T3-L3? L4-L6? What reflexes correlate with what spinal cord segments?
Spinal reflexes are an important part of the neurologic examination and must be interpreted in the context of the full examination, not as an isolated examination finding. VetGirl generally reserves checking reflexes for those patients that have abnormal gait and postural reactions. If gait and postural reactions are normal, spinal reflexes are usually normal.
To perform the spinal reflexes, the patient is placed in lateral recumbency. They should be comfortable and relaxed. If the patient is is tense with increased muscle tone, it may be difficult to obtain an accurate spinal reflex response.
A pleximeter (reflex hammer) is used to tap the tendon directly or your finger, which is lying over the tendon, used on the uppermost limb with the patient in lateral recumbency.
The spinal reflex responses are subjective, graded with the following scale:
- Absent (0)
- Depressed (+1)
- Exaggerated (+3)
- Exaggerated with clonus (+4)
The common reflexes examined include:
1) Pelvic limb spinal reflexes. These reflexes are considered the most reliable reflexes in the hind limb, specifically the withdrawal and patellar reflexes.
- The withdrawal reflex is performed by pinching a toe. A positive response is seen if the patient flexes the hip, stifle, and hock. This reflex evaluates the function of the sciatic nerve and its associated spinal cord segments (L6-S1).
- The patellar reflex is performed by tapping the patellar tendon. A positive response is stifle extension. This reflex assesses the femoral nerve and its associated spinal cord segments ( L4-L6).
2) Thoracic limb spinal reflexes. VetGirl is less thrilled with reliability of consistent and accurate spinal reflexes. Although several reflexes are present, the only reliable front reflex in the thoracic limb for VetGirl is the withdrawal reflex. Similar to the pelvic limb reflex, this reflex is performed by pinching a toe. A positive reflex response is seen by flexion of the limb. This reflex assesses the musculocutaneous, median, ulnar, radial, and axillary nerves and associated spinal cord segments (C6-T2).
Other reflexes VetGirl wants you to remember during your neurologic examination include:
3) Perineal reflex - this reflex is evaluated by touching or pinching the perineal region, with contraction of the anal sphincter seen with a positive response. Lack of an contraction of the anal sphincter may be seen with a spinal cord lesion in the S1-S3 segment or associated nerves.
4) Cutaneous trunci reflex (panniculus reflex) - this reflex is used to help localize a spinal cord lesion. This reflex is evaluated by pinching the skin just lateral to the vertebral spines bilaterally, often with your fingers in a firm manner or hemostat. A positive response is seen by a skin twitch. If the response is absent or diminished, the spinal cord lesion is 1-2 vertebrae cranial to this level would be a concern (remember: the sensory nerves travel slightly cranially before synapsing.) This reflex is commonly used in your small breed, intervertebral disc disease dogs helping to localize a spinal cord lesion.
When in doubt, make sure to practice these reflexes on normal patients, so you're aware of what abnormal looks like!