Dear Editor,
The Consensus Conference Group recently published an article in Urolithiasis highlighting the importance of urine and stone analysis in the metabolic evaluation of kidney stone formers (KSF) [1]. Indeed, each kidney stone contains the imprints of the conditions which created them during their ‘lifetime in the kidney’.
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The morpho-constitutional classification method (MCC) established by Prof Michel Daudon correlates the morphological characteristics of stones with specific metabolic disorders [2]. Briefly, it distinguishes 7 types and 21 subtypes according to the crystalline composition and shape, color and structure of stones identified using an optical stereo-microscope (Table 1). This very specific method is easy to learn and provides the opportunity to quickly identify highly recurrent diseases, sometimes serious in their clinical consequences. Indeed, subtypes Ic, Ie, IIId, IVa2 and V are pathognomonic of specific clinical entities corresponding to primary hyperoxaluria type 1, enteric hyperoxaluria, hyperuricosuria with diarrhea, distal tubular acidosis and cystinuria, respectively. In 2019, the International COllaborative NEtwork on Kidney sTones (ICONEKT) encouraged medical community to integrate this method for rapid identification of disorders responsible for the highly recurrent diseases [3]. Despite growing evidence of the robust diagnostic value of Daudon’s MCC and its benefits in drawing up individualized treatment plans, this simple tool unfortunately still remains underexplored. Given the increasing prevalence of KSF and the worrying rise in cases in groups previously considered to be at lower risk of stones (for example, women and children), the aim of our “call to action letter” is to support the position of accurate stone analysis elegantly highlighted by the Consensus Conference that you recently published [1]. In this way, we hope to raise interest and encourage more physicians to consider Daudon’s MCC as a priority in their clinical practice in order to improve the care of KSFs.
Table 1
Daudon’s morpho-constitutional classification of kidney stones, main characteristics and corresponding etiologies
Type/subtype | Main component | Etiological orientation |
|---|---|---|
Ia | Whewellite | Dietary hyperoxaluria, low diuresis, intermittent moderate hyperoxaluria, Randall’s plaque |
Ib | Whewellite | Stasis, low diuresis, crystalline conversion from weddellite to whewellite |
Ic | Whewellite | Primary hyperoxalurias (mainly AGXT type 1 mutation) |
Id | Whewellite | Malformative uropathy, stasis and confined multiple stones |
Ie | Whewellite | Enteric hyperoxaluria, inflammatory (Crohn disease), ileal resections, chronic pancreatitis |
IIa | Weddellite | Hypercalciuria with high calcium/citrate ratio |
IIb | Weddellite | Hypercalciuria ± hyperoxaluria ± hypocitraturia, stasis, low diuresis |
IIc | Weddellite | Hypercalciuria + malformative uropathy + stasis and confined multiples stones |
IIIa | Uric acids anhydrous | Low urine pH, intermittent high uric acid, urine stasis, prostate hypertrophy |
IIIb | Uric acid dihydrate ± uric acid anhydrous Urate salts |
Low urine pH (metabolic syndrome, type 2 diabetes mellitus), high urinary uric acid, ammoniogenesis defect, hyperuricemia, myelo- and lymphoproliferative disorders |
IIIc | Ammonium hydrogen urate | High urinary urate, alkaline urine pH |
IIId | Ammonium hydrogen urate | High urinary urate, alkaline urine pH, malnutrition, low phosphate intake, excessive ammoniagenesis (infectieuse-urinary tract infection by urea-splitting micro-organisms or nutritional) Chronic diarrhea, electrolytes and alkali loss, low phosphate intake, laxative abuse, anorexia |
IVa1 | Carbapatite | Hypercalciuria, urinary tract infection see carbonatation rate of carbonated calcium phosphate |
IVa2 | Carbapatite | Inherited or acquired distal renal tubular acidosis, Sjogren syndrome, medullary sponge kidney |
IVb | Carbapatite + other calcium phosphates (± struvite) | Urinary tract infection, hypercalciuria, primary hyperparathyroidism |
IVc | Struvite | Urinary tract infection by urea-splitting bacteria |
IVd | Brushite | Hypercalciuria, primary hyperparathyroidism, phosphate leak, |
Va Vb | Cystine Cystine | Cystinuria Cystinuria + inadequate diet and/or medical management + stasis |
VIa VIb VIc | Proteins Proteins + drugs or metabolic compounds Proteins + whewellite | Urinary tract infection, chronic pyelonephritis Example of drug-induced stone (mixture of proteins and atanazavir) End stage renal failure + relatively high urinary calcium concentration (long term calcium and Vitamin D therapy) |
VII | Miscellaneous |
Declarations
Conflict of interest
The authors declare that they do not have conflict of interest.
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