Melorheostosis is a rare hyperostotic, benign, sclerosing bone dysplasia [1, 2]. It may present in a monostotic (involvement of one bone), polyostotic, or monomelic (involvement of one limb) form. The aetiology is controversial rather than definite. It was suggested that neural infection (analogous to herpes zoster) could result in lesions spread along the distribution of the associated sensory nerve root, with resultant scarring and hyperostosis [5]. Other suggestions of aetiology such as a vascular disorder, a degenerative lesion of connective tissue or embryonic damage have also been proposed [6]. Most interestingly, it has been thought to occur as a result of an embryonal metameric disturbance, which causes a failure in intramembraneous, and to a lesser extent, endochondral ossification [1]. One of the typical target sites of endochondral ossification is the skull base. In our patient, however, the persistence of subdental synchondrosis was either secondary to defective ossification of the first spinal sclerotome and or/it was secondary to the development of an asymptomatic non-union type II dens fracture [7].
Patients with melorheostosis usually present with pain and limitation of joint movement. The overlying skin may be tense, shiny, erythematous or hyperaemic. Muscle atrophy and linear scleroderma may be other features. Roger et al [3] reported a patient with features of melorheostosis associated with minimal change nephrotic syndrome, mesenteric fibromatosis and multiple capillary haemangiomas of the trunk. However, no hair and/or dental involvement was reported. Zeiller et al [8] reported the development of a severe myelopathy of the cervicothoracic spine associated with melorheostosis. Osteosarcoma and desmoid tumour were described in two separate reports in patients with melorheostosis [5].
Hellemans et al [9] have previously identified the gene locus of melorheostosis. It was found to be allelic with osteopoikilosis and Buschke-Ollendorff syndrome. They thought in might be allelic with melorheostosis [10]. Our patient, however, manifested melorheostosis as a symptom complex. The overall malformation complex was not relevant with previous reports [9, 10].
Differentiating melorheostosis from other sclerosing bone dysplasias is mandatory. Progressive diaphyseal dysplasia (Camurati-Engelmann syndrome) is characterised by a mixed sclerosing bone dysplasia affecting predominantly intramembraneous ossification that is inherited in an autosomal dominant fashion. Patients usually have symmetrical involvement of the extremities. Pathologically there is progressive bone formation along both the periosteal and endosteal surfaces of the long tubular bones. Radiologically there is sclerosis and thickening of the cortex of the skull and long bones, involving both the diaphyses and the metaphyses, but not the epiphyses [11]. Weismann-Netter-Stuhl syndrome is another sclerosing bone dysplasia (toxopachyosteose diaphysaire tibio-peroniere) also manifesting with progressive bone sclerosis, predominately involving the diaphyses and not the whole bone components [12]. Neither of these conditions fit the patient reported here.
Osteopoikilosis is another clinical entity of bone sclerosis in which the radiological lesions appear as small areas of bony sclerosis throughout the skeleton, although largely sparing the skull. The skin lesions may appear at any time from birth to adult life and consist of pea-sized papules of Buschke-Ollendorff syndrome [13]. Osteopathia striata is the combination of vertical striations of the metaphyses of the long bones, a large head with sclerosis, thickening of the skull vault and a variety of other manifestations including cleft palate, mental retardation, and sensorineural deafness or other signs of cranial nerve compression including facial paralysis [2]. All of these conditions were considered, but the overall clinical and radiographic features do not fit our patient.
Tricho-dento-osseous syndrome (TDO) was probably first described by Robinson and Miller [14]. The main features are enamel hypoplasia of the teeth, mild osteosclerosis (particularly of the skull), brittle nails and blond, dry, curly hair. All affected individuals have taurodontism, although with variable expression. 85% of affected individuals have kinky or curly hair. Ninety-seven percent of patients with TDO have thickened cranial bones without pneumatisation of the sinuses [13–15]. Melorheostosis has not been described in connection with TDO.
