After a year of symptom onset of altered sensation and or perceived weakness in left leg and left arm with no change, how likely is it als? 20 male.

Not likely at all: The average age of onset of ALS is 55; an onset at age 20 is extremely rare (though possible). But there are other potential serious causes including multiple sclerosis and lyme disease. Please see a neurologist for an evaluation. As an aside, your root canal could lead to health problems- see http://bit.Ly/1bepu7k.

Rare: Check out the info sheet at the nih web site, http://www.Ninds.Nih.Gov/disorders/amyotrophiclateralsclerosis/detail_als.Htm. There are more common conditions that could produce the symptoms you describe. Als is very rare condition. You should definitely have a thorough evaluation to look for cause of your symptoms.