [3 - 5].
The differential diagnosis includes osteophatia striata, osteopoikilosis, osteosarcoma and myositis ossificans. There are some imaging findings that may allow differentiation from melorheostosis, although the correct diagnosis is not always easy due to imaging features overlap and the existence of overlap syndromes, in which features of two or more sclerosing dysplasias are combined, a combination of melorheostosis, osteopoikilosis and osteopathia striata being the most frequent. The presence of longitudinal dense striations in osteopathia striata, punctate, rounded bone islands surrounding joints in osteopoikilosis, bone destruction in osteosarcoma, and soft tissue ossification in myositis ossificans may help differentiate from melorheostosis, although some of them are present in melorheostosis as well [6].
Most cases are benign and do not require operative intervention, with only conservative measures such as manipulation, analgesia, physical therapy, bisphosphonates and casting being used. More invasive therapies for severely symptomatic cases consist of surgical soft-tissue procedures and even, in very severe cases, amputation [7].
Differential Diagnosis List
Polyostotic melorheostosis
Osteopathia striata
Osteopoikilosis
Osteosarcoma
Myositis ossificans
Final Diagnosis
Polyostotic melorheostosis
