Part 3 of 4
Carl DeStefano DC CAC DACNB FACFN
Dena Jersild CAC DVM
Please review parts one and two of this presentation before integrating information from part 3 of this series!
The Animal Chiropractic Neurological Exam
As we perform our neurological exam we will be more sensitive and attentive to the subtleties of our patient’s response. Two important factors that are windows into the central integrative state of a neuron or pool of neurons are:
1) Time to summation and
2) Fatigability of end organ response.
Neuronal pools that are undergoing transneural degeneration will be sitting closer to threshold by the mechanisms described in part 1and 2 of these letters. There will be an increased probability that these neurons will fire with a given stimulation of a pre-synaptic pool so that their time to summation will be less. Due to the inefficiency of cellular energetic processes there will also be an increased probability that the cells will fatigue at a faster rate with a given stimulation.
Examining an end-organ’s time to summation and fatigability can give evidence of transneural degeneration (TND), somewhere in the system. By integrating information from a complete history and examination an accurate assumption on the longitudinal level of pathology or TND can be determined. From this information a therapeutic plan can be developed that is aimed at increasing the frequency of firing of the involved neurons when appropriate.
In an effort to broaden the usefulness of the neurological exam we ask you to consider the following:
- An exam procedure performed in isolation tells you nothing! Only by integrating all aspects of the history and exam can any diagnostic conclusions be reached.
- When performing a test procedure always compare one side to the other when appropriate. Is one side firing too much or is the other side firing too little?
- The purpose of each test is to ultimately find the longitudinal level of the pathologic or functional lesion.
- It is natural that the chiropractor thinks in terms of segmental (spinal) affects on end- organ response. Now consider the effects of suprasegmental or “brain-based” controls on end-organ response.
- Consider using receptor challenges as a diagnostic window (example: Does slow stretching a muscle cause a change in your neurological test?) Is the change ipsilateral or contralateral? Is the end-organ response inhibited or facilitated. Not only will the challenges help you localize the level of the lesion but they may also be helpful in choosing the most effective treatment approach.
- Consider that a test procedure may appear normal when first applied but may quickly turn abnormal with repeated application of the test secondary to TND and fatigue.
- Some tests may actually improve with repeated testing secondary to immediate early gene responses and neuroplastic up regulation.
- Most neurological testing involves a sensory input and a motor output. In animals there is difficulty in quantifying sensory loss. In the presence of some motoric response to our testing we can only say that some aspect of the sensory pathway would have to have been intact.
- With an absent or decreased motoric response to our testing we don’t know the cause so we must consider the following:
a. The receptor potential was not of sufficient amplitude to fire the second order neuron.
b. Central integration at some level of the neuro-axis was the source of not enough facilitation or too much inhibition on the cell bodies of the motor neurons.
c. There is ablation somewhere in the neurological pathway.
- With an increased motoric response to testing we don’t know the cause so we must consider the following:
a. The receptor potential was of increased amplitude because of:
– An increased environmental input (from the tester).
– An increase in receptor sensitivity (as in nociceptor sensitization or increased gamma motor neuron stimulation of muscle spindle cells).
b. The central integrative state of central neurons is in a state as to over-excite or under inhibit the cell bodies of the motor neurons.
What is a Motoric Test?
A motoric test is a doctor guided evaluation of a motor output system. These would include windows into skeletal muscle strength and tone and windows into autonomic response and tone.
Autonomic windows might include a pupillary light reflex, blood pressure, heart rate, respiratory rate and blood work for example.
Windows to skeletal muscle strength and tone would include palpation, myotactic reflexes, range of motion and postural evaluation. Those specifically trained in applied kinesiology can, with the aid of a surrogate, successfully evaluate for muscle strength.
In part 4 of this series we will look at the traditional cranial nerve and postural neurologic veterinary exam. We will superimpose our understanding of the functional nervous system described in parts 1-3 in an attempt to give greater diagnostic value to the animal chiropractic neurological exam.