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Degenerative Myelopathy (Hind Quarter Paralysis)
Aka Hind End Degeneration (HED)
Degenerative Myelopathy is an autoimmune disease. The Rats immune system attacks some parts of its body. Early signs of this illness are often misdiagnosed as arthritis.
Degenerative Myelopathy is similar to Multiple Sclerosis in humans. In Degenerative Myelopathy the myelin and axons are attacked.
In most cases it happens with Rats between the age of 18 months and 2 years who develop spinal nerve root degeneration and associated muscle degeneration, leading to clinical signs of posterior paresis, paralysis and incoordination.
Degenerative Myelopathy begins in the spinal cord and also affects other areas of the central nervous system, including the brain stem and sub-cortical white matter of the brain. The cause is most likely a combination of inherited weakness, plus environmental and toxic factors that lead to its development.
A young healthy Rat will walk on the front part of its feet, with its tail held off the ground. Early signs of mobility & flexibility loss are a tendency to walk flat footed. This does not affect the Rats gait or its ability to keep up with other Rats. The Rats tail will tend to drag on the ground as the condition progresses.
As the degeneration progresses there will be increased difficulty moving the back legs. The toes will tend to curve in and there will also be difficulty in standing unsupported on the hind legs. Climbing is also difficult and will become more so, resulting in frequent falls which may lead to more injuries in the Rat.
It is currently unknown if the Rat is aware of the progressive weakness because they continue to attempt climbing. All items that encourage climbing in the cage should be removed to avoid other injuries. If your Rat is living in a tall cage it is best to house it in a lower area with no levels to climb up or on.
Although Rats are social animals and prefer to live in groups, consideration must nevertheless be given to placing a Rat suffering with Degenerative Myelopathy in a cage on its own, to prevent injuries from its cage mates and allow the Rat to gain full access to food and water. Most bonded groups will accept the decreased mobility of a cage mate and will care for the disabled rat by snuggling and keeping them company. In cases where you see bullying and undesired behavior from the group, where the disabled animal may get injured, it is sometimes best to move the disabled animal into their own cage with a calm rat to keep them company.
Rats with paralysis from spinal degeneration are also at risk of bladder infections. In some cases the bladder does not empty properly, depending on the nerve involvement.
As the Rat drags itself on its hind legs it may develop calluses and sores on its legs. The Rat is likely to develop urine scalding. The paralysed Rat is unable to move itself out of the urine & faeces, regular warm soap and water will be required to minimise damage to the Rats skin from ammonia burns. The Rat should be checked regularly for foul smelling or bloody urine.
Paralysed Rats are also at an increased risk of getting pneumonia.
Rats that have Degenerative Myelopathy can be kept comfortable by placing them on clean soft bedding.
Some Rats will also have difficulty with their front feet/hands also resulting in not being able to hold its own food very well. If a Rat is unable to balance itself on its hind quarters and uses its front legs to support its weight, it is then unable to grasp and hold food. Food will need to be placed in front of the Rat on a flat surface. The food may also need to be of a softer diet so it is easier for the animal to eat. Hand feeding may also be helpful. The water bottle should also be placed close to the Rat so that the Rat does not need to move to be able to drink.
Toenails may need to be trimmed as the Rat no longer is able to wear them down naturally.
Rats generally have a lot of wax build up in their ears which is normally removed by the rat using its hind leg to scratch inside the ear, but a paralysed Rat is unable to this. The wax needs to be removed at least once a week with a cotton bud. If the wax is not removed regularly, solid material from the cage may also accumulate inside the ear and lead to a bad smell and an infection.
Unfortunately conventional medicine has very little to offer Rats with Degenerative Myelopathy. Some vitamins and selected drugs have delayed or prevented progress of degenerative Myelopathy in many Rats. While these treatments are aimed at suppressing the clinical signs, little has been done to prevent the development of this autoimmune disease.
The use of non-steroidal, anti-inflammatory drugs are generally used to treat the symptoms of degenerative Myelopathy however these medications have side effects including gastrointestinal upset, headaches, dizziness and ringing in the ears. One side effect that rarely is mentioned however is the inhibition of cartilage repair. This accelerates cartilage destruction and worsens the condition.
Degenerative Myelopathy is a very complex disease with many varying factors and causes. It is unlikely any one medication will ever be universally effective, however there are products that show great promise for providing long term relief and possibly even some reversal of this disease. Acupuncture can be tried with a knowledgeable vet as it has shown to help Degenerative Myelopathy temporarily. A Rat can live with Degenerative Mylopathy and still have a reasonable quality of life but you need to continue to be aware of the effects and issues that could occur with a Rat suffering from this ailment.