From the Guidelines
Fasciculations are a hallmark of lower motor neuron lesions, not upper motor neuron lesions. These involuntary muscle twitches occur when there is damage or dysfunction affecting the lower motor neurons, which are located in the anterior horn of the spinal cord or in the motor nuclei of cranial nerves in the brainstem. According to a study published in the Journal of the American College of Radiology in 2020 1, patients with suspected motor neuron disease, such as amyotrophic lateral sclerosis (ALS), typically present with both upper motor neuron degeneration (characterized by hypertonicity and hyperreflexia) and lower motor neuron degeneration (characterized by muscle fasciculations, weakness, and atrophy). Key characteristics of lower motor neuron lesions include:
- Muscle fasciculations
- Weakness
- Atrophy In contrast, upper motor neuron lesions typically produce symptoms like:
- Spasticity
- Hyperreflexia
- Babinski sign It's essential to evaluate fasciculations clinically in the context of other accompanying signs to determine their clinical significance, as they can be seen in various conditions, including ALS, peripheral neuropathies, radiculopathies, and certain metabolic disorders, as well as in healthy individuals as benign fasciculations 1.
From the Research
Fasciculations and Motor Neuron Lesions
- Fasciculations are visible, fine, and fast contractions of muscle fibers that occur spontaneously and intermittently 2
- They are often associated with lower motor neuron disorders, and may signify the presence of a variety of disorders of the lower motor neuron 3
- Fasciculations can be generated at any point on a hyperexcitable lower motor neuron, and may be a sign of degeneration of lower motor neurons 4
Diagnosis and Clinical Significance
- Fasciculations can be detected by clinical inspection, electromyography, and ultrasonography, with ultrasonography being the most sensitive method 5
- The presence of fasciculations alone is not enough to implicate early diagnosis of motor neuron disease, and disease progression is probably the single most important historical characteristic for diagnosis 6
- Signs of active denervation, such as fibrillation potentials, are critical for diagnosis, and chronic weakness should be proportional to either atrophy or upper motor neuron signs in the affected muscle 6