Observation versus hands-on testing

The functioning of the majority of the nervous system can be assessed by close observation (Fig. 13.2). This is particularly useful if the animal cannot be handled; for example if it is fractious or wild. For animals that you can handle, then observation is still critical for getting an overall impression of neural function and is an excellent opportunity to assess arousal and behaviour. Physical contact usually stimulates the animal and subtle deficits in mental alertness may be missed. Assessing the animal’s arousal level is done best by observing its interaction with the environment. Answering the following questions provides useful information.

Fig. 13.2 What neurological deficit can be observed in this picture of a horse? (Answer on next page.)

Does it respond normally to environmental stimuli? These may include visual, auditory, olfactory, tactile and possibly gustatory stimuli. Does it seem bright, alert and responsive or dull and somnolent? (see Figs. 11.3 and 11.4)

Is the posture of its head, body, limbs and tail normal at rest and during locomotion? (See Fig. 6.2) Does it move normally or are there signs of proprioceptive deficits (stumbling, postural abnormalities), ataxia, stiffness, pain or paresis? If so, which limbs and which joints are functioning normally and which are dysfunctional? Is there any change in muscle bulk?

Observe the head closely. Is the head posture normal? Is there any asymmetry of the face (drooping, muscle wasting)? (see Fig. 10.12) Do the ears, eyelids, eyes and nose move normally? Is it blinking? Is it sniffing at objects? Is it observing things or does it bump into them? Do both eyes track in a coordinated manner? Is there any strabismus, anisocoria or nystagmus? Does it respond to auditory stimuli? Is it swallowing normally or is there any evidence of respiratory stridor or change in voice? Is it licking its lips? Does it prehend food or drink normally?

Are there any signs of autonomic dysfunction such as anisocoria, sweating, faecal or urinary incontinence? (see Fig. 12.6) Spinal reflexes are difficult to assess by observation, but the animal may show a skin twitch if an insect lands on it, or a perineal reflex after defecating or urinating. If the animal has normal posture and gait, then the spinal reflexes are likely to be normal.

The horse in Fig. 13.2 has a left-sided facial nerve paresis. This was due to accidental compression of the facial nerve by the head collar buckle while the horse was recumbent under anaesthesia (see Fig. 10.14B). What do you observe in the horse in Fig. 13.3?

Fig. 13.3 What obvious type of deficit can be observed in this horse? (Answer in text.)

Proprioception and motor function

Normal gait requires both intact proprioception (limbs, trunk, head) and normal motor function (UMN and LMN). Similarly, for an animal to perform normally the proprioceptive tests used in the neurological examination, they require intact motor function. Therefore an animal with a purely motor problem could appear to have faulty proprioception, as it may not have the strength to place the limb in the correct position.

Assessing both proprioception and motor function is done by observing posture (trunk, limbs and head) and gait, and noting the positioning of the limbs under the centre of gravity, both at rest and during locomotion. Are the limbs base-wide or base-narrow? Are the animal’s feet placed too far to the side or do they get crossed underneath while ambulating? Note also whether the animal bears weight on the correct part of the foot or has it knuckled over and is bearing weight on the dorsal aspect.

If only the subconscious proprioception is compromised, then the limbs are often not placed under the centre of gravity either at rest or during locomotion. This results in base-wide or -narrow stance and ataxia with failure of the limbs to track under the centre of gravity when the animal is walking in a straight line. Deficits are often exaggerated when the animal turns. In horses this is seen particularly by excessive circumduction of the outside pelvic limb during tight turns.

The horse in Fig. 13.3 has proprioceptive deficits when turning in both the thoracic and the pelvic limbs. Note excessive circumduction of the left pelvic limb and the delayed movement of the left thoracic limb leaving the foot rotated inappropriately inwards.

If only conscious proprioception is compromised the animal may stand and walk with the limbs placed under the centre of gravity, but it may stand on top of the paw, or scuff the paw along the ground during the protraction phase, resulting in stumbling. Large animals, with their poorly developed corticospinal tracts, may have a remarkably normal gait with a forebrain injury; thus more complex manoeuvres are required to expose any deficit. What do you observe in the animals in Fig. 13.4?

Fig. 13.4 What neurological deficits can be observed in these animals? (Answer in text.)

Cranial nerve function

Testing cranial nerve function by observation is outlined in Tables 10.2 and 13.1. Note that as cranial nerves are bilaterally paired, both sides of the head need to be checked (see Chapter 10).

Table 13.1 Observing cranial nerve function. Note that blinking is a reflex action. The afferent stimulus is corneal drying stimulating CN V, ophthalmic branch to the brainstem and the efferent fibres travel in CN VII to the eyelids

The cat has a dilated pupil in the left eye, subtle ventrolateral strabismus and loss of tone in the upper eyelid. This cat had CN III deficit causing loss of tone in the levator palpebrae superioris muscle (elevator of the upper eyelid), medial and dorsal rectus muscles (strabismus) and the iridal constrictor smooth muscle causing mydriasis. This was due to a tumour in the floor of the cranial vault.

The dog’s neurological deficits were readily detectable by observation. Clinically, the dog’s gait was ataxic (incoordinated) and paretic. It had marked atrophy of specific shoulder muscles, especially the supraspinatus muscle. In this particular case it was due to hypertrophied ligamentous tissue in the spinal canal compressing primarily the C6 spinal cord segment. The C6 spinal nerve arising from this segment is a key component of the suprascapular nerve innervating the supraspinatus muscle. LMNs supplying the suprascapular nerve and innervating the supraspinatus muscle (see Fig. 4.7). Functionally, loss of supraspinatus muscle function compromises shoulder extension resulting in hypometria (shortened strides) in the thoracic limbs. It also compressed sensory tracts and UMN tracts passing through the region supplying both the thoracic and pelvic limbs (see Fig. 4.8). Clinically the dog’s pelvic limb gait was ataxic (incoordinated – ‘wobbly’) and paretic, while the thoracic limb gait was short and stiff. This case was an example of ‘Wobbler syndrome’ (see Fig. 6.3).

Proprioception and motor function

A key concept to comprehend is that proprioceptive testing also evaluates motor function as the animal has to move the body to perform the test. When evaluating proprioception in a limb, try not to disturb the overall position of the trunk too much as this stimulates proprioceptors throughout the body, rather than just the limb being examined, reducing the specificity of the test.

Hopping

This test is good for evaluating subconscious and conscious proprioception and may be performed, with care, in some large animal patients. In small animals, one leg is held flexed, e.g. the left thoracic limb, and the animal is pushed gently to the right. As the centre of gravity moves laterally over the right thoracic limb, this changes the subconscious proprioceptive input from the muscle spindles (stretching of muscles), joint angle receptors and Golgi tendon organs. It also changes conscious proprioceptive input by stimulating tactile receptors in the feet. In the normal animal, this will induce a lateral hop to replace the limb back under the centre of gravity. In small animals, it is useful to have the animal still bearing weight on the limb girdle that is not being tested. For example, if testing the thoracic limb, let the animal bear weight on its pelvic limbs. Thus the animal pivots in an arc around the supporting limbs; that is around the pelvic limbs when testing the thoracic limbs and vice versa. This makes testing easier for the clinician as they don’t have to try to lift the animal clear of the floor. Animals hop better laterally then medially, so only hop them laterally. Count the number of hops the animal makes on that leg, then test the other leg of the same girdle, through a similar size arc. Counting the number of hops, helps the clinician identify asymmetry between the limbs. The number of hops to cover a certain distance will depend on the size of the animal; a tall dog like a Labrador retriever takes bigger steps than a little dog like a Dachshund. An increase, or decrease, in the number of hops may indicate reduced motor or sensory function, respectively. Thus, the clinician can try to differentiate reduced proprioception from reduced motor function. An animal that has purely motor deficits resulting in reduced motor strength (e.g. myopathy) may not be able to hop properly, even though it has intact proprioception by which it can sense that its feet are not in a good weight-bearing position. Supporting the animal, by holding one hand underneath it, reduces the motor effort required to move the limb and the animal will move, or attempt to move the limb as soon as it senses abnormal limb position, but being weak, the hops will be shorter. Comparatively, if the animal has a proprioceptive deficit, it will not attempt to move the limb as soon as it is no longer in a good weight-bearing position under the body. The centre of gravity must be shifted further, creating a stronger proprioceptive stimulus to finally induce a hop. Thus the hop, if it occurs, will be bigger.

Paw position response (knuckling)

This test is more specific than hopping for evaluating tactile receptors compared with muscle receptors, thus it is good for conscious proprioceptive testing. The animal’s weight is gently pushed to the opposite side, reducing the amount being carried on the leg being tested, then the toes are flipped under (Fig. 13.5). To test for subtle dysfunction, the clinician may just turn under a single toe. The body weight is redistributed back over the limb being tested and the animal is observed to see if it corrects the foot position. To avoid stimulating joint angle and muscle receptors in the proximal leg, the clinician tries to turn the toes under without lifting the leg.

Fig. 13.5 Paw position response or ‘knuckling’ test. The foot is turned over so the animal to see if the animal will bear weight on the dorsum of the paw (the knuckles).

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