Presentation
6 month history of progressive generalized ataxia. C1-C5 myelopathy.
Patient Data
There is collapse of multiple intervertebral disc spaces with gas cavitation. The epiphyses of affected spaces are misshapen with proliferative new bone and medullary sclerosis. The associated intervertebral discs are mildly herniated. There is moderate herniation at L4-5, L6-7, and L7-S1 right sided with a component of osseous proliferation contributing to the compression.
The bone quality is variable with the dorsal lamina and spinous process appearing sclerotic and the vertebral bodies intermittently decreased in density. The facet joints from T10-L7 are asymmetric and malformed.
The left sacroiliac joint is asymmetric due to transitional vertebrae, and has both internal sclerosis and irregularity and lysis with soft tissue replacement of the medial cortex.
The right tympanic bulla is thickened and there is bilateral soft tissue filling of the tympanic cavities.
There is multifocal loss of T2 signal intensity of the intervertebral discs. There is a site of spinal cord compression and T2 hyperintensity at C2-3 caused by a combination of spinal canal narrowing, facet hypertrophy, and mild intervertebral disc protrusion. The C3 vertebral body is misshapen causing a dorsal protrusion at the cranial endplate. The right nerve root is enlarged and contrast enhancing.
There is an additional site of stenosis at C1-2 with circumferential compression of the spinal cord and mild enlargement and dorsal deviation of the nerve roots. These nerve roots are contrast enhancing and visible to the level of the internal carotid artery.
The C3-4 and C5-6 discs are mildly protruding without significant compression.
Multiple vertebral anomalies with epiphyseal dysplasia, resulting in spinal cord compression and neuritis at C1-2 and C2-3. Mild spinal cord compression at L4-5, L6-7, and L7-S1 primarily from osseous proliferation with mild disc herniation. The underlying cause of these changes may be developmental or metabolic such as a lysosomal storage disease, and do not appear to be inflammatory.
The degenerative change of the left sacroiliac joint is likely secondary to the transitional vertebra. Incidental otitis media.
Case Discussion
Mucopolysaccharoidosis is a lysosomal storage disease. There are several types with varying severity, however musculoskeletal anomalies including epiphyseal dysplasia are distinguishing features. Cerebrospinal fluid was collected and showed elevated protein as well as macrophages, many of which contained numerous variably sized, metachromatic granules consistent with Alder-Reilly bodies.These granules are characteristic of mucopolysaccharoidosis and provided evidence of the likely diagnosis of MPS I. Additional clinical findings were corneal opacities which are also caused by the storage disease. A case report of two Boston Terriers with MPS I was supportive of the diagnosis.
MPS 1 is a rare genetic disorder in dogs caused by deficiency in alpha-L-iduronidase. The glycosaminoglycans then accumulate in various tissues of the body. Musculoskeletal changes include joint effusion and degenerative change, narrowed intervertebral disc spaces and vertebral lysis. A genetic mutation has been identified in the Boston Terrier, possibly related to selection for unusual coat colors (chocolate brown,dilute chocolate brown). This dog had the diluted coat color. A PCR test was performed but did not produce results.
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