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7

Common Diseases

and Pathologies

Andy Mead and Julia Robertson

•Investigation of canine lameness

•Common joint diseases causing lameness

•Disorders of muscles and tendons

•Neoplasia

•Spinal disease

•Peripheral neurological disease

Investigation of canine lameness

The diagnosis of any lameness often presents a challenge. Diagnosis must be made by a qualified veterinary surgeon who, if unsure, will refer the case to an orthopaedic specialist. It is preferable that the primary cause of the lameness can be diagnosed and treated as early as possible in the disease process, as this will result in a more favourable prognosis. It is easier to make a diagnosis if the disease is more advanced, but this makes it more difficult to treat, and this will lead to a poorer prognosis.

Taking the history

One of the most important parts of the consultation and diagnostic process is taking a thorough history; this will precede the examination, which is also very important. This is true for both veterinarian and physiotherapist alike.

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The following questions should be put to the handler in order to obtain a thorough and accurate signalment and history:

•What is the dog’s signalment (age, breed, and sex)?

•How long has the owner owned the dog?

•How long have the clinical signs been present?

•Was there any traumatic event associated with the onset of lameness?

•Which limb or limbs are affected?

•Is the lameness worse at a particular time of day?

•Is it worse at particular times of year or in certain weather?

•Is there any change before or after exercise?

•Has the owner given any medication, or joint supplements, and did they help?

•Have any previous diagnoses been made?

The examination

In a case of lameness, the dog should be observed from afar to confirm the nature of the lameness, its severity, and to look for swelling, symmetry, or any obvious pathology. It is important that the clinician remains open-minded at this stage, as the owner’s perception of lameness cannot be guaranteed to be correct, nor should it be assumed to be complete. Also, the veterinarian must be careful to avoid focusing in on the obvious and miss the less obvious problems. If time allows, the patient should be observed in motion, if possible at the walk and trot, over different surfaces (both hard and soft ground), coming towards and going away from the observer, and moving on a circle. This approach is adopted from the world of equine medicine, to give clues as to the likely position of the lameness of a horse. Lameness that worsens on hard or uneven ground may be indicative of the site of

lameness being in the distal limb, whereas lameness that is worse on soft ground is more likely to be due to proximal limb problems, as the dog has to increase the range of motion of the upper limb.

Next, the whole of the dog is examined, but special attention is given to palpation of the affected limb/s. Palpation is possibly the single most important part of the physical examination of the dog. Touch provides information regarding heat, pain, swelling, joint effusion, and any notable differences between left and right. Thus, ‘normal’ anatomical features of the patient can be ruled out from being the cause of the pathology. Flexion and extension of the joints of the affected limb/s should be conducted, bearing in mind it is impossible to isolate all of the joints completely, such as the elbow and shoulder. Flexion of the elbow would result in some flexion of the shoulder, making it difficult to localize the affected area. Care should be taken, as the aim is not to exacerbate the condition, nor should the patient be aggravated. It should be remembered that different dogs will manifest discomfort in different ways. Salivation, a sideways glance, shifting weight onto different limbs, vocalizing, and obvious shows of aggression can all be indicative of pain.

Information gathered from the signalment (age, breed, and sex), history, and clinical examination can then be pieced together in order to form a tentative diagnosis, to direct further diagnostic procedures to confirm the suspected diagnosis, or to assist the commencement of appropriate therapy.

Diagnostic techniques

Sedation

It may be impossible to examine the fully conscious patient properly, due to the nature of the condition, or the inability to convince the patient to relax! Often,

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veterinarians will enlist the help of sedative drugs, or even induce general anaesthesia in order to fully manipulate the limbs and joints. This allows a more thorough examination of the dog, and removes the inherent stabilization of joints provided by the larger muscle groups. One example of a technique of manipulation that is attempted in the

conscious patient, but which is more reliable if it is anaesthetized, is the cranial drawer test, a test to measure the congruity of the cranial/anterior cruciate ligament of the stifle (176, 177). Anterior and posterior movement of the tibia with respect to the femur is diagnostic of anterior cruciate ligament injury.

Pressure applied

Pressure applied

176, 177 The drawer test; with the dog lying in lateral recumbency, the hands grip the femur and tibia at the stifle. The tibia is slid cranially and caudally relative to the femur. (Arrows show direction of forces applied.)

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Radiography

The most commonly used diagnostic technique in private practice is radiography. Radiography relies upon the generation of X-rays, a form of electromagnetic radiation, and the phenomenon by which they are absorbed by the structures of the body at varying rates. The electrons that are not absorbed hit the photographic plate placed behind the desired object and turn the photographic film from white to black. The image (radiograph or ‘X-ray’) is then developed much like a photograph, or converted to a computer-generated image (178).

Radiographs provide excellent images of the bony structures of the body, but offer little assistance in the diagnosis of soft tissue injury, due to the fact that bones absorb high levels of the electromagnetic radiation and soft tissue structures do not. Therefore, all soft tissues appear grey if they appear at all on a radiograph, depending on the exposure. However, bony structures appear white and are, therefore, clearly visible. One may uncover lesions that do not seem to relate to the lameness. In such situations, these should be assessed in relation to the clinical signs of disease in order to determine their significance. Accurate positioning and the application of the correct exposure are vital if one is to obtain radiographs of diagnostic quality, although, to a degree, this has been reduced by the advent of digital radiographic imaging software.

Further imaging techniques

More technologically advanced imaging techniques are becoming more widely available to aid in the diagnosis of lameness. Although they are expensive at the moment, it is widely accepted that these techniques will become more accessible in time.

Computed tomography

Computed tomography (CT) is similar to standard radiography save for the fact that

several radiographs are made of slices of tissue in a particular region of the body in order to generate a computerized threedimensional image. The major difference to radiography, however, is that soft tissues can be differentiated and examined far better with CT scans than with conventional radiography. Nevertheless, in cases of lameness, CT scans are best employed to examine bony structures of the body in finer detail.

Magnetic resonance imaging

Magnetic resonance imaging (MRI) involves the use of a very large magnetic field and radio waves to form images, which show very good soft tissue detail. As with CT, thin slices of tissue are imaged. MRI scans are of particular relevance when injury to soft tissue is suspected, e.g. muscle, tendon, or ligament. By taking images of several closely opposed slices of a particular joint, limb, muscle, or area, the images generated can be analysed in great detail, allowing even the most minute abnormalities to be detected. Furthermore, both CT and MRI provide a significant advantage to radiography in the evaluation of structures that are superimposed.

Ultrasonography

This is only occasionally used in a canine lameness work-up; its use is restricted due to the small size of dogs, and therefore the high resolution that is required.Within the equine world, ultrasonic scanning of tendons is considered routine.

Piezo-electric crystals contained within a probe emit ultrasonic waves that can pass through most structures apart from bone, before being reflected back to the probe (179). The wavelength of these ultrasonic beams can be altered to increase the penetration of the wave, with lower frequencies travelling further than higher frequency waves. Also, the wavelength should be reduced to provide a more detailed image but without penetrating deep structures. As joints tend to be close

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178 An X-ray machine.

to the surface of the body, with little soft tissue coverage, very high-frequency probes would be required to produce images of diagnostic quality in cases of lameness. These are expensive and, therefore, rarely available to the general practitioner.

Arthroscopy

Small cameras can be placed into joints to examine their interior surfaces, through

179 Ultrasound scanner and probe (5–10 MHz) typically available in general veterinary practice.

small incisions known as ‘keyholes’. Damaged cartilage is often removed or repaired at the same time through these incisions. Arthroscopy is an extremely valuable tool when investigating lesions identified by radiography further, in order to ascertain their significance.