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Orthopaedic Conditions in Geriatric Cats

Philip Witte, BSc, BVSc, MRCVS. Harry Scott, BVSc, Cert SAD, CBiol, MIBiol, DSAS (Orth), FRCVS - 18/09/2011

Orthopaedic Conditions in Geriatric Cats

 Philip Witte, BSc, BVSc, MRCVS
 Harry Scott, BVSc, Cert SAD, CBiol, MIBiol, DSAS (Orth), FRCVS

Introduction

Age is frequently a diagnostic pointer in small animal disease. Cats live longer and the disease patterns in our feline patients are changing. When presented with an older cat that shows evidence of a musculoskeletal disorder, the clinician should consider conditions that have a tendency to be specific to this age-group of patients as well as more universal problems; this article offers an overview on some of the most common problems encountered in geriatric patients.

Degenerative joint disease

Degenerative joint disease (DJD) is a general descriptive term for degenerative changes occurring in any type of articulation. Figure 1Osteoarthritis (OA) is a specific type of DJD that affects diarthrodial synovial articulations. It is characterized by deterioration of articular cartilage, osteophyte formation, bone remodeling, changes in peri-articular tissues and low-grade non-purulent inflammation. Feline DJD is common. Figure 2In one study 90% of a hospital’s feline population showed evidence of DJD in one or more joints (1). In the past OA has been overlooked as a cause of morbidity in cats but recent evidence suggests that the disease is more prevalent than previously presumed (2). In cats overt lameness is not the most significant clinical sign of OA and radiographic severity often correlates poorly with clinical signs. In one study only 33% of cats with OA showed obvious lameness (3).Figure3 Cats are less demonstrative than dogs in indicating that they are in pain, and resentment to handling, aggression and lack of responsiveness to human attention may be the most obvious manifestations of both acute and chronic pain.Figure4 Radiography should be performed in geriatric cats where these clinical signs are observed. Radiographic signs of OA include osteophytes, enthesiophytes, subchondral bone sclerosis, bone remodeling, soft tissue mineralization (intra-articular, capsular or extra-articular), joint capsule thickening and soft tissue swelling (Figures 1-4). Entheses are the osseous attachment sites of tendons and ligaments; pathology at these sites is known as enthesiopathy and generally results in the formation of enthesiophytes. Figure5In the spine enthesiophytes are termed spondylosis deformans (see below). Degenerative enthesiopathy may accompany OA and other joint disorders such as synovial osteochondromatosis (Figure 5) but its sole presence is not indicative of OA and enthesiophytes may be seen in elderly cats as an incidental finding.

Treatment options include the usual triad of conservative management (body weight restriction, exercise modulation and medical therapy), and salvage surgeries. Surgical options include femoral head and neck osteotomy or total hip replacement to address lameness associated with coxofemoral osteoarthritis, or arthrodesis for some other joints. Cats tend to limit their own activity appropriately when they have painful joints (which may contribute to the late recognition of OA in this species), but management may include techniques such as feeding from the floor and providing steps up to favorite perches to minimize the amount of jumping required.

 Secondary hyperparathyroidism

Hyperparathyroidism is an overactivity of the parathyroid glands resulting in an excessive production of parathyroid hormone. Hyperparathyroidism leads to osteopenia and predisposes to pathological fracture (Figure 6). The condition most commonly occurs in geriatric cats secondary either to chronic kidney disease (renal secondary hyperparathyroidism) or hyperthyroidism (hyperthyroid-related hyperparathyroidism).
Figure 6No discussion of the elderly cat is complete without a mention of hyperthyroidism, as it is the most common endocrine disorder in the species. Hyperthyroid cats have a significant derangement of calcium metabolism with a variable degree of secondary hyperparathyroidism. Hyperthyroidism has also been shown to cause a severe reduction in bone density (thyroid hormones favor bone resorption) in humans which has been reported to lead to pathological fractures in untreated chronic cases (4). It may be prudent to perform serum biochemical testing and urinalysis to ascertain both renal and thyroid function in any elderly cat presented with a fracture, particularly where the bones appear osteopenic radiologically, prior to consideration of repair.

Treating hyperparathyroidism which is secondary to kidney dysfunction will include standard therapies for renal disease, whilst if hyperthyroidism is present treatment options include thyroid ablation using radioactive iodine, surgical thyroidectomy and medical management with anti-thyroid drugs (5). Bone mineral density improves following treatment in humans (4), and appropriate therapy of hyperthyroidism may be expected to result in a reduction in the risk of hyperparathyroidism-related fractures in cats.

Spondylosis deformans

Spondylosis of the feline vertebrae is most commonly seen in the thoracolumbar and lumbosacral regions of the spine of older cats (Figure 7). The pathogenesis is related to the formation of enthesiophytes associated with degeneration of the annulus fibrosus of the intervertebral disc. Figure 7Spondylosis deformans may be seen either as an incidental finding or may be associated with mild to moderate spinal pain. Spondylosis deformans on plain radiography in the presence of neurological dysfunction is an indication for more advanced imaging and should not be considered a diagnostic finding (Figure 8). Note that Hansen type I and II intervertebral disc disease has been reported in cats (6), and surgical management of these conditions has resulted in more favourable outcomes in cases in the literature (7).

 Figure 8

Thromboembolism

Aortic thromboembolism is one of the most common causes of hindlimb paresis and paraplegia in cats. It is usually secondary to cardiomyopathy and left atrial dilatation. Thrombi form in the dilated left atrium or auricle and fragments (emboli) break off and travel through the blood vessels, occluding the distal aorta at the level of the iliac arteries by formation of a “saddle thrombus” (Figure 9).Figure 9 - thromboemboli will commonly lodge at the aortic trifurcation ('saddle thrombus'), occluding the iliac arteries. thromboemboli may lodge at other sites Occasionally thromboemboli may lodge at other sites. The presence of the clot then triggers local vasoconstriction which further reduces circulation to the hindlimb. Ischemia leads to myopathy and neuropathy of the affected limbs. Reperfusion injury can occur when circulation returns and potentially fatal arrhythmias can result secondary to hyperkalemia. The typical presentation is peracute paraplegia, pain and dyspnea, which can mimic the signs seen in cats following unobserved pelvic/spinal and thoracic trauma resulting from a road traffic accident. Physical examination will confirm an absence of femoral pulses, cold distal limbs and cyanosed pads, firm hindlimb muscles, absence of deep pain perception, lack of anal tone and a distended bladder in severe cases. Signs of cardiac disease such as tachypnea, tachydysrhythmia, heart murmur and gallop sounds may also be evident. Serum biochemistry abnormalities include elevated muscle enzymes and lactate and various manifestations of poor renal perfusion. Treatment options are numerous (8) and in-depth discussion is outwith the scope of this review - the clinician is directed to current literature for full details. However options include immediate analgesia, oxygen supplementation, frusemide (if pulmonary edema is present) and intravenous fluid therapy to address hyper kalemia, renal hypoperfusion and cardiovascular shock. Therapy after the initial 6-12 hours involves vigilant monitoring of ECG, acidosis and potassium levels, with appropriately targeted medical treatment. Heart therapy may be required for congestive heart failure in the medium to long term and thromboembolism prophylaxis (aspirin, clopidogrel, low molecular weight heparin), all with unproven efficacy, may be administered to prevent the risk of future episodes.

Figure 10Neoplasia

Neoplasia of the skeletal system is uncommon in cats. Most bone tumors in cats are malignant, with osteosarcoma, chondrosarcoma Figure 11(most commonly arising from the mandible, proximal tibia and scapula) and fibrosarcoma being most common (9) (Figure 10). Treatment by aggressive surgery (such as amputation) can be curative in cases of primary bone neoplasia, though meticulous staging (local biopsy, thoracic radiography in three views, abdominal ultrasonography) should be performed prior to consideration of such a procedure.

  • Osteosarcoma accounts for 70-80% of all primary bone tumors, occurring in the hindlimbs more commonly, and particularly in the distal femur and proximal tibia. In the forelimbs the proximal humerus is the most common site. Radiographic appearance of osteosarcoma is often primarily lytic, particularly in long bones, although the aggressive, poorly delineated, destructive and locally invasive lesions more typical of the canine condition can be seen on occasion.Figure 12
  • Round cell tumors which affect bone in cats include plasmacytoma, multiple myeloma and lymphoma (commonly associated with FeLV).
  • Squamous cell carcinomas and synovial cell sarcomas may also invade bone. Diagnosis should be confirmed by biopsy using a bone-marrow biopsy needle.
  • Primary bronchogenic carcinoma in the cat has a predilection for metastasis to the digits (Figures 11-13). Indeed digital metastasis of pulmonary malignancies is not uncommon in the cat but has not been reported in the dog and is uncommon in humans (10). Typically cats present because of lameness associated with a lesion in one or more digits. Note that the lameness almost invariably precedes respiratory signs despite the presence of a radiographically detectable pulmonary mass. Amputation of a digit may be required to confirm the diagnosis but does little to alter the clinical course of the disease (11). All geriatric cats presented with painful digital swellings should have thoracic radiographs taken to check for a primary pulmonary neoplasm.

 

Figure 13

Conclusion

When faced with possible musculoskeletal problems, lameness, stiffness and weakness are common presenting signs with older cats; a thorough clinical examination, coupled with relevant diagnostic tests, should enable the veterinarian to work towards a definitive diagnosis. Age can be a diagnostic pointer in many of these conditions.

This article was kindly provided by Royal Canin, makers of Mobility diet for dogs and cats.  For the full range please visit www.RoyalCanin.co.uk or speak to your Veterinary Business Manager:

Royal Canin Mobility FelineRoyal Canin Mobility

 

References

1. Hardie EM, Roe SC, Martin FR. Radiographic evidence of degenerative joint disease in geriatric cats: 100 cases (1994-1997). J Am Vet Med Assoc 2002;220:628-632.
2. Clarke SP, Mellor D, Clements DN, et al. Prevalence of radiographic signs of degenerative joint disease in a hospital population of cats. Vet Record 2005; 157:793-799.
3. Godfrey DR. Osteoarthritis in cats: a retrospective radiological study. J Small Anim Pract 2005;46:425-429.
4. Vestegaard P, Mosekilde L. Hyperthyroidism, bone mineral and fracture risk - a meta-analysis. Thyroid 2003;13:585-593.
5. Mooney C. Decision making in the treatment for hyperthyroidism in cats. In Practice 1996;18:150-156.
6. King AS, Smith RN. Protrusion of the intervertebral disc in the cat. Vet Record 1958;70:509-515.
7. Marioni-Henry K. Feline Spinal Cord Diseases. Vet Clin Noth Am Small Anim Pract 2010;40:1011-1028.
8. Moise NS. Presentation and management of thromboembolism in cats. In Practice 2007;29:2-8.
9. Liu S, Dorfman HD. Primary and secondary bone tumours in the cat. J Small Anim Pract 1974;15:141-156.
10. Gottfried SD, Popovitch CA, Goldschmidt MH, et al. Metastatic digital carcinoma in the cat: a retrospective study of 36 cats (1992-1998). J Am Anim Hosp Assoc 2000;36:501-509.
11. Scott HW, McLaughlin RG. Miscellaneous orthopedic conditions. In: Scott HW, McLaughlin R, eds. Feline Orthopedics. London: Manson Publishing, 2007;335-350.

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