Page 88 - Canine Lameness

60 4 The Neurologic Examination

fore requires no activation from the brain. It is critical not to confuse reflex withdrawal with con-
scious perception (such as vocalizing, head turning, etc.). Withdrawal of the limb is not a behavioral
response; it is merely a reflex and not a sign that nociception is intact. As long as the LMN system
is intact, the flexor reflex will always be present. Testing for the flexor reflex however provides the
clinician the ability to assess two components of the neurologic examination: the reflex arc and
conscious perception of pain (nociception). If the reflex is present and a conscious response is
observed, both are intact.

4.3.7.2.1 Pelvic Limb Flexor Reflex
To test the flexor reflex of the pelvic limb, the limb is extended, and using the fingers, the examiner
pinches the interdigital skin. Both medial and lateral digits, e.g. between digits 2 and 3 and digits 4
and 5, should be tested since they have different cutaneous areas (Table 4.4). The least noxious
stimulus should be used at first but can be slowly increased in intensity if there is no reaction.
Finding the area where the skin becomes thicker at the distal edge and applying the stimulus there
generally yields a more consistent response. If no response is noted, then hemostats can be used by
applying gradually increased pressure of stimulus accordingly, taking care not to damage the skin.
If still no reflex is elicited, hemostats can be repositioned to squeeze across the nail bed, the digit,
and finally the metatarsal or metacarpal bones.
The normal response for this reflex is flexion of the hip, stifle, and hock. Reduced flexion of the
tarsus indicates a lesion in the sciatic nerve, nerve roots of sciatic nerve, or spinal cord segments
(L6–S1); the hips and stifle are flexed normally since the femoral nerve remains intact. Reduced
flexion of all joints indicates a lesion in the L3–S1 spinal cord, the respective nerve roots, or the
femoral and sciatic nerves. An exaggerated reflex indicates a UMN lesion.

4.3.7.2.2 Thoracic Limb Flexor Reflex
The thoracic limb is tested in the same manner as the pelvic, taking the same care to test medial
and lateral digits. The normal response is flexion of the shoulder, elbow, and carpus. Diminished
or absent reflexes indicate a lesion in the C6–T2 spinal cord segments, the respective nerve roots,
or the named nerves. Decreased flexion of the elbow and/or carpus during testing of the with-
drawal reflex indicates deficits in the musculocutaneous and median nerves, respectively. An exag-
gerated reflex would indicate a UMN lesion, occurring either in the C1–C5 spinal cord or caudal
brainstem. However, although this is the most reliable thoracic limb reflex, some dogs with reduced
thoracic limb flexor reflexes can still have a C1–C5 spinal cord lesion and vice versa, where normal
flexor reflexes can be evident when a C6–T2 spinal cord lesion has been confirmed (Forterre et al.
2008).

4.3.7.3 Perineal Reflex
The perineal reflex tests the integrity of the S1–S3 spinal cord segments as well as the caudal nerves.
The skin of the perineum is stimulated using forceps or a cotton‐tip applicator. Both right and left
sides should be tested. This reflex may be diminished in patients that have lesions affecting the
sacral spinal cord or cauda equina, especially if urinary bladder dysfunction is present, for example
degenerative lumbosacral stenosis. The normal response is ipsilateral contraction of the perineum.

4.3.7.4 Cutaneous Trunci (“Panniculus”) Reflex
The cutaneous trunci (previously called panniculus) reflex tests the sensory integrity of all dermato-
mes over the thoracolumbar vertebral column, which are supplied by the dorsal branches of each