Page 90 - Canine Lameness

62 4 The Neurologic Examination

In animals, however, one nociceptive pathway predominates (spinothalamic tract) making the dis-
tinction between deep and superficial pain very difficult. In this text, the term nociception will be
used to infer the patient’s perception of a noxious stimulus.
In patients with severe transverse spinal cord lesions (i.e. paraplegic or tetraplegic), nociception
should only be assessed in limbs that have absent voluntary motor and where the presence of
sensation has not already been established. Any noxious stimulus that elicits a behavioral response
may be used to confirm the presence of pain sensation. Pinching the digit or interdigital webbing
may be adequate in some animals. When a response is more difficult to elicit, hemostats should be
used. If there is no response to a noxious stimulus applied to the toes, then the same stimulus can
be applied to the metacarpal/‐tarsal bones. If there is no motor present in the tail, nociception can
be assessed in a similar caudal to cranial direction.

4.3.8.2 Spinal and Limb Palpation
Palpation of the limbs and vertebral column is performed from distal to proximal and caudal to
cranial, respectively. Palpation should always begin using a light touch to prevent more forceful
than necessary maneuvers near a painful or unstable region, which could be dangerous to the
patient (e.g. unstable vertebral fracture) or the examiner (e.g. aggression provoked from pain or
fear). Details of lumbosacral and cervical palpation are described in the respective Chapters 16
and 21.
It is important to consider that pain assessment is subjective, as well as examiner and patient
dependent. Also, pain can be referred from other sources (e.g. abdominal pathology or intracranial
disease causing spinal hyperesthesia) or transfer to appendicular skeletal structures. For example,
a patient may react or sit when pressure is applied, downward onto the caudal lumbar spine, if
some of this pressure is conveyed onto painful stifle or coxofemoral joints.

4.3.8.3 Cutaneous Sensory Testing
Nervous system lesions typically cause loss of sensation caudal or distal to the lesion, and in many
cases, sensation will be increased at the site of injury. Therefore, the distribution of cutaneous
sensory loss provides great localizing information as lesions can be pinpointed to a specific nerve
or two to three spinal cord segments. For this purpose, areas of increased sensitivity (hyperesthe-
sia), decreased sensation (hypoesthesia, also called hypesthesia), or absent sensation (anesthesia)
are evaluated and mapped out. This concept is also used during the flexor withdrawal and cutane-
ous trunci reflex testing as described above. Similarly, testing can be performed along the other
zones described, such as autonomous zones of the limbs (Figures 4.5). Testing is generally per-
formed using a hemostat (as described above) and is started caudally or distally and advanced
cranially or proximally, respectively. The direction can be reversed to better map the specific point
where decreased sensation transitions to normal sensation. If the patient displays a behavioral
response at any point during the exam, then sensation is present, and giving a more severe stimu-
lus is not necessary.
The autonomous zones most commonly tested in the thoracic limb include the skin of the dorsal
paw for the radial nerve, the medial surface of the antebrachium for the musculocutaneous nerve,
and the caudal surface of the antebrachium for the ulnar nerve (Table 4.4, Figure 4.5). Due to over-
lap from the ulnar nerve, the median nerve does not have an autonomous zone. In the pelvic limb,
sites for testing autonomous zones include the craniolateral surface of the thigh for the lateral
cutaneous femoral nerve, the caudal aspect of the proximal thigh for the caudal cutaneous femoral
nerve, the proximal medial surface of the thigh and prepuce or vulva for the genitofemoral nerve,