degenerative myelopathy

Pug Myelopathies

Did you know that Pugs are commonly diagnosed with T3-L3 myelopathies? There are so many to chose from I thought I'd take this TidBit Tuesday and discuss some of the more common ones. 


Intervertebral disc herniation

Dis herniation is a common etiology of a T3-L3 myelopathy in many dogs, and Pugs are no exception. Type I and Type II disc herniations have been diagnosed in Pug dogs in the thoracolumbar region. Clinical signs include acute (or chronic if type II) variably painful (but often WITH signs of discomfort in this breed), pelvic limb proprioceptive ataxia followed by paraparesis. Signs can progress to paraplegia with loss of deep pain. Surgical and medical correction have been shown to be useful for Pug dogs and depend on the severity of the clinical signs.


Subarachnoid diverticulum

Subarachnoid diverticulum (SAD) can be described as cystic accumulations of fluid in the subarachnoid space around the spinal cord. Pugs are cited as among the most common breeds to be diagnosed with SAD. Clinical signs are slow in onset and often include incontinence early in the clinical course. Dogs with SAD are not typically painful. Medical and surgical management have been tried however neither approach appears to be an overwhelming success. Medical management is typically my preferred approach. 


Meningomyelitis and Neoplasia

Any and all breeds are at risk for these two diseases and Pugs are not overrepresented in this group. That said, clinical signs would include acute or chronic onset of signs with paraparesis and proprioceptive ataxia in the pelvic limbs. Treatment is medical for meningoencephalitis and medical, surgical or with radiation therapy for neoplasia. 


Degenerative Myelopathy

Degenerative myelopathy (DM) is caused by a genetic predisposition to demyelination of the T3-L3 spinal cord segments. Pugs are over represented and either confirmed or strongly suspected to have a mutation of the SOD1 gene (I cannot remember if it has been confirmed, yet!), like  German Shepherd dogs. Clinical signs include a slowly progressive, non-painful, proprioceptive ataxia that progresses to paraparesis, then paraplegia. If not euthanized, pets can progress to tetraparesis and eventually respiratory failure. A diagnosis is made through findings of a normal MRI and CSF analysis along with appropriate clinical signs. Genetic testing can be useful but isn't a stand alone test. 


Constrictive myelopathy

This is the new kid on the block. First published several years ago, constrictive myelopathy is caused by a fibrous band of tissue that circles the spinal cord and causes a constriction to CSF flow and compression of spinal cord tracts. Constrictive myelopathy is now thought to form due to a lack of development (hypoplasia) of the articular processes of the TL vertebra. If you imagine the articular processes are the "hands" that hold the vertebra together, supported by muscles and ligaments, becomes easy to see how hypoplastic articular processes might result in vertebral instability. This instability would then result in fibrotic tissue forming to help "stabilize" the joint. Sadly, this fibrous tissue then causes spinal cord constriction. To make matters worse, SAD can also form secondary to chronic spinal cord trauma so these poor dogs can have constrictive myelopathy secondary to hypoplastic facets and SAD in their T3-L3 spinal cord segments. Yikes. A diagnosis is made on MRI. A recent study (https://onlinelibrary.wiley.com/doi/full/10.1111/jvim.16639?) evaluated the incidence of constrictive myelopathy alone, or in combination with other spinal cord diseases in a group of Pug dogs. They found only constrictive myelopathy in 3 dogs, constrictive myelopathy combined with IVDH in 17 dogs and IVDH only in 9 dogs, IVDH + SAD in 2 dogs and articular process dysplasia in ALL 32 dogs!

Summary:
Pug dogs are at risk for many causes of paraparesis and proprioceptive ataxia. A detail neurologic examination, history , and appropriate diagnostic imaging and spinal tap can help determine the underlying etiology and subsequently direct treatment most specifically. 

I hope this TidBit doesn't give you the impression that I am anti-Pug - I adore these little dogs. BUT,  I recognize their predisposition to specific spinal cord diseases when assessing them clinically. Remember, not all dogs with pelvic limb weakness have a disc herniation! 
Have a great week!