Red/purple spots on thigh, clustered closely together, covering large area, long streaks. had very similar rash before several times over the years. ?

Exam needed: Such an eruption could be due to inflammation of tiny blood vessels(vasculitis) which may be caused by an autoimmune disorder or leakage of blood from capillaries(petechiae) seen with low platelets,for example. Your physician or dermatologist would have to inspect this eruption in order to make a diagnosis and order any appropriate tests.