PAUL MONIZ: Dr. Marks, what exactly are kidney stones?
JON MARKS, MD: Kidney stones are combinations of protein, calcium, and various other minerals that precipitate out of the urine, that settle out of the urine, so to speak, within the kidney and can lodge either in the kidney or elsewhere along the urinary tract.
PAUL MONIZ: Is it true that these crystals are normally present, but the systems of the body tend to cancel each other out and allow urine to come out in a stream?
JON MARKS, MD: There are, indeed, present in the urine of most people substances which prevent the crystals from aggregating and forming together to form a stone. And in that situation, when the patients do not have sufficient prohibitors or preventers of stones, they will form the stones.
PAUL MONIZ: Dr. Marks, can you show us in the diagram that you have there exactly where the stones form?
JON MARKS, MD: This is an illustration of a number of different pathologies within the kidney, but this is the kidney here and this is the ureter which leads down from the kidney down towards the bladder. If we travel back up just a little way, we'll see a very small stone here which is lodged in the ureter which accounts for the typical feeling of kidney stone pain or renal cholic. But if we travel further up, we find that within this area here, an illustration of what's known as a staghorn stone.
PAUL MONIZ: In the patient that had a stone that size in that position, would the patient feel pain?
JON MARKS, MD: Frequently patients with stones that size don't feel pain. They have urinary infection. They may have blood in the urine detected microscopically. Those are somewhat less symptomatic stones. Unfortunately, those are the stones that can have the most devastating effect on the kidney because they are in some sense silent.
PAUL MONIZ: Dr. Salant, let's bring you into this, more on the pain in just a moment. When do stones usually strike?
ROBERT SALANT, MD: The most common onset of stones is in a male patient, and it's probably a 2:1 or 3:1 ratio of male to female. The typical age of onset is somewhere between 30 and 50 years. However, stones can occur in children as young as 8 and 9 with metabolic abnormalities, and can also occur in the elderly for the first time.
PAUL MONIZ: Let's talk, Dr. Marks, about the pain. Why are the stones so painful?
JON MARKS, MD: A stone sitting innocently in the kidney frequently is not painful. But as the stones move about the kidney and in particular when they descend down the ureter, as I illustrated earlier, they create inflammation, they create local swelling. That causes, in a sense, a backup of urine behind the stone. It's that backup of urine that by and large is responsible for the pain the patients feel.
PAUL MONIZ: Very good information. Dr. Robert Salant, thank you for your time. Dr. Jon Marks, for your time as well. I'm Paul Moniz. Thank you for joining us. Remember that kidney stones are common, affecting about 10 percent of the American population at one point or another. Thanks for being with us.