Assessment and testing of upper motor neuron (UMN) lesions
In the Central Nervous System (CNS), the nerves that carry the information for motor movement are called upper motor neurons (UMN). Movement that is voluntary, is located on the pyramidal track, and the cell bodies of these pyramidal tracks are located in the cerebral cortex of the brain.
From a clinical standpoint, when a patient has suffered an injury to the head, clinicians want to be able to test for any impairments in these parts of the brain or tracts (UMN lesions) by using clinical tests.
The current article highlights options for testing, and demonstrates the validity of common tests such as the Babinski test and finger and toe tapping tests to detect UMN lesions.
UMN lesions can cause positive or negative symptoms. If the symptoms are negative, they are shown as weakness in a muscle group. Positive symptoms are due to an increase in muscle activation.
Findings for positive symptoms are as follows: spasticity in a muscle group, clonus, hyper-reflexion when testing reflexes of the arms or legs, or aberrant movements on tests such as the Babinski test. The Babinski test involves stroking the sole of the foot firmly, and if the toes slowly extend rather than quickly flex/ pull away from the tester, this is a sign of a possible UMN issue. Several tests exist as part of the clinical repertoire for testing the UMNs, but the Babinksi Test is one of the most common.
This study investigated the validity and reliability of the Babinski test with three groups of participants: 1) individuals with cortical lesions that had been identified with clinical testing and imaging; 2) those with neurological illnesses that did not impact the cortex; and 3) normal, healthy individuals.
Each group comprised 125 participants. The groups were tested with the Babinski test, but also with the toe tapping and finger tapping tests. The toe and finger tapping tests were designed to test rapid and small motor movements of the participants – as fine motor movement becomes impaired in people with known UMN lesions.
It was found that the Babinski had a sensitivity of 49.6% and a specificity of 85.5%. Interestingly, the interobserver agreement on a positive toe and finger tapping test was 0.83, while the interobserver agreement on a positive Babinksi test was 0.45.
This study highlights that, while the Babinski test is a commonly used test for determining whether an UMN lesion is present, this test alone is not sensitive enough to detect a UMN lesion in all cases.
Furthermore, the relatively low interobserver agreement of the Babinski test and relatively high interobserver agreement of a finger or toe tapping test was an interesting finding as well: the observation of what a positive or negative sign is, is very critical in making a correct diagnosis.
The finger and toe tapping tests are valuable tests to add to the neurological examination to further ensure a comprehensive assessment.
Expert opinion by Jessica Povall
Not one test alone should be used when testing for cortical lesions. The more UMN tests that can be combined, along with a full motor and sensory screening, the more confident clinicians can be regarding their findings and with establishing a diagnosis.
> From: Appasamy et al., Neurol India 66 (2018) 1377-1380. All rights reserved to Neurology of India. Click here for the online summary.