How is Hereditary multiple exostoses diagnosed?

Hereditary multiple exostoses (HME) is primarily diagnosed through clinical physical examination combined with radiographic imaging, such as X-rays, to identify characteristic bony outgrowths near the growth plates. While genetic testing can confirm mutations in the EXT1 or EXT2 genes, the diagnosis is often established based on the presence of two or more osteochondromas in long bones, as identified by a specialist.

How is Hereditary multiple exostoses diagnosed?

The diagnostic process for Hereditary multiple exostoses typically begins when a child or adolescent presents with painless, palpable bony bumps near the joints. A physician will perform a physical exam to assess the size and location of these masses. Because Hereditary multiple exostoses is a skeletal disorder, the primary diagnostic tool is imaging. Radiographs (X-rays) of the entire skeleton—often referred to as a "skeletal survey"—are usually required to document the number and distribution of the exostoses. In some cases, MRI or CT scans are utilized if there is a concern about nerve compression or to evaluate the thickness of the cartilage cap, which is important for monitoring potential malignant transformation.

Is genetic testing required for a diagnosis?

While clinical findings are often sufficient for a diagnosis, molecular genetic testing is available and can provide definitive confirmation. Approximately 90% of individuals with Hereditary multiple exostoses have an identifiable mutation in either the EXT1 or EXT2 genes. Genetic testing is particularly valuable for family planning and identifying asymptomatic carriers within a family. However, a negative genetic test does not definitively rule out Hereditary multiple exostoses, as some patients may have mutations in regions of the gene not covered by standard sequencing panels.

What is the diagnostic process and the "diagnostic odyssey"?

For many, the path to a diagnosis of Hereditary multiple exostoses is frustratingly long. Patients often experience a "diagnostic odyssey" where they see multiple general practitioners or pediatricians before reaching a specialist who recognizes the pattern of skeletal growth. The following steps are standard in the clinical workup:

• Clinical History: Reviewing the family history, as the condition follows an autosomal dominant inheritance pattern.


• Physical Exam: Palpating the limbs for firm, immobile masses near the knees, ankles, or shoulders.


• Skeletal Survey: A series of X-rays to map the total number of exostoses.


• Genetic Counseling: Consultation to discuss the 50% inheritance risk for offspring and to confirm the mutation.


• Differential Diagnosis: Distinguishing Hereditary multiple exostoses from solitary osteochondromas, metachondromatosis, or enchondromatosis.

Which specialists should lead the care team?

It is common for families to feel unheard when visiting doctors unfamiliar with rare bone conditions. We strongly encourage you to seek care from a pediatric orthopedist or a geneticist with specific experience in skeletal dysplasias. These specialists are best equipped to distinguish Hereditary multiple exostoses from other bony conditions and can provide a personalized monitoring plan, which is crucial given the rare but significant risk of chondrosarcoma (malignant transformation) in adulthood. Currently, 266 people with Hereditary multiple exostoses have shared their experiences on DiseaseMaps.org, highlighting the value of connecting with a community that understands the nuances of this diagnosis.

Next steps

• Request a referral to a pediatric orthopedist or a center specializing in skeletal dysplasias.


• Collect your family medical history to assist your genetic counselor in identifying inheritance patterns.


• Join the Hereditary multiple exostoses community on DiseaseMaps.org to share experiences and find peer support.


• Maintain a log of any new or rapidly growing bumps to discuss with your specialist during follow-up appointments.

Medical disclaimer: This information is for educational purposes only and does not constitute medical advice, diagnosis, or treatment; always consult with a qualified healthcare provider regarding your specific medical condition.

References

• NIH Genetic and Rare Diseases (GARD) Information Center: Hereditary multiple exostoses.


• Orphanet: Multiple osteochondromas (ORPHA:323).


• OMIM (Online Mendelian Inheritance in Man): Entry #133700 (EXT1) and #133701 (EXT2).


• The MHE Research Foundation: Patient resources and educational materials.