[Epidemiological, clinical and evolutionary particularities of primary distal tubular acidosis in Tunisian children]. / Particularités épidémiologiques, cliniques et évolutives de l'acidose tubulaire distale primitive chez l'enfant tunisien.

INTRODUCTION: The distal renal tubular acidosis of children is characterized by hyperchloremic metabolic acidosis with normal anion gap, hypokalemia, hypercalciuria and nephrocalcinosis. It is secondary to the inability of alpha intercalar cells of the distal tubule to acidify urine of genetic origin. OBJECTIVE: To analyse the epidemiological aspects of distal tubular acidosis in Tunisia and study its evolutionary profile. PATIENTS AND METHODS: We conducted a retrospective descriptive study involving 44 patients followed at the paediatrics department of the Charles Nicolle Hospital in Tunis for 28 years (1991-2018). RESULTS: The most common discovery circumstances were growth retardation (88.6%), dehydration (56.8%), ployuro-polydipsic syndrome (47.7%), vomiting (40.9%) and nephrocalcinosis (38.6%). Growth retardation was found in 52.3% of patients. Dehydration was diagnosed in 59.1% of patients on the first exam. Polyuria was constant with an average diuresis of 8 cc/kg/h. All patients had the complete form of distal renal tubular acidosis with an average alkaline reserve of 11.1 mmol/L. Nephocalcinosis was found in 77.3% associated with nepholithiasis in 22.7%. Twenty-four patients had sensorineural deafness, nine of whom had ATP6V1B1/2p13 mutation. The ATP6V0A4/7q33-34 mutation was present in two patients. We used a high alkaline treatment dose with an average maintenance dose of 8.17 mmol/kg/24 hours. In the long term, stunting persisted in 34% of patients. The mean of creatinine's clearance at the last evaluation was 89.38 mL/min/1.73 m2 SC with stage 2 of chronic kidney disease in 50% of patients. CONCLUSION: Distal renal tubular acidosis has long been considered a benign pathology but is responsible for a progressive decline in GFD. Adequate metabolic control is needed to stabilize kidney function.

[A complex case of renal phosphate wasting ]. / Une fuite rénale de phosphates complexe .

We describe here the case report of a young man of 34-years old suffering from a haemorrhagic rectocolitis and presenting with marked hypophosphatemia secondary to an infusion of ferric-carboxymaltose. The renal phosphate wasting was asserted by a very low renal maximal reabsorption rate of phosphate associated with a high plasma FGF-23 level. Three months later we explored the patient and his father since we learnt that both of them had suffered from kidney stones for years with marked hypercalciuria. Kidney stones were composed of weddellite and carbapatite. We suspected a familial phosphate renal wasting syndrome but however no mutation of the renal phosphate carriers could be identified.

[Nephrocalcinosis in children]. / Néphrocalcinose de l'enfant.

Nephrocalcinosis is defined by calcium phosphate or calcium oxalate deposits in the kidney parenchyma, particularly in tubular epithelial cells and interstitial tissue. It should be differentiated from urolithiasis where calcium salts deposits are located in the kidney and urinary tract. The epidemiology of nephrocalcinosis in children is unknown but the condition is not so rare, with an increased incidence in preterm infants. Often detected as an incidental finding, nephrocalcinosis may be classified according to the radiological type: medullary, cortical or diffuse. Nephrocalcinosis in children can be caused by a variety of etiology. The most common causes concern medullary nephrocalcinosis and include hereditary tubular disorders, in particular distal renal tubular acidosis and Dent disease, metabolic disorders such as idiopathic hypercalciuria and hyperoxaluria, and iatrogenic causes such as vitamin D intoxication. In the newborn, the main cause is hypercalciuria of the premature baby, whose multifactorial origin is largely iatrogenic. Primary hyperoxaluria which can lead to early onset nephrocalcinosis and usually to chronic kidney disease should always be considered and further investigated. In order to provide a specific diagnosis, it is essential to take into account the family history, the clinical context and complete laboratory data. Early initiation of an appropriate etiological treatment is recommended and may prevent or delay the progression to chronic kidney disease in some cases.

[Pathogenic factors in calcium oxalate stones: Epidemiological investigation]. / Recherche de facteurs lithogènes au cours des lithiases oxalo-calciques : enquête épidémiologique.

INTRODUCTION: Calcium oxalate stones are the most common urolithiasis. Changes in dietary habits, socio-economic and health status of populations explain its progression. The aim of our study was to determine metabolic factors leading to lithiasis and clarify its causes. PATIENTS AND METHODS: This is a retrospective study of 100 patients with calcium oxalate stones identified by morpho-constitutional study, collected in our department over a period of 5 years (2008-2013). We analyzed clinical, radiological and metabolic data. RESULTS: They were 73 men and 27 women (gender ratio: 2.7), aged meanly of 44.8 years. Dietary survey revealed inadequate calcium intake in 87% of cases. Urinary abnormalities were hypocitraturia (34%), hypomagnesuria (32%) and outflow hypercalciuria (21%). Crystalluria was positive in 44% of cases. Whewellite was the most common crystalline form. Calculi were bilateral (53%), renal (85%) and mainly collected after urological procedures (74%). Infrared analysis showed that 81% of stones have a heterogeneous composition. Pure Whewellite or combined with other compounds was the most frequent (31%). Idiopathic calcium oxalate lithiasis was the most common etiology (69%). Among secondary etiologies, diabetes was most frequently found (10%). CONCLUSION: Our epidemiological study of calcium oxalate stones has allowed us to identify the high frequency of food hyperoxaluria partly explained by a low calcium intake and a diet rich in oxalate phytotherapy. LEVEL OF EVIDENCE: 4.

How to manage an isolated elevated PTH?

The aim of this article is to discuss the diagnostic approach of an increased serum PTH concentration in a normocalcemic, normophosphatemic patient. Detection of this biological presentation is frequent in routine practice all the more that PTH reference values established in vitamin D replete subjects with a normal renal function are used by the clinical laboratories. The first step in this diagnostic approach will be to rule out a cause of secondary hyperparathyroidism (SHPT). Among these, the most frequent are vitamin D deficiency, very low calcium intake, impaired renal function, malabsorptions, drugs interfering with calcium/bone metabolism, such as lithium salts and antiresorptive osteoporosis therapies, hypercalciuria due to a renal calcium leak. If no cause of SHPT are evidenced, the diagnosis of normocalcemic primary hyperparathyroidism (PHPT) should be considered. A calcium load test is a very useful tool for this diagnosis if it shows that serum PTH is not sufficiently decreased when calcemia rises frankly above the upper normal limit. In a normocalcemic patient with hypercalciuria and a high serum PTH concentration, a thiazide challenge test may help to differentiate SHPT due to a renal calcium leak from normocalcemic PHPT. Beyond the discussion of this diagnostic flowchart, we also discuss some points about the merits and the difficulties of measuring and interpreting ionized calcemia and 24-h calciuria.