As you mentioned, you are suffering from an itchy variant of pigmented purpuric dermatosis
. It is sometimes associated with excercise and legs in dependent position for prolonged period( as in air travel for long hours). So avoid keeping leg in dependent position, keep moving your legs while travelling for long hours so that no blood stasis
occurs in leg vessels, you can also wear elastic compression stockings. Take an anti allergic medicine for itching and continue with your doctor's prescription. Take care.