Hi pizzaman - These strange sensations can be related to misfired nerves (called paradthias). I had a long period of time where I thought I had shampoo or soap running down my shoulder blade after I got out of the shower. I'd repeatedly have my husband look to see what was there - nothing! This was 4-5 years before my Dx.
Having said that, nerves can misfire for many reasons, and I have no idea if that was related to my Dx. I think it's worth mentioning to your doctor, but I wouldn't be too concerned with that one symptom. Also, while MS does run in some families, that seems to be the exception. There has been no scientific that it is passed down. I know it's hard not to worry anyways.
Make that appointment for peace of mind. You will feel better hearing from a doctor.