Degenerative Myelopathy (DM)

Degenerative myelopathy is a progressive neurodegenerative disease of the spinal cord affecting the white matter - the nerve tracts that carry signals between the brain and the limbs. It typically begins in the thoracolumbar region and progresses slowly forward along the spinal cord.

The cause is a mutation in the SOD1 gene. Dogs homozygous for the mutation (two copies, called "At Risk") are susceptible to developing DM. Importantly, not all dogs with two copies of the mutation develop the disease - penetrance is incomplete - and the mutation is very common in some breeds (nearly universal in certain Welsh Corgi populations).

DM typically affects dogs over eight years of age. It progresses slowly over months to years.

Progression stages

DM progresses predictably through stages:

Stage 1: Mild hindlimb ataxia (wobbling) and weakness. Difficulty on slippery surfaces. Some toe-dragging.

Stage 2: Moderate hindlimb weakness. Increasing ataxia. Clear lameness. Difficulty rising.

Stage 3: Paraplegia - inability to walk independently. The dog can still have normal bladder and bowel function initially.

Stage 4: Paraplegia with urinary and faecal incontinence.

Stage 5 (late): Progressive involvement of forelimbs and eventually respiratory muscles.

Progression from Stage 1 to paraplegia typically takes 6–18 months. With intensive physiotherapy, some dogs are maintained with ambulatory function for longer.

Weekly monitoring

For a dog with DM diagnosis, assess and log weekly:

• Hindlimb strength: Can they bear full weight? Partial weight? Not at all?
• Ataxia: Wobbling, crossing feet, swaying
• Toe-dragging/knuckling: Note which feet and how frequently
• Rising from rest: Independent, with some help, or not possible
• Balance: Can they stand with feet placed normally, or do they need continuous support?
• Bladder function: Urinating voluntarily and controlling timing? Starting to leak?
• Bowel function: Normal or incontinent?
• Muscle mass: Assess hindquarters - atrophy is progressive

Photograph a short walk weekly from behind - the progression is often more visible on video than in a daily examination.

Distinguishing DM from other causes of hindlimb weakness

DM must be distinguished from:

• IVDD (disc disease): Acute onset; painful; may have detectable spinal pain on examination. DM is gradual and classically non-painful.
• Hip dysplasia and arthritis: Pain is usually evident; X-ray findings clarify.
• Spinal tumours: Can look similar; MRI is required to differentiate.

The definitive diagnosis of DM requires MRI and CSF analysis to rule out other causes, plus post-mortem spinal cord histopathology for confirmation. In practice, a dog with compatible clinical signs, appropriate breed, and DM mutation status is often managed as presumptive DM.

Physiotherapy and supportive care

While there is no treatment that stops DM progression, intensive physiotherapy significantly slows functional decline:

• Hydrotherapy: Supports body weight in water allowing limb movement; maintains muscle mass and joint mobility
• Assisted walking: Walking harnesses (rear-support harnesses like Help 'Em Up) that support the hindquarters allow the dog to continue walking as weakness progresses
• Wheelchairs: Rear-wheel carts when walking ability is lost - most dogs adapt remarkably well
• Passive range of motion exercises: Maintain joint mobility as voluntary movement declines
• Pressure sore prevention: A paralysed dog cannot shift their weight; appropriate bedding and regular repositioning prevent sores

Bladder and bowel management

As the disease progresses to incontinence:

• Urinary management: Frequent opportunities to urinate; some dogs require manual bladder expression (the vet will teach you how)
• Hygiene: Keep the perineal area clean and dry to prevent skin scalding and infection

When to contact your vet

Contact your vet soon if:

• Hindlimb weakness develops in an older German Shepherd, Corgi, or other at-risk breed
• A known DM dog shows rapid deterioration that seems faster than the typical pace (IVDD can complicate DM)
• Bladder function is changing

Schedule a routine appointment for:

• Regular physiotherapy referral reviews
• Assessment of quality of life as the disease progresses

Frequently Asked Questions

Is DM painful? DM itself is classically non-painful - the demyelination prevents sensory signals from reaching the brain. Dogs often seem comfortable and engaged despite significant physical impairment. This is both a characteristic of the disease and a reason why quality of life often remains good for longer than owners might expect.

My dog has tested "At Risk" for DM but has no symptoms. What should I do? "At Risk" means susceptibility, not certainty. Monitor for early signs of hindlimb weakness or ataxia from around age seven to eight. Begin physiotherapy early when signs appear - earlier intervention gives more time with good function.

How do I know when quality of life is no longer adequate? Quality of life frameworks (such as the HHHHHMM scale - Hurt, Hunger, Hydration, Hygiene, Happiness, Mobility, More good days than bad) can help structure this assessment. A DM dog who is mentally engaged, not in pain, eating well, and whose physical care needs are being met may have good quality of life even in a wheelchair. When physical care becomes overwhelming or the dog loses mental engagement, discussing end-of-life with your vet is appropriate.

Will my dog's forelimbs be affected? In the later stages of DM, the degeneration does progress to involve the thoracic spinal cord and eventually forelimb function. This stage takes years in most dogs. The majority of DM dogs reach a quality-of-life decision point before forelimb involvement becomes significant.

My Corgi is 6 - should I DNA test now? If you haven't already, yes. Knowing the result in advance doesn't change the outcome but allows you to plan, begin physiotherapy resources early, and monitor actively from the appropriate age. Results in the "At Risk" category in a young dog also inform breeding decisions.