Does Nerve Dysfunction Cause Hand And Feet To Swell And Turn Black?

HI my grandaughter has experienced her hand and or feet turning black and swelling. There is a distict line between the colout change and the rest of the arm leg. She has high blood pressure. She has been in hospital over 24 hours. Although they are doing a heart scan on 4th March they now say that it is a nerve dysfunction and she will grow out of it. She is still in hospital as they are waiting for bloods to come back. Can you throw any light on this condition. Thank you