Page 86 - Canine Lameness

58 4 The Neurologic Examination

extensor carpi radialis, biceps, triceps, patellar, cranial tibial, and gastrocnemius reflexes. The
flexor (i.e. withdrawal or pedal) reflex of the thoracic and pelvic limb has a multisynaptic (i.e. mul-
tiple neuronal pathways) reflex arc and is the more consistent reflex.
Spinal reflexes are graded on a scale of from 0 to +4: Absence (0) or diminished (1+) reflexes indi-
cate a complete or incomplete lesion, respectively, in the sensory or motor component of the reflex
arc. This would indicate an LMN lesion, although differentiation between lesions of the nerve (neu-
ropathy), neuromuscular junction (junctionopathy), and muscle (myopathy) are not always feasible
based on the reflex assessment. In general, loss of reflexes in one muscle group indicates a neuropa-
thy (e.g. the femoral nerve). Bilateral reflex deficits are more common with a segmental spinal cord
lesion that affects the motor neuron in the gray matter, such as a midline compressive L4–L5 lesion
causing reduced bilateral patellar reflexes. If multiple myotatic reflexes are diminished or absent,
then a spinal cord lesion, polyneuropathy, myopathy, or abnormalities in the neuromuscular junc-
tion may be suspected. Normal (2+), exaggerated (3+), and clonic (4+) reflexes occur when there is
loss of the inhibitory UMN pathways resulting in myotatic reflexes being increased. Increased mus-
cle tone usually accompanies these exaggerated reflexes. Clonus is more often seen in chronic
lesions. Exaggerated reflexes should not be overinterpreted. If gait and postural reactions are nor-
mal, then reflexes are usually normal. If the reflexes appear exaggerated in this case, this is most
likely examiner error or increased muscle tension (e.g. due to patient anxiety).

4.3.7.1 Myotatic (Stretch) Reflexes
A plexor (pleximeter) is used to perform the myotatic reflexes. Generally, the flat surface is used
when striking tendons while the pointed edge is used on muscle bellies. In small or chondrodys-
trophic dogs, the handle can provide a focal contact on tendons. Reflexes will be easiest to interpret
in the relaxed dog lying in lateral recumbency.

4.3.7.1.1 Pelvic Limb Myotatic Reflexes
The patellar (quadriceps) reflex tests are the most reliable myotatic reflex of the pelvic limb. However,
neurologically normal dogs, 10 years of age or older may have reduced or absent patellar reflexes in
one or both limbs (Levine et al. 2002). In these dogs, gait and postural reactions should be normal.
The reflex is performed with the patient lying in lateral recumbency. A supportive hand is placed
under the femur, allowing the stifle to flex slightly. Excessive flexion or extension of the stifle joint
can falsely influence the appearance of the reflex. The patellar ligament is struck crisply using the
flat surface of the plexor and the stifle briskly extends. The normal response is for the stifle to extend.
The cranial tibial and gastrocnemius reflexes are less reliable and therefore less frequently per-
formed. Interpretation of the results should be performed with caution (Lorenz et al. 2011; Dewey
and Da Costa 2016). The cranial tibial reflex is performed with the patient in lateral recumbency,
and the limb is held parallel to the ground while the belly of the cranial tibial muscle is struck with
the plexor, midway along its length. To elicit the gastrocnemius reflex, the metatarsal area is grasped
so that the tibiotarsal joint is held in flexion while the common calcanean tendon is struck with the
pleximeter above the calcaneus.

4.3.7.1.2 Thoracic Limb Myotatic Reflexes
There are no reliable myotatic reflexes for the thoracic limb. The biceps and triceps reflexes are
difficult to elicit and while the extensor carpi radialis reflex can be easily elicited, there is debate of
its value since it can be elicited in limbs with a transected radial nerve. If these reflexes are per-
formed, they should be interpreted with caution and in context with other findings and compared
to the unaffected (if available) limb.