What Causes Muscle Fasiculations During An MRI Scan?

Posted on Sat, 14 Feb 2015

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Sun, 15 Feb 2015 Answered on

Fri, 13 Mar 2015 Last reviewed on

Question : I have had muscle fasiculations for 6 years now and over the past year have noticed that I am weaker at times doing isometric type exercises (placing my hands on my belly while laying in bed and after a minute my arms start shaking as if too weak to hold them up and then the next morning they are sore like working out at the gym) recently I had a few mri done and noticed that the fasiculations were pretty constant during the MRI. I had forgotten about this. The other day my son had an mra at lucille packard childrens hospital at stanford and I was allowed to set in the room. Prior to the scan they used a metal detector wand to check for missed articles of metal. Nothing alarmed but everytime he waved it over my back I had this string tickling sensation. As soon as he moved to another area nothing. But as soon as it was waved over my back the same overwhelming ticklish sensation. Then during his mra I was sitting reading a book when I noticed that I was having pretty constant muscle fasiculations and it reminded me of how I had expierenced this same phenomenon during the MRI of my knees and back. Why would this occur during an MRI and why did the metal detector wand give me that strange sensation on my back?

Answered by Dr. Olsi Taka (6 hours later)

Brief Answer:
Symptoms are benign.

Detailed Answer:
I read your question carefully and I understand your concern about these phenomena.

Both MRI and metal detectors create electromagnetic fields in their vicinity and as such it is natural that at times these electromagnetic frequencies by stimulating the surface of the body cause those skin sensations and movement of body hair which align according to the electromagnetic field.

I don't believe MRI has anything to do directly with your fasciculations, but in a predisposed person such as you seem to be, it can trigger them due to the stress during the procedure. Fasciculations are known in fact to be incited by external stimulants like caffeine, amphetamines etc and in your case due to the stress related release of stress hormones, a similar circumstance is created in your body.

Judging by the duration of your fasciculations of many years most probably they are simply a case of benign fasciculations syndrome. Some routine blood tests might be useful to screen for conditions like magnesium deficiency which also predisposes to fasciculations.

If the neurologist finds some other sign during his examination he might want to recommend also an exam called EMG (electromyography) to make sure to exclude some neurological conditions.

I remain at your disposal for further questions.

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar