Spontaneous hypercalcemia in patients undergoing dialysis. Etiologic and therapeutic considerations

Acute severe hypercalcemia after traumatic fractures and immobilization in hypophosphatasia complicated by chronic renal failure

CONTEXT

Hypophosphatasia (HPP) features deficient activity of the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP) due to loss-of-function mutation(s) within the TNSALP gene. Consequently, inorganic pyrophosphate, a TNSALP substrate and inhibitor of mineralization, accumulates extracellularly. This can cause rickets or osteomalacia.

OBJECTIVE

We report a 55-year-old man with HPP and chronic renal failure (CRF) requiring hemodialysis who developed severe hypercalcemia acutely after traumatic fractures and immobilization. He manifested HPP in childhood and in middle age received hemodialysis for CRF attributed to hypertension and anti-inflammatory medication. He took 2 g of calcium carbonate orally each day to bind dietary phosphorus, but never aluminum hydroxide or any form of vitamin D. Pretrauma serum levels of calcium spanned 8.4-10.7 mg/dL (normal [Nl], 8.6-10.3), inorganic phosphate 5.8-6.4 mg/dL (Nl, 2.5-4.5), and PTH 63-75 pg/mL (Nl, 10-55).

RESULTS

Rapid succession falls fractured multiple major bones. Six hours later, he became confused. Serum calcium was 14.9 mg/dL, ionized calcium was 7.4 mg/dL (Nl, 4.5-5.1), and PTH was 16 pg/mL. Hemodialysis quickly corrected his hypercalcemia and confusion. Low serum alkaline phosphatase persisted, and follow-up skeletal histopathology showed that his osteomalacia was severe.

CONCLUSION

Hemodialysis does not heal the skeletal disease of HPP. During sudden fracture immobilization in HPP, sufficient calcium can emerge from bone, perhaps from a rapidly exchangeable calcium pool, to cause acute severe hypercalcemia if the kidneys cannot compensate for the mineral efflux. Hence, we worry that acute hypercalcemia might accompany sudden immobilization in CRF patients without HPP if they have adynamic bone disease.

Is 24,25(OH)D level really high in dialysis patients with high FGF23 levels?

Deficiency of 1,25-dihydroxyvitamin D [1,25(OH)(2)D] and excessive fibroblast growth factor (FGF23) are suggested to be associated with increased mortality in patients with chronic kidney disease (CKD). Generally, 24-hydroxylation has been considered the first step in the degradation pathway of 1,25(OH)(2)D and 25(OH)D. 24,25-dihydroxyvitamin D [24,25(OH)(2)D] was believed to be a degradation product, with no important biological effects. However, some data have accumulated showing that 24,25(OH)(2)D has biological effects on its own. Under conditions of eucalcemia, the synthesis of 24,25(OH)(2)D is increased, and the synthesis of 1,25(OH)(2)D is decreased. In patients with CKD, both high parathyroid hormone levels, which decrease the activity of enzyme CYP24A1 (24-hydroxylase), and high FGF23 levels, which increase the activity of enzyme CYP24A1, were often detected. However, information about 24,25(OH)(2)D levels in these patients is very limited. Whether compensatory changes in levels of FGF23 and 24,25(OH)(2)D in CKD patients are protective or harmful remain unknown issues. Therefore, more studies are needed to identify the nature of the interactions between these molecules and to fully elucidate their clinical significance.

Aluminium intoxication in renal disease

Aluminium intoxication in renal failure occurred over weeks or months when dialysis fluid or parenteral solutions were heavily contaminated and over many years when the main source was oral administration of aluminium-containing phosphate binders. Encephalopathy was common during subacute intoxication but in slow aluminium poisoning the main brunt was borne by the bones. However, in both tempos of intoxication several organs or systems were involved. Encephalopathy was usually accompanied by bone disease, bone disease by parathyroid suppression and both by anaemia. The heart and the lymphocytes are probably damaged by aluminium overload. Among the many questions left unanswered 15 years after the incrimination of aluminium as the cause of this multi-system illness are: (1) does low level aluminium overload in renal failure cause gradual deterioration in cerebral function? And, if so, (2) does it resemble Alzheimer's disease or a slow-onset version of dialysis encephalopathy? The evidence we review suggests that the answer to (1) is 'yes' and to (2) 'probably the latter'.

Symptomatic hypercalcemia in a diabetic patient undergoing continuous ambulatory peritoneal dialysis: value of bone biopsy in the diagnosis and management

An elderly man with diabetes mellitus and end-stage renal disease managed with continuous ambulatory peritoneal dialysis (CAPD) was hospitalized with peripheral vascular insufficiency; he developed hypercalcemia and became mentally obtunded. Lowering dialysate Ca from 3.5 mEq/L to 2.5 mEq/L, stopping calcium acetate, and ultimately hemodialysis with calcium-free dialysate did not lead to reversal of the hypercalcemia or improvement of his symptoms. The intact parathyroid hormone PTH level was 187 pg/mL, a value rarely associated with significant osteitis fibrosa. A search for other causes of hypercalcemia was unrevealing, and a iliac crest bone biopsy was done. The latter showed osteitis fibrosa, and the patient underwent parathyroidectomy. The hypercalcemia reversed quickly, and his mental symptoms slowly improved. The discussion reviews the probable causes of hypercalcemia in diabetic patient undergoing CAPD with 3.5 mEq/L dialysate calcium and using calcium-containing phosphate binders, with hyperparathyroidism certainly not the usual cause. The reason for the occurrence of significant hyperparathyroidism in the face of only modest elevation of PTH is considered. The value of bone biopsy in resolution of this problem is apparent.

Diagnosis and management of bone disorders in chronic renal failure and dialyzed patients

Renal osteodystrophy is multifactorial. Decreased calcium absorption from the GI tract, secondary to low calcitriol levels; hyperphosphatemia; skeletal resistance to the action of parathormone; and aluminum deposition on the surface of the bones are its main pathogenetic mechanisms. Its biochemical features include abnormalities in serum calcium, phosphate, alkaline phosphatase, parathormone, calcitriol, and aluminum concentration. Radiographic methods are of little use in the characterization of the type of osteodystrophy present, but they may be of help in assessing mineral loss from the skeleton. Clinical manifestations are from bones (pain, deformities, fractures) or from metastatic calcifications. Bone biopsy is the definitive means of diagnosis. The main histologic types of osteodystrophy include osteitis fibrosa, osteomalacia, mixed form (with features of both osteitis fibrosa and osteomalacia), and aluminum osteodystrophy (presenting as either osteomalacia or aplastic lesion). The management of renal osteodystrophy should address all the pathogenetic mechanisms. Correction of the abnormalities in calcium and phosphate metabolism and prevention of aluminum osteodystrophy are the cardinal rules of management. Specific measures (parathyroidectomy, chelation of aluminum) have clear-cut indications and usually require a bone biopsy.

Polycystic kidneys do maintain good endocrine function

We develop here the hypothesis that polycystic kidneys (PCK) may maintain, to a certain extent, the ability to perform endocrine functions. We know that patients with adult polycystic kidney disease (APCKD) produce more erythropoietin and maintain a higher hematocrit than patients with other primary diseases of the kidneys. It is possible that they synthesize more 1,25 and 24,25 Vit D3 and metabolize better the parathyroid hormone and other hormones. If it is correct, they may have fewer signs of secondary hyperparathyroidism and less bone marrow fibrosis which along with increased erythropoietin production would explain the higher hematocrit.

Parenteral calcitriol for treatment of severe renal osteodystrophy in children with chronic renal insufficiency

Renal osteodystrophy is a common and incapacitating complication of chronic renal failure in children. Standard therapy with oral calcium supplements, phosphate binders, and vitamin D preparations is often inadequate to control progressive bone disease. We report the use of parenteral calcitriol therapy in two children, aged 2 and 15 years, respectively, with chronic renal failure. This treatment effectively suppressed secondary hyperparathyroidism in both patients, causing a nearly 50% reduction in circulating parathyroid hormone level and a parallel decline in serum alkaline phosphatase activity. In the younger patient, therapy was associated with healing of subperiosteal bone resorption and accelerated growth velocity. These findings indicate that parenteral administration of calcitriol may be an effective treatment option in some patients with refractory renal osteodystrophy and secondary hyperparathyroidism.