Much different than a regular muscle spasm, fasciculations can be a sign of a major neurological disease such as ALS, otherwise known as Lou Gehrig's disease, or they can also result from other nerve disorders, or spinal damage, Lyme disease, and many other causes...Also they can be benign...If you have twitching like this accompanied by a feeling of weakness or fatigue, make sure to visit the doctor for further testing and request an EMG.. Don't wait for atrophy to set in before being tested. I had denervation in both legs, one arm and both lumbar paraspinals, and my left thoracic paraspinal...This pointed to a strong possibility of ALS, yet my weakness ceased in its progression. Although I still have lot's of weakness, my muscles have not wasted away...The theory is that I had a virus which mimicked the start of limb onset ALS, and it was finally the lack of progression that ultimately determined my diagnosis.