Causes and management of decreased mobility in old dogs (Proceedings)

As dogs get older they frequently "slow up". This is to be expected and as a result it is common that such animals do not receive a careful evaluation and a presumptive diagnosis of "arthritis" or "old age" is made. The situation is further complicated by the fact that older animals tend to have multiple problems, and determining which is most significant can pose a diagnostic and therapeutic dilemma. The aim of this presentation is to describe a useful approach to older dogs that are becoming less mobile, and to discuss common differential diagnoses, their treatment and prognosis. Case examples will be used.

Differential diagnosis

The most common complaint from owners is that their dogs have chronic pelvic limb weakness, although in some cases, all four legs are affected. Important differential diagnoses for pelvic limb weakness include:

• Degenerative joint disease of the hips, stifles and tarsi,

• Degenerative lumbosacral disease,

• Compressive thoracolumbar spinal cord disease as a result of type II disc herniations of the thoracolumbar spine or neoplasia.

• Degenerative spine cord disease (degenerative myelopathy)

• Diskospondylitis.

• Degenerative joint disease of the articular facets of the TL spine can cause pain and stiffness.

• In rare instances, early signs of compressive cervical spinal cord disease can manifest as pelvic limb weakness.

• Peripheral neuropathies affecting the sciatic nerves should also be considered

• Animals suffering from any severe systemic illness may be weak.

Similar differentials apply when all four limbs are affected, namely, degenerative joint disease, compressive cervical spinal cord disease including "wobbler syndrome" in all of its forms, diskospondylitis, peripheral neuropathies and systemic illness. It is also important to remember that brain stem disease can cause weakness in thoracic and pelvic limbs, although it is usual to detect some other evidence of brain stem involvement (e.g. cranial nerve deficits) in these patients.

Patient assessment

Detecting lameness in one limb does not pose a problem for veterinary practitioners, but if more than one limb is involved it becomes more difficult to assess. If unsure whether more than one limb is involved, each limb in turn can be held in flexion for approximately 20-30 seconds and then the animal encouraged to walk immediately the limb is released (a flexion test). This may highlight subtle abnormalities. As a general rule neurologic diseases do not cause lameness, but the exception occurs when a nerve root is compressed. Compression of a nerve root causes the animal to favor that limb in an attempt to relieve pressure on the nerve root. Dogs with thoracolumbar spinal cord disease have an ataxic and paretic pelvic limb gait. The foot may be scuffed on protraction or in more severe disease, overt knuckling may be The initial physical evaluation of the patient should be performed very carefully to distinguish between orthopedic and neurologic disease and to localize any neurologic deficits. As orthopedic and neurologic disease coexist in many older dogs, and an attempt should therefore be made to determine the clinical severity of any pathology present. An accurate history should be taken to generate a clear picture of the owner's complaint. It is important to determine whether the signs are worse first thing in the morning, improve with mild exercise, but are worse subsequent to this, as this suggests degenerative joint disease is playing a role. Neurologic diseases tend to cause signs that are present the whole time and are unaffected by rest or exercise. After completing a general physical examination, the patient's ability to rise from a sitting position and its gait should be evaluated. Dogs with arthritis usually walk better as they continue to move. present. Crossing the feet, staggering, and incorrect foot placement when circling or negotiating steps all suggest neurologic disease. Involvement of the thoracic limbs may be obvious in cervical spinal cord disease, but sometimes is subtle. In caudal cervical spinal cord lesions, dogs may have a short, stilted or even lame thoracic limb gait with atrophy of muscles over the scapulae. Wheelbarrowing the animal may highlight thoracic limb weakness. Subtle proprioceptive deficits can be identified from worn nails.

Following gait evaluation a careful orthopedic and neurologic examination should be completed. In general it is useful to complete the orthopedic examination first as orthopedic disease may alter the findings of the neurological examination. For example, in dogs with severe and chronic changes in their stifles as a result of anterior cruciate ligament rupture it may not be possible to elicit a patellar reflex. When performing the critical test of conscious proprioception (placing the paw on its dorsal surface), it is important to support the dogs weight slightly so that they can shift weight to replace their foot easily. They may be reluctant to do this if they have severe orthopedic disease, leading to incorrect conclusions about their examination. The presence of conscious proprioceptive deficits clearly indicates that there are neurological deficits. It is also important to look for several lines of evidence to support any conclusions drawn. For example, older dogs are may have absence of patellar reflexes (assesses the femoral nerve) as an incidental finding with no evidence of orthopedic or neurologic disease.1 Thus, the clinical significance of absence of a patellar reflex is gauged by looking for other signs associated with damage to the femoral nerve such as obvious paresis and ataxia of the affected leg, and atrophy of the quadriceps muscle. Assessment of the sciatic nerve is most reliably achieved by extending the pelvic limb completely, especially the hock, and performing a withdrawal reflex while maintaining some resistance to flexion of the limb and watching for hock flexion. The femoral nerve innervates the hip flexors and so the presence of hip flexion does not indicate intact sciatic function. If a peripheral neuropathy is suspected, the larynx should be ausculted to detect inspiratory stridor, indicative of laryngeal paralysis. The recurrent laryngeal and sciatic nerves are the longest peripheral nerves in the body and therefore likely to affected first in peripheral neuropathies. The spine should be manipulated and palpated for evidence of pain with particular attention paid to the lumbosacral junction. In order to be considered a solid finding, any pain elicited should be repeatable. Distinguishing clinical features of the common differential diagnoses, appropriate means of treatment and prognosis are described below.

Degeneratibe lumbosacral disease

Degenerative lumbosacral (LS) disease is the term used to describe compression of the nerve roots of the cauda equina at the level of the LS junction as a result of degenerative changes. Common changes present include disc protrusion, new bone formation around the LS foraminae, hypertrophy of the synovial membranes of the articular facets with degenerative joint disease of the facets, and instability. Any or all of these processes can be present. Classic signs displayed by dogs with LS disease in the early phases include difficulty rising or jumping up onto things, a stiff stilted pelvic limb gait that can be associated with lameness and therefore be confused with orthopedic disease, LS pain (this is probably the most reliable sign of LS disease). As the disease progresses the owners note that tail carriage changes (you usually need to ask owners about this specifically), pelvic limb CP deficits and ataxia may develop along with muscle atrophy and eventually fecal and urinary incontinence. LS disease is probably much more common in older large breed dogs than realized. Diagnosis is made by computed tomographic (CT) or magnetic resonance (MR) imaging of the LS region, but any imaging findings must be supported by clinical evidence of disease, as some animals can appear to have severe compression of nerve roots on images but have no associated signs. Survey radiographs of the area usually show degenerative changes such as spondylosis but cannot be used to definitively diagnose the condition. Treatment is surgical or conservative although little is known about the success of conservative management. Conservative management includes pain control with anti-inflammatory drugs and muscle relaxants, and controlled exercise on flat surfaces. Alternatively, surgical decompression and sometimes stabilization can be achieved by performing a dorsal laminectomy and fenestrating the LS disc. Surgical outcomes are good in dogs with pain and mild neurological deficits2 but the prognosis is worse if incontinence is present.

Type I intervertebral disc disease

Hypertrophy and bulging of the annulus fibrosis is termed type II disc herniation and tends to occur at the more mobile regions of the spine (caudal cervical, thoracolumbar and LS) in both large and small breeds of dog. It causes chronic progressive compression of the spinal cord and plays a role in both caudal cervical spondylomyelopathy (wobbler syndrome) and degenerative LS disease. Signs of progressive myelopathy including ataxia, paresis and conscious proprioceptive deficits related to the site of compression develop and may suddenly worsen in some dogs. Diagnosis is reached by myelography or MRI, and again the radiographic findings have to be correlated with the clinical signs as many animals will show multiple sites of compression. Treatment options include conservative management with anti-inflammatory drugs (a low dose of a corticosteroid may be helpful in some cases) combined with a physical therapy program. Again it is very unclear how successful this is but in cases that are not good anesthetic risks, when signs are mild and only slowly progressive, or when multiple sites of severe compression are evident on the imaging study, this approach may be the best option. More aggressive management centers on surgical decompression, and in some cases stabilization. As a general rule, surgery to remove type II disc herniations in the thoracolumbar region carries more risk of causing neurological deficits than removal of an acute type I disc herniation. This is because the disc is often intimately associated with the spinal cord, and the amount of cord damage that has already occurred as a result of this slow progressive process is much greater. Surgery is recommended when the animal shows severe signs (paraparetic or worse), or the signs are progressing obviously. It is always better to perform surgery prior to the animal losing the ability to walk.

Spinal neoplasia

The most common type of neoplasia affecting the spinal cord is vertebral sarcomas. These tumors cause pain and progressive neurologic signs associated with the location of spinal cord compression. In many instances they can be diagnosed from plain radiographs as an area of bone lysis and proliferation. Definitive diagnosis is reached by biopsy of the mass and CT or MR imaging provides greater detail of the lesion for treatment planning. In general, these tumors carry an extremely poor prognosis3: surgical decompression can be attempted in animals that still retain voluntary motor function, and radiation may slow tumor progression. In animals with severe pain, palliative radiation can be a very effective means of providing good quality of life for a limited period. The use of corticosteroids at anti-inflammatory doses can produce a short lived but dramatic improvement because of the effect on peritumoral edema. Indeed, if an owner of a paraparetic old dog has declined further work up and a dose of prednisone produces a dramatic improvement, neoplasia should be considered as a strong differential. Other tumors that can cause bone lesions visible on survey spinal radiographs include multiple myeloma and plasma cell tumors4. These tumors are responsive to chemotherapy and treatment should be considered for such cases. Meningiomas can also cause compression of the spinal cord, diagnosed by myelography or MR imaging. These tumors are responsive to surgery with or without radiation if treated early in the course of the disease prior to onset of severe neurological deficits. Finally, nerve root tumors and other forms of intramedullary tumor can occur. In general, intramedullary spinal cord neoplasia carries a poor prognosis. Nerve root tumors can be treated successfully by amputation of the affected limb if adequate margins can be achieved. Unfortunately, in many instances the tumor is located too proximally on the nerve root and has spread along multiple nerves of the brachial or LS intumesences, making adequate removal impossible. As a general rule, the earlier spinal neoplasia is diagnosed, the greater the chance of it being treatable.

Degenerative myelopathy

Degenerative myelopathy is a slowly progressive disease of the spinal cord and lower motor neurons, with the thoracolumbar region predominantly affected. It is now known to affect many breeds but German Shepherd dogs, Pembroke Corgis, Chesapeake Bay Retrievers and Boxers are over-represented. Diagnosis is established by ruling out a compressive or inflammatory disease and testing positive on the genetic test available for the superoxide dismutase mutation associated with the disease. Treatment centers around providing a balanced diet rich in anti-oxidants and keeping the animal mobile. Clinically these dogs remain continent even when severely affected and so the development of incontinence should cause suspicion that there is another process occurring.

Diskospondylitis

Although infection of an intervertebral disc and its associated vertebral endplates is classically a disease of young intact large breed dogs, any dog can develop diskospondylitis, particularly if they have concurrent predisposing factors such as prostatic disease or diabetes. Clinical signs include spinal pain (although it is not always evident) and myelopathy relating to the site of the lesion. Sudden exacerbations can occur due to pathologic vertebral fractures. The diagnosis is typically made from survey spinal radiographs (lysis and sclerosis of adjacent vertebral endplates). Urine should be cultured routinely and blood cultures can be performed if possible. Brucella titers should be measured. Most dogs respond well to prolonged courses of broad spectrum antibiotics although some have antibiotic resistant infections or fungal infections and others need surgical decompression and stabilization.

Peripheral neuropathies

Peripheral neuropathies can occur as a paraneoplastic disease (e.g. in dogs with insulinoma), as a component of metabolic or endocrine diseases, as degenerative processes in aging dogs or as a result of inflammatory disease.5 Frequently the sciatic and recurrent laryngeal nerves are affected first, causing stridor and difficulty rising. Diagnosis requires electrophysiological evaluation and nerve and muscle biopsies. Treatment and prognosis obviously depend on the underlying cause.

Summary

It is important to perform careful orthopedic and neurologic examinations on older paretic dogs, and to ensure that good quality survey spinal radiographs are obtained. This should help to identify treatable disease such as diskospondylitis early on, and screens for diseases with a poor prognosis such as vertebral sarcomas. Any owner interested in determining a definitive diagnosis should be offered further evaluation and imaging in order to identify treatable neoplasms early in their clinical course. For owners not interested in spinal surgery, once diseases such as diskospondylitis have been ruled out, treatment with anti-inflammatory drugs and physical therapy should be initiated.

References

Levine JM, et al., J Vet Intern Med. 2002; 16: 244-6.

De Risio L, et al., J Am Vet Med Assoc. 2001; 219: 624-8.

Dernell WS, et al., J Am Anim Hosp Assoc. 2000; 36: 245-51

Rusbridge C, et al., J Vet Intern Med. 1999; 13: 126-33.

Cuddon PA. Vet Clin North Am Small Anim Pract. 2002;32:207-49.

Key words: lumbosacral disease, vertebral neoplasia, type II disc diseases, peripheral neuropathy