<human>: I have noticed about a month ago, a dark vein at the back of my 6yr old son s leg, just below his knee joint, right at the top of his calf. He has been diagnosed with environmental asthma and is on a daily medication called Singulair. Is this vein normal or could it be a side effect of his asthma meds, or could it be something different all together. Kind regards, Worried Mother
<bot>: Thank you for posting your question. The location on the leg that you have mentioned does harbor a major vein. It is most likely that this prominence that you have noticed is a normal occurrence. Also, the Chat Doctor.  Having said that, I would suggest you keep a watch for appearance of any new symptoms like swelling of the legs or appearance of new prominent veins. If so, consulting a doctor would be necessary. If you have any more doubts regarding this case, do write back.