I can see that your are concerned about your condition but more often than not, the presence of these veins is normal. Although to rule out something else, you should consult your doctor and ask him to get a doppler ultrasound
of your arm. This investigation is an ultrasound of the veins and arteries of your left arm and hand and this will put your apprehensions to rest.
Do you suffer from diabetes?
Hope you get well soon.