APPROACH TO NEUROLOGICAL PROBLEMS OF THE PELVIC LIMBS
A wide variety of neurological conditions can cause problems affecting the pelvic limbs, either through
weakness, sensory impairment or pain. More confusingly, many musculoskeletal problems can present in a
similar manner, resulting in a long list of potential diagnoses.
The primary job for the clinician is to address the first two questions that direct the approach to any
neurological case, namely whether there is a neurological problem and, secondly, what is the site of that
lesion? Only then is it possible to shorten this list of possible diagnoses and direct appropriate further tests.
This requires an understanding of the neurological examination.
Neurological examination
The aim is to explain all the neurological deficits by:
1.
A single lesion site – if possible
2.
A single lesion system (e.g. all the peripheral nerves) – if a single lesion doesn’t make sense
3.
A multifocal condition – if single lesion and single system don’t make sense
Tests performed
1.
Reflex tests
2.
Postural tests
3.
Tests of sensation
DRG
REFLEX TESTS
Abnormality = abnormality somewhere
in the reflex arc
Sensory axon
GM
Muscle
WM
Motor axon
NMJ
© P M Smith
Spinal Reflexes
Thoracic limbs
Pelvic limb
Biceps
Patellar
Triceps
Myotatic Reflexes
Gastrocnemius
Extensor carpi radialis
Tibialis cranialis
Withdrawal
Withdrawal
All of these reflexes are not necessarily present – obtaining a gastrocnemius or tibialis cranialis reflex in the
pelvic limbs can be difficult in normal dogs, so you shouldn’t necessarily ascribe too much significance to
whether these are present or not. A patellar reflex is a much more consistent findings and its absence much
more likely to be significant.
As with other aspects of the clinical examination, the findings should be viewed in the context of the clinical
presentation – for example, you wouldn’t necessarily get excited about a dog having a mild heart murmur if
it was presented with a skin condition; in a dog with coughing and exercise intolerance, this could be a
different matter. You should also pay particular attention to whether the responses are symmetrical
Postural Tests
Abnormality = abnormality somewhere
between foot & brain
© P M Smith
Postural tests
Proprioceptive positioning – flex foot to ‘knuckle’ the foot over
Paper slide test – put a piece of paper under the foot and move it laterally to test re-positioning
Placing – pick the animal up and approach the table – foot should extend to the table. N.B. Vision may
compensate for poor proprioception
Hopping – hold the animal and move the torso until the animal hops to support itself
Hemiwalking – lift front and back legs up on one side and make the animal walk sideways
The CNS is divided into clinical compartments on the basis of reflexes:
Brain
Cranial nerves
C1-C5
T3-L3
© P M Smith
C6-T2
L4-S3
This division is fundamental to understanding how to localise a lesion in the nervous
system
Interpreting the neurological examination
Abnormal reflex = abnormality somewhere in the reflex arc. For spinal cord disease, diminished reflexes in
the pelvic limb suggest a lesion in the region L4-S3 and in the thoracic limb, C6-T2.
Abnormal postural response = abnormality between foot and brain. For CNS disease, a lesion anywhere
from the brain to the sacral spinal cord segments will impair pelvic limb responses and a lesion between the
brain and T2 can impair thoracic limb reflexes.
By putting the results of reflex and postural testing together, it is possible to place a lesion
in one of the clinical compartments of the CNS shown above.
ADDITIONAL TESTS
Perineal reflex – afferent and efferent in the sacral spinal cord segments. Touch/pinch the perineum and
anal sphincter contracts; tail usually pulled down as well. This is useful for dogs presenting with hind limb
pain/limping, since it helps to determine whether or not a lesion is likely within the spinal canal – evidence
of sacral nerve involvement makes is more likely that this is the case.
Cutaneous trunci – often called the panniculus. The motor arm arises from segments C8-T1 but the sensory
input is segmental, entering the spinal cord through each pair of spinal nerves in the thoracolumbar spinal
cord before running cranially. A spinal cord lesion between T3 and L3 may interfere with this ascending
sensory information and produce a poor response to pinching the skin of the dorsum (normally a twitch of
the skin) caudal to the lesion. For dogs which are limping/have paresis from a neurological lesion between
T3 & L3, the spinal cord lesion may well not be severe enough to impair this reflex, so don’t rely on it.
Segmental sensory
© P M Smith
Motor
Note that the sensory fields sweep caudally, so that the position at which the reflex becomes poor is likely
to be caudal to the site of the spinal cord lesion
Muscle tone – both in the limbs
Observation – simple and useful; it helps to detect subtle asymmetry and also allows an assessment of
behaviour, which is affected by forebrain function
Direct palpation – may help with some conditions, particularly painful diseases affecting the spinal
cord/nerve roots. This is important in dogs with neurological conditions affecting the pelvic limbs,
particularly if there are no neurological deficits.
PITFALLS
1.
Spinal shock. If you cut the spinal cord between T3 and L3, the immediate result is a loss of muscle
tone in the pelvic limbs and loss of spinal reflexes – this is CONTRARY to the conventional way that
neurological examination is viewed. This phenomenon is very important in humans, since it persists a
long time, and makes localisation very tricky; it lasts for much less time in animals but may be seen
soon after very severe spinal cord injuries i.e. you may see this in practice. In these cases, it’s a good
idea to re-examine cases sequentially to be certain about what’s going on (not a bad idea in general,
in fact).
2.
Schiff-Sherrington response. Conventionally, a T3-L3 lesion will increase tone in the pelvic limbs but
not affect the thoracic limbs; however, severe lesions in this region can cause an increase in tone in
the thoracic limbs because of inhibitory fibres here that project cranially to C6-T2 region.
Both phenomena occur in severe, acute spinal cord injury. In such cases, there should be no confusion
with orthopaedic diseases. However, the withdrawal reflex can be impaired in the affected leg in dogs that
present soon after lateralised spinal cord injuries (e.g. peracute disc extrusion, FCE), likely representing
spinal shock.
PROGNOSIS
This isn’t really relevant in a discussion about hind
limb lameness but is an important component of
the neurological examination and is therefore
worth touching on here. The presence or absence
of pain sensation can give useful information
about prognosis in dogs with spinal cord injury i.e.
absent pain sensation gives a much worse
prognosis. Remember that the withdrawal reflex is
a segmental spinal cord reflex, so even a dog with
a transected spinal cord should retain this.
You can use: Fingers
Artery forceps
Atraumatic pliers
© P M Smith
DO NOT MISTAKE A WITHDRAWAL REFLEX FOR EVIDENCE OF INTACT SENSATION
DIFFERENTIAL DIAGNOSIS
Almost any neurological condition affecting the spinal cord and/or nerves can be considered in dogs
presenting with neurological lameness. You can find a list of possibilities in any text book, so repeating this
here is pointless.
The neurological examination will go a long way to shortening the list of possibilities. Intervertebral disc
lesions are a relatively common cause of neurological lameness but any lesion that compresses a nerve or
nerve root can cause pain (neoplasia; osteophytes). Infections are relatively rare, though discospondylitis is
painful and a relatively common site for infection is the lumbosacral junction, so dogs can present with
pelvic limb lameness; infectious diseases of the nervous system are rare in this country. Vascular lesions of
the spinal cord can resemble a lameness – as can any condition affecting the spinal cord. In addition, lesions
affecting the muscles, nerves and neuromuscular junction can also appear lame, though more typically
would be bilateral.
As mentioned above, the most difficult component of the whole process is often in distinguishing
neurological from musculoskeletal disease, so you have to consider a range of orthopaedic conditions until
the examination has excluded these. As well as the examination, the onset, progression and presence or
absence of pain are key components of a case that will help to focus further tests.