In these pages we are taking a deep dive into the scoring the Neurocom CDP.
When one is doing the Neurocom CDP test, there are two modules - -the "Sensory" tests, and the "Motor" tests. While other pages have discussed the sensory tests in detail, this section is on the motor tests.
The motor tests are further subdivided into one involving translations (i.e sudden forwards-backwards jumps of the support surface) -- called the motor control tests, and rotations of the support surface, called the "adaptation tests". While there is vestibular stimulation, the main input here is somatosensory from the feet -- sheer in the first case, and ankle rotation in the second. So one would think that these tests would not be vestibular evaluations, but rather more closely related to sensation in the feet. We think that this test is both underused and underreported. It is not a vestibular test, but it does provide information about sensation from the feet as well as musculoskeletal function.
The above is a normal MCT test.
The motor control test evaluates automatic motor reflex responses to sudden, unexpected forward and backward translations of the support surface (NeuroCom International, 2000). The amplitude of the translations is determined by the individual patient’s height. Three consecutive trials of small, medium, and large translations are recorded for both backward and forward perturbations. A score is determined for latency, weight symmetry, and amplitude scaling. Reports in the literature mainly report latency.
Latency refers to the time it takes for the automatic postural response to occur following the onset of platform translation. Latencies are calculated for each leg and each translation and are valuable for identifying motor system abnormalities (Nashner, 1997). Prolonged latencies imply dysfunction in any one or a combination of the components which comprise the long-loop automatic motor system and are most often associated with central and/or peripheral nervous system lesions (Nashner, 1997; Nashner, 2008).
Weight symmetry refers to the percentage of body weight that is placed on each individual leg during the motor control test (Nashner, 2008). Amplitude scaling provides indication of the strength of the postural response (Nashner, 2008).
As noted below, the MCT test is also affected by mechanical issues such as Achilles tendon injury. It would seem likely that it is affected by bony fusion of the ankle as well.
We suspect the MCT test is affected by anxiety and body weight as well, with the amplitude of responses increasing with both (Olchowik et al, 2014). We would expect the latencies to be unaffected.
|This man has an advanced diabetic neuropathy, and his latencys are longer than normal. (Graphic courtesy of Dr. Marcello Cherchi).|
As described by Nashner (2008), "The adaptation test assesses the ability to balance on irregular surfaces by suppressing automatic reactions to surface perturbations when they are disruptive to our stability" (p. 172). During the adaptation test, the patient attempts to maintain his or her balance during identical sequences of fve toes-up and fve toes-down rotations of the platform (Nashner, 2008). The amplitude of the patient's sway is measured immediately following each surface rotation
Measurements indicate how well the patient is able to utilize adaptive mechanisms to enhance stability (Nashner, 1997).
Fransson et al (2000) have written extensively about postural adaptation, but mainly use methods involving vibration applied to the calves or neck to manipulate proprioception.
Stal et al (2003) reported that numbing of the feet (using hypothermia). They reported "The reduction of cutaneous sensor information from the mechanoreceptors of the feet significantly increased the vibration-induced torque variance mainly in the anteroposterior direction. However, the effects of disturbed mechanoreceptors information was rapidly compensated for through postural adaptation and torque variance was in level with that without anesthesia within 50 to 100 seconds of stimulation, both when standing with eyes open and eyes closed." It is difficult to compare the "apples vs oranges" situation here where we have different perturbations and different outcome measures. Still, it does suggest that there is very rapid adaptation to loss of feet sensation in normal individuals, and thus one might expect that abnormal responses might require either a larger loss of sensation, or the combination of several deficits in sensory or motor control at the same time.
We were unable to find any research papers reporting this test in patients with neurological issues. One would expect that patients with severe cerebellar disorders would not show adaptation.
References (for all CDP pages)