Obstruction produces the main burden of kidney stones. It causes stone pain. Obstructing stones reduce kidney function and evoke inflammation that both are transient because stones tend to pass or are removed. Obstruction favors infection as urine stagnates above it, and an infected obstructed urinary tract not rarely causes sepsis. Infected or not, if allowed to obstruct for too long a time, stones can injure kidneys enough they lose function permanently.
In his review of stone pain, MIke Borofsky showed us how kidney function falls and inflammation arises in obstructed kidneys of animals. I focus here mostly on data from patients.
What is Obstruction?
It is a plug or it is a dam.
Sometimes a stone occludes the ureter completely so nothing passes by it. Sometimes it occludes the ureter partially forcing urine through a narrowed channel. That narrowed channel raises resistance so flow requires higher pressure. Above a stone, plug or dam, pressures go up, in the ureter and in the tubules of the kidney. Stretch causes pain, pressure reduces the function of the kidneys.
Perhaps because most stones obstruct the kidneys only briefly, for some hours or days, they damage kidneys slightly or not at all. But physicians know to be vigilant and act if a stone obstructs for too long. This tells patients a simple story: Never omit a followup visit physicians request when a stone is passing. After a day or so pressures fall above a stone, pain may cease, yet obstruction remains.
Unfortunately, stones may produce no pain and yet, undetected, damage a kidney or destroy it. excellent reviews. So stone formers benefit from wariness and, faced with new bleeding, problems voiding, fall in urine volume – any urological symptom – do best letting their physicians know. Better a pest than a victim of kidney loss from silent obstruction. Notably, experts find that after stone removal by ureteroscopy risk of residual obstruction warrants the cost and radiation exposure of another radiograph.
Despite these exceptions, most stones are not silent and their pain has special traits of immense diagnostic significance.
Who but the denizen of that body can know a bodily pain? Yet so many patients have told me their stories I feel a confident reporter of what they have said. No references here; textbook writers, writers of reviews have heard no more than I have heard. They own no better words than I to tell about this odd symptom. My patients have taught me well, and I shall tell to you what they have told to me.
Not always, but as a rule the pain of a documented stone attack begins suddenly though often with modest severity. By a ‘documented’ attack I mean pain accompanied by stone passage or removal. I also mean the patient has a clear memory of the episode. Often, I ask where the person was when it started, in what room, where in it. Most know, for howsoever modest at the beginning stone pain is so distinct, so peculiar, it impresses itself upon memory even when mild.
No change of position, no motion lessens the pain from a documented stone. It possesses an indifference to all actions. I use this indifference to practice by. What makes pain better, I ask, or worse? When from a documented stone all tell me bending nor moving or anything else they might do affected the pain. Those who have experienced documented stone passage speak of indifference as a way to tell the difference between a stone attack and all other back pains. Not the only difference, but surely one of them.
Over time, I say between 30 minutes and a few hours, the pain mounts to a plateau of severity and although people speak of waves of pain what I hear is a more constant pain about which nothing can be done. Eventually, the pain subsides, or patients require emergency treatment. Often of legendary, miraculous proportions, stone pain demands treatment. Narcotics, NSAIDs – at home by experienced, stalwart patients, and in emergency rooms for the rest. But not always; stone pain can be modest if disturbing. Patients who read this will rail at me. Some that I make too much of the pain and scare people. Some that I slight it and deny their suffering.
How can I who am at second hand, a mere reporter at best but offer my apologies to all and persevere. For it I demur to write about the pain, criticism will mount to heaven – who would forgive such an omission?
Poets and writers who have put in words for me this pain seem lost in thought as if words to describe it might not exist. But I have gathered the pain is as a burning bore twisted into the body, strange and never before felt, vague as to location within the flank, unmistakable once experienced, sometimes horrifying sometimes less serious. One hears some women say childbirth pales before it. And, they sey, as an added vexation, it brought no reward.
Just as you might think, they point to the back, just below the ribs on one side or the other. Famously, as a stone moves down the ureter so moves the pain. If I hook my thumb behind my waist and spread my fingers out in front I cover the general space it moves through – downward, increasingly anterior, ultimately into the pelvis or near it. At the junction of the bladder and ureter a stone sets up the symptoms we usually think of as urinary infection – frequency, urgency, burning pain on urination. So many times have patients been told about infection when it was a stone there. As much as suddenness, is downward motion a mark of stone.
Vomiting, diarrhea, flushing, high blood pressure – if one measures it, all can accompany stone pain. Vomiting dehydrates some patients enough they require intravenous fluids, thence emergency room visits. I could recite colorful stories about the futile actions and contortions that patients attempt. But can one not call such recitations ghoulish, or faintly pornographic, even? When stone pain is torture, my eyes turn away in horror at it, and my pen drops. Let me say, merely, my life efforts at prevention arose, partly, as a response to it and to all it engenders, of drugs, of surgeries, of lost work, lost relationships, disrupted families, and worse.
Stone pain ends, when it ends, as if by magic. Let the stone move so obstruction lessens, and pain can disappear. Surgery and pain medications blur the ending and obscure its magical character so only some patients can report the ending with complete clarity. But those who can not rarely tell about it with a tilt of the head upward and to one side, and eyes that turn in that direction, as if looking, as they remember the experience, for some possibly divine agency of their deliverance.
The Whole of It
I read to you from a palimpsest, from the overlaid voices of a thousand patients who shared their recollections with me. More than a thousand – thousands, over decades. Long ago I thought to record them, extract, it may be, some statistical pattern. Eventually I came to despise the idea. They, those many people who witnessed their special horrors, shared with me a knowledge the most of us can never know. Should one not honor such confidences with memory and words enough?
In the great round and oddly resonant amphitheaters of those antique times before writing, bardic poets, I have read somewhere, performed whole epics from memory. I understand their knowledge passed down the generations unwritten from old to young. Was medicine not already there? Did we not gown ourselves and, set apart, listen and, with whatever we could use, stand against the rebellions and terrors of the body, against accident, and chance, and fate?
Nowhere in my life, nowhere in my craft or art have I felt more a physician than when I hear the stories, the peculiar and oddly reliable character of the one symptom that more than any other is the very make and mark of stones.
So here is what I never did with my computer, here are the main facts of renal colic: a pain sudden, indifferent and often terrible that ends, sometimes, even on the instant, like magic.
Other Clues to Obstruction by Stones
Take away colic how could one imagine obstruction by a stone? What would lead one to the idea so imaging is done?
Stones cause bleeding, and bleeding usually leads to imaging.
Obstruction promotes infection. Stasis is the usual explanation. Dam or plug, a stone reduces the ratio of flow to the volume trapped above it so bacteria, common in urine, sweep downstream more slowly as when a fast running river widens into a lake. Upstream longer and prone to divide, they can increase their numbers and invade the kidneys. Fever, chills, malaise – all are common but pain from inflammation may point to a kidney whose obstructing stone itself was silent.
Suspicion has virtues for anyone with stones. A simple ultrasound examination, a simple radiograph may show a stone that somehow failed to sound its common claxon, the unique and warning colic.
Other Causes of Flank Pain
Radiologists have perhaps the best view. Patients come with symptoms that point to kidneys, they perform CT exams and see the causes.
Kidney Damage from Obstruction
All the while a stone obstructs, the kidney above it suffers and if it goes on too long, that suffering, the kidney dies. It shrinks up into a scarred remnant that will never again contribute to the economy of the body, never again guard against the salts and fluids, never again cleanse the blood of the debris of life that must be rinsed away minute by minute for a perfect health to endure.
It is from animals we have learned the minute details of what obstruction does to kidneys. But we have some information about patients from the study of patients and, being from humans with this disease such information has about it aspects of immortality.
Loss of Kidney Mass
Wonderfully antique and from an age before cell phones and CT scanners, here is an 18 year old woman in whom a stone had obstructed the right ureter ‘…in the past.’ Nothing now obstructed that kidney. But the slim gracile left collecting system outlined by white contrast material as it passed from the blood through the kidneys to the bladder in this old fashioned intravenous pyelogram shows what once the right side looked like which past obstruction has blunted and deformed.
Between the white blots and kidney’s edge lies less space on the right than on the left. That lessened space marks kidney tissue lost, and lost forever. Another IVP several years later showed no change for worse or better. Based on sequential measurements in 25 patients, these authors concluded that ‘lost and lost forever’, my phrase, applied universally. Things worsened nor improved after a loss from obstruction.
The tissue from an atrophic kidney, one far more advanced in loss than the one
pictured here, shows a bleak and barren emptiness that confirms the idea that
nephrons simply vanish, replaced by scar. This kidney was obstructed for many years and not by a stone but by a misplaced surgical ligature long forgotten.
Loss of Kidney Function
Let us place this case at one extreme and the young woman somewhere to its right, connoting a better outcome. At perhaps some point to the right, one finds cases where some recovery of function has been described after relief of obstruction, from stones or from strictures in the ureters. Renal function measured by radioisotope renograms increased on average when the blood flow to the obstructed side was at least 30% of that on the unobstructed side and the glomerular filtration at least 10 ml/min.
Kidney Disease in General from Stones
At the other pole, to the right, a vast majority of obstructing stones pass or are removed promptly and the kidney shows no measurable loss of size or function. Even so, stones link to kidney disease when one views large populations. In Olmsted County a higher fraction of 518 stone formers than 189 control subjects carried any diagnostic code for chronic kidney disease (CKD). Using the National Health and Nutrition Examination Survey (NHANES) III data set, we observed among overweight people lower estimated glomerular filtration rates among those who reported stone events.
Simply to reduce my listing of more reviews and primary articles, my colleague Anna Zisman recently published a thorough review of the links or not between stone forming and kidney disease. She concurs in the general opinion that stones can cause harm and stone formers have risk albeit very modest for the majority. Of special note, stones from systemic diseases seem more likely to injure kidneys than idiopathic stones.
What All This Means
A few simple doctrines shine out from all this detail.
Surgeons Monitor Stone Passage and Decide about Surgery
A stone that no longer hurts may still obstruct. Urological surgeons know this perfectly well and all patients need to is come for all follow up appointments and scans their surgeons suggest to follow the course of a stone. When to operate and when to let a stone pass requires a nice surgical judgment specific to any one patient and any one stone episode. Just because many patients read this site I hesitate to propose rules in place of such judgment for fear some – any – might try to substitute them for using their surgeons. As for surgeons who may read here, they can write this section better than I can.
Silent Obstruction Occurs and Destroys Kidneys
Because of this patients need considered wariness. Clues I wrote of above mean consultation with a physician. Suspicion warrants consultation. The cost of an extra image is nothing compared to a missed obstruction. An excellent research paper makes this point in numeric terms concerning postoperative imaging to exclude missed obstruction after ureteroscopy.
Screening For Systemic Causes of Stones Matters
Because stones from bowel disease, renal tubular acidosis, cystinuria, primary hyperparathyroidism and the like associate with lower long term kidney function they deserve special attention. This begins with recognition preferably at the first stone attack. My site has always emphasized the critical need for such diagnostic screening, which only physicians can implement. Once detected systemic causes require special physician attention and, unlike for the very common idiopathic stones, patients can do less for themselves with respect to fluids and diet.
Stone Prevention is Wise
Quite apart from miseries of pain and surgery, infection, bleeding, and all that attend on stones, prevention may protect kidney function. No trials support this idea nor can one imagine a trial mounted to ask it anymore. But evidence if suggestive should motivate all of us to pursue prevention.