From the Guidelines
Fasciculations are a clear indicator of lower motor neuron disorders. According to the study published in Pediatrics in 2013 1, fasciculations are most often seen in the tongue and are associated with lower motor neuron disorders, such as spinal muscular atrophy, which can lead to rapid deterioration in acute illness. The presence of fasciculations is considered a "red flag" in the evaluation of a child with neuromotor delay, suggesting a lower motor neuron disorder.
Some key points to consider when evaluating fasciculations include:
- They are typically visible as involuntary muscle twitches
- They occur when the lower motor neurons become hyperexcitable or damaged
- They are often seen in conditions such as amyotrophic lateral sclerosis (ALS), peripheral neuropathies, or radiculopathies
- They should prompt investigation for conditions affecting the anterior horn cells, nerve roots, or peripheral nerves, as stated in the study 1.
It is essential to note that upper motor neuron disorders, which involve damage to neurons in the cerebral cortex or their descending pathways, typically produce symptoms like spasticity, hyperreflexia, and weakness, but not fasciculations. Therefore, the presence of fasciculations is a crucial diagnostic clue that can help differentiate between lower and upper motor neuron disorders.
From the Research
Fasciculations and Motor Neurons
- Fasciculations are brief spontaneous contractions that affect a small number of muscle fibers, causing a flicker of movement under the skin 2.
- The origin of fasciculations is believed to be ectopic activity generated in the motor system, with a proximal origin contributing to the generation of fasciculation in the early stages of amyotrophic lateral sclerosis (ALS) 2.
- Fasciculations are distinct from the recurrent trains of axonal firing described in neuromyotonia 2.
Association with Lower Motor Neurons
- Fasciculations are observed in patients with neurogenic disorders and in healthy individuals, and may signify the presence of a variety of disorders of the lower motor neuron 3.
- The characteristics of fasciculations in ALS and benign fasciculation syndrome have been compared, with findings suggesting that fasciculations in ALS have a shorter duration and a greater number of turns than benign fasciculations 4.
- Fasciculations are an important clinical sign in degenerative lower motor neuron diseases (LMND), and can be detected by clinical inspection, electromyography, and ultrasonography 5.
Generation of Fasciculations
- Fasciculations may be generated at any point on a hyperexcitable lower motor neuron 6.
- Physiological ('benign') fasciculations often begin suddenly and persist for years without development of muscular wasting or weakness 6.
- Fasciculations may be a sign of degeneration of lower motor neurons, and may be associated with muscle cramps and neuromyotonia 6.