Causes and Diagnosis of Benign Fasciculation Syndrome

Benign Fasciculation Syndrome as a Diagnosis of Exclusion

Man holding leg
Jeannot Olivet/E+/Getty Images

Almost everyone has had a fasciculation — very fast twitches that may annoy but don’t move enough muscle to actually jerk a limb.  In fact, it’s not uncommon to have a fasciculation go completely unnoticed.

What is a Fasciculation?

Neurologically, a fasciculation is the spontaneous firing of a motor unit, meaning the amount of muscle innervated by one branch of a nerve. Fasciculations are common and have been described as being present in about 80 percent of normal people undergoing an electromyogram (EMG).

Fasciculations noticed by the person themselves occurs only about 50 percent of the time.

Because fasciculations can be intensely annoying and disruptive, people are often curious about the cause and whether they can be offered any relief.  

What is Benign Fasciculation Syndrome?

If people have persistent fasciculations with no clear cause, they may be diagnosed with “benign fasciculation syndrome” (BFS).  The term “benign” in this sense is not intended to downplay the disruptiveness of the fasciculations in someone’s day-to-day life, but instead to reassure that the fasciculations are unlikely to be the sign of something that will lead to more serious injury or disability.

To back this up, a study of 121 patients with a diagnosis of benign fasciculations followed those patients for up to 32 years.  None of those patients developed any serious motor neuron disease such as ALS.  In fact, about half said their symptoms had improved.

While such a good prognosis may be somewhat comforting to those with a benign fasciculation syndrome, they still have to deal with the nuisance of the fasciculations. Furthermore, some but not all patients with benign fasciculation syndrome suffer other symptoms, like general fatigue, muscle pain, paresthesias, and cramping.

Those with muscle pain or cramps may also be said to have cramp-fasciculation syndrome (CSF).

What are the "Benign” Causes of Fasciculations?

It’s important to understand that a fasciculation is less commonly related to a serious neurological illness like amyotrophic lateral sclerosis (ALS), which slowly robs people of their ability to move. More common causes of fasciculations include too little sleep, too much coffee, anxiety, stress, cigarette smoking, or strenuous exercising. There is also a  wide number of medications like Benadryl (diphenhydramine), Sudafed (pseudoephedrine), corticosteroids, or lithium that may cause fasciculations

The physiological cause of these fasciculations is unknown.  Even the source within the nervous system is a point of fasciculation.  As suggested by the wide array of symptoms, the term “benign fasciculation syndrome” should likely be pluralized, as there’s probably several different causes to those fasciculations.  

What are the Serious Causes of Fasciculations?

This all being said, a diagnosis of benign fasciculation syndrome is a diagnosis of exclusion, meaning more serious causes must be ruled out first.  In addition to motor neuron diseases, fasciculations can be a sign of peripheral nerve damage, electrolyte abnormalities, rabies, paraneoplastic syndromes, and more.

  Often, these serious illnesses can be excluded by a good neurological history and examination by a qualified professional.  Sometimes an electromyogram can be used for further evaluation.  

How are Fasciculations Treated?

Regardless of the cause of benign fasciculation syndromes, symptoms can likely be exacerbated by the same things that provoke fasciculations in anyone else.  Ensure that caffeine intake is limited, that sleep quality is good, and that there are no medications being taken that could worsen symptoms.  Sometimes stress worsens fasciculations, and this can be managed through a variety of techniques.

  Some medications such as beta-blockers, magnesium, or anti-epileptic medications have been tried with varying degrees of success.


Blexrud MD1, Windebank AJ, Daube JR. Long-term follow-up of 121 patients with benign fasciculations. Ann Neurol. 1993 Oct;34(4):622-5.

Orsin M et al. Benign fasciculations and corticosteroid use: possible association? An update. Neurol Int 2011 Jul 5;3(2): e11.

Simon NG1, Kiernan MC. Fasciculation anxiety syndrome in clinicians. J Neurol. 2013 Jul;260(7):1743-7. doi: 10.1007/s00415-013-6856-8. Epub 2013 Feb 12.

DISCLAIMER: The information in this site is for educational purposes only. It should not be used as a substitute for personal care by a licensed physician. Please see your doctor for diagnosis and treatment of any concerning symptoms or medical condition.

Continue Reading