Multiple Cartilaginous Exostoses in Dogs: Symptoms, Causes, and Diagnosis

Multiple cartilaginous exostoses (MCE) in dogs are a benign bone disorder characterized by the development of cartilage-capped bony projections on the surfaces of bones. These lesions most commonly develop during skeletal growth and may affect the limb bones, ribs, and vertebrae. Their size and anatomical location determine their potential impact on surrounding tissues and the severity of clinical signs.

Osteochondromas and multiple cartilaginous exostoses in dogs are bone lesions associated with skeletal development. Although they commonly occur in young dogs, some lesions remain asymptomatic, while others may cause pain, restricted movement, or neurological abnormalities due to pressure on adjacent structures.

What Are Cartilaginous Exostoses?

An exostosis is a bony projection that grows outward from the surface of a bone. Osteocartilaginous exostoses are lesions composed of bone and cartilage, covered by a layer of cartilage.

A single lesion is generally referred to as an osteochondroma. When multiple osteochondroma-like lesions occur in the same animal, the condition is described as multiple cartilaginous exostoses (MCE).

These lesions may develop in bones that form through endochondral ossification. The metaphyseal region of long bones is one of the important anatomical locations where osteochondromas may occur.

Although cartilaginous exostoses are generally benign, their location, growth pattern, and relationship with surrounding tissues must be considered during clinical evaluation.

Causes of Cartilaginous Exostoses in Dogs

The exact cause of multiple cartilaginous exostoses in dogs remains unclear. However, genetic factors are suspected to contribute to the development of this condition.

Autosomal dominant inheritance has been considered in some cases. In one American Staffordshire Terrier diagnosed with MCE, a de novo nonsense mutation in the EXT2 gene was identified, providing evidence supporting a possible genetic basis for the disease.

However, a genetic alteration identified in a single case does not establish that all cases of MCE in dogs develop through the same genetic mechanism. Further research is needed to better understand the genetic causes of this condition.

Similar osteochondroma-like lesions have been reported in humans and various animal species. In cats, osteochondromatosis has been associated with feline leukemia virus (FeLV) and feline sarcoma virus (FSV) infections in some cases. These reported associations in cats should not be directly interpreted as the cause of MCE in dogs.

Pathophysiology and the Relationship with Bone Development

Multiple cartilaginous exostoses are benign proliferative bone lesions associated with endochondral ossification. Endochondral ossification is the biological process through which cartilage is gradually replaced by bone during skeletal development.

MCE lesions most commonly affect the limb bones, ribs, and vertebrae. Bones formed through intramembranous ossification have generally been reported to be unaffected in dogs.

The condition usually develops in young dogs that have not yet completed skeletal growth. Lesion growth typically slows or stops once skeletal maturity is reached.

However, not every lesion necessarily follows the same growth pattern. Continued growth after skeletal maturity, or renewed growth in a previously stable lesion, warrants further investigation.

Symptoms of Cartilaginous Exostoses in Dogs

The clinical signs of MCE vary depending on the number, size, and anatomical location of the lesions. Some dogs have no obvious symptoms, and the lesions may be discovered incidentally during diagnostic imaging. In other cases, pressure on surrounding tissues may cause clinical problems.

Possible signs include:

• Firm, palpable swellings over affected bones

• Pain or discomfort during movement

• Lameness and restricted mobility

• Reduced range of motion in affected joints

• Discomfort caused by pressure on surrounding soft tissues

• Neurological abnormalities when spinal lesions compress nervous tissue

These signs may also occur with other orthopedic and neoplastic conditions. Therefore, a physical examination alone may not always provide a definitive diagnosis.

A detailed orthopedic assessment by a veterinarian is particularly important when multiple bony projections are identified in a young dog.

How Are Osteochondromas and MCE Diagnosed in Dogs?

Diagnosis involves evaluating the dog's age, clinical signs, lesion location, and growth behavior.

Radiography

Radiography is one of the primary imaging methods used to identify bony projections. It helps assess the number and distribution of lesions and their relationship with the underlying bone.

Computed Tomography (CT)

Computed tomography provides detailed anatomical information, particularly for lesions located in complex regions. It can help determine the dimensions and precise location of lesions affecting the spine or structures close to surrounding tissues.

Histopathological Examination

Imaging findings may support the diagnosis, but histopathological examination may be necessary in selected cases to establish the nature of a lesion. Examination of a tissue sample can help distinguish benign osteochondroma-like lesions from other bone abnormalities.

The diagnostic approach should be tailored to the individual patient according to the clinical findings and characteristics of the lesions.

Risk of Malignant Transformation

Cartilaginous exostoses are generally considered benign lesions. Nevertheless, the possibility of malignant transformation should be considered in rare cases.

Continued growth after skeletal maturity, renewed enlargement of a previously stable lesion, or the development of new clinical signs warrants further evaluation.

These changes do not independently confirm malignancy. However, they may justify repeat diagnostic imaging and, when indicated, biopsy or histopathological examination.

Some sources report a malignant transformation rate of less than 5% in affected dogs. This figure should not be interpreted as a definitive risk estimate for every patient, as the reported rate may depend on the study population and the evidence available.

Treatment and Monitoring

Treatment for cartilaginous exostoses in dogs depends on lesion size, anatomical location, clinical signs, and the effects on surrounding tissues.

For some lesions that do not cause symptoms or show suspicious growth characteristics, monitoring under veterinary supervision may be sufficient.

Surgical removal may be considered when lesions cause pain, restricted movement, compression of nervous tissue, or other significant complications. The decision to perform surgery depends on the anatomical location, the condition of surrounding structures, and the potential risks of the procedure.

Lesions that continue to grow or undergo structural changes after skeletal maturity should be reassessed for possible malignant transformation.

Conclusion

Multiple cartilaginous exostoses in dogs are benign bone lesions that commonly develop in young animals and produce cartilage-capped bony projections. A single lesion is generally called an osteochondroma, whereas multiple lesions are classified as multiple cartilaginous exostoses (MCE).

Although genetic factors may contribute to the development of this condition, its exact causes remain incompletely understood. Diagnosis and monitoring involve clinical examination, diagnostic imaging, and histopathological evaluation when necessary.

Most lesions exhibit benign behavior, but continued or renewed growth after skeletal maturity warrants further investigation. Appropriate veterinary assessment helps monitor disease progression and determine whether treatment is necessary.

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