Frequent muscle twitching and paresthesia, what are the underlying causes of these symptoms?

Depends where, How often, and what brings it on. Twitching and parasthesias can be caused by numerous things and it would be difficult to speculate with just a little history such as this. It could be anything from dehydration to ms, but we would have to know much more prior to even suggesting a diagnosis. See a physician for a thorough history and physical exam.