A doctor happens to feel that when sclerotherapy is used, for instance, on the upper leg that new surrounding spiders will form. how true?

In part: Some are gone forever, but some do collateralize as time passes.

Not true.: Sclerotherapy is the gold standard of treatment for spider veins. With the newer sclerotherapy agents, smaller needles and better equipment such as syris and veinlite, we are able to have excellent results. Two things to note: sclerotherapy is a process and will take several treatments and requires maintenance, and if there are extensive spiders, then a venous reflux sonogram may be necessary.

The question: Was new spider veins formation after sclerotherapy but the answer you got was unrelated... Indeed it can happen randomly that sclerotherapy for any type of vein can induce the formation of new, fine , red colored so called second generation of spiders or matting usually quite resilient to treat. If varicose veins are injected a good compression may prevent their occurrence.