Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.
Q: Context: Puffy hand syndrome is an unrecognized complication of intravenous drug abuse. This painless syndrome appears during or after a long period of drug addiction. It involves the hands and sometimes the forearms, and may cause functional, aesthetic and social disturbances when the hand volume is important. Physiopathological mechanisms of the puffy hand syndrome are unclear and include venous and lymphatic insufficiencies, infectious complications and direct toxicity of injected drugs and their adulterants. Low-stretch bandage and elastic garment, usually used in lymphedema treatment, are proposed to treat the puffy hand syndrome.
Question: What causes "Puffy hand syndrome"?
A:
intravenous drug abuse