What is melorheostosis?

What is Melorheostosis

Melorheostosis is a rare, non-hereditary sclerosing bone dysplasia characterized by irregular cortical hyperostosis that resembles dripping candle wax flowing down one side of a bone, typically affecting the long bones of the lower extremities in a sclerotomal distribution. 1, 2

Clinical Characteristics

Demographics and Presentation:

• Affects men and women equally with no hereditary pattern identified 1, 3
• Can present at any age, though symptoms typically manifest in late childhood or early adolescence and progress into adult life 3
• Onset is insidious, with pain being the most common presenting symptom 1, 2

Clinical Features:

• Lower limb deformity is the most common presentation 2
• Progressive joint stiffness and limitation of motion 3
• Extremity swelling and deformity 1, 4
• Hyperpigmented skin overlying affected areas may be present 1
• Soft-tissue ossifications at joint sites are common 3
• Neurological symptoms including anesthesia can occur in severe cases 4

Radiological Diagnosis

Classic Imaging Findings:

• The pathognomonic feature is extensive, dense, undulating or irregular cortical hyperostosis resembling hardened wax dripping down the side of a candle 1, 3
• Hyperostotic changes are typically irregular and generally confined to one side of the bone 3
• Dense, sclerotic linear areas appear mainly in the cortex but can extend into cancellous bone 3
• Distinct demarcation between affected and normal bone 3

Distribution:

• Primarily affects the appendicular skeleton, particularly long bones of upper and lower limbs 2, 3
• Can involve short bones of hands and feet 3
• Rarely affects the axial skeleton 1, 3
• Usually follows a sclerotomal distribution 2

Advanced Imaging:

• Bone scintigraphy shows moderately increased tracer uptake 3
• CT scans demonstrate classic candle wax-like hyperostosis and narrowing or disappearance of the medullary cavity 4
• MRI can characterize the lesion and evaluate soft tissue involvement 3

Pathogenesis

Current Understanding:

• The exact etiology remains unknown 1, 2
• LEMD3 gene mutations have been demonstrated in several familial cases but are more strongly correlated with other hereditary dysplasias like osteopoikilosis 2
• Proposed mechanisms include somatic LEMD3 mutations, somatic mutations in the bone morphogenetic protein/transforming growth factor-beta pathway, mutations in multiple genes, or non-genetic causes 2
• Classic sporadic melorheostosis likely has a different causative mechanism than familial cases 2

Associated Conditions

Overlap Syndromes:

• May co-exist with osteopoikilosis and osteopathia striata 3
• Can present with mixed or atypical osseous involvement in addition to classic "dripping candle wax" appearance 2
• Some patients have overlap with Buschke-Ollendorff syndrome 2
• May be associated with tumors or malformations of blood vessels or lymphatics 3

Laboratory Findings

Routine laboratory findings are usually normal 1

Management Approach

Current Treatment Options:

• No definitive cure exists; treatment is primarily symptomatic 1, 5
• Nitrogen-containing bisphosphonates (particularly pamidronate) have shown benefit in recent years 1, 2
• Physical therapy for deformity management and joint mobility 1, 2
• Analgesics for pain control 1
• Traditional orthopedic surgical approaches for severe deformity 2, 3
• Surgical soft-tissue procedures may be necessary 3
• In very severe cases, amputation may be required 3

Prognosis:

• This is a chronic and sometimes debilitating condition 3
• Progressive nature with symptoms worsening over time 3
• Better characterization of genetic and developmental factors may lead to targeted therapy in the future 2

Differential Diagnosis Considerations

The forme fruste (incomplete form) of melorheostosis may mimic:

• Myositis ossificans 3
• Osteoma 3
• Parosteal osteosarcoma 3

Histologic analysis confirms the diagnosis and reveals extremely dense sclerotic bone of cortical pattern 4