Vets are commonly presented with a pet that has hind limb weakness. Sometimes this occurs suddenly and is very obvious. In some circumstances, the changes come on slowly and may only be noticed by the vet during routine examination. This is especially common in older pets where hind limb weakness is seen as part of ageing and often perceived to be ‘normal’ by the owners. These pets may be reluctant or unable to do things they used to (jump on the bed/sofa, leap up retaining walls), be slowing down on walks, or have difficulty rising.
When a pet presents with hind limb weakness, whether acute or chronic, a thorough history of the problem will be taken. This includes vaccination status, travel history (particularly in the eastern states of Australia where paralysis ticks are endemic), diet and supplements, previous surgeries or illnesses, medications or possible toxins. Speed of onset of symptoms is pertinent. In rapid onset, a toxin may be suspected, whereas a gradual development of symptoms suggests a chronic disease of some form.
As well as physical examination of all the limbs, the movement of limbs and joints are assessed at various walking speeds. Your vet will check to see if the pet is trying to carry more weight on the front limbs (more likely with bone or joint pain than true weakness) or if there is a ‘hip hike’ on one side. They'd also do a full physical examination looking for a systemic (body-wide) cause of the weakness, as well as a neurological assessment, checking reflexes, muscle tone and whether your pet knows where his feet are all the time. Your vet will need to assess whether the weakness is due to an orthopaedic (bone) or joint problem, a neurological (nerve) problem, a muscle problem or a metabolic problem.
Overall, the following conditions are just some that appear as hind limb weakness: hip dysplasia, hip arthritis, knee arthritis, knee ligament rupture, spinal arthritis, pelvic or spinal trauma, spinal cord disease, snake bite, tick paralysis, metabolic disturbances, anaemia, low blood oxygen, and disease of the junctions between nerve and muscle.
In many dogs, chronic, bilateral (both sides) arthritis of the hips or knees will present as weakness. Sometimes a trial of arthritis medication will clarify the diagnosis. However, if the cause of weakness is uncertain, further tests may be suggested. These may include blood tests and x-rays or more advanced imaging such as contrast x-rays, CT or MRI scans where available. In emergency cases of hind limb weakness, diagnosis may come second to emergency therapy. If snakebite or tick paralysis (a regionally variable risk) is suspected, urgent treatment is required.
If your pet develops signs of weakness in the back legs, either gradually or suddenly, a thorough examination by your vet as soon as possible is advisable for diagnosis and appropriate treatment.