Parathyroid hormone secretion in familial vitamin-D-resistant rickets

Tertiary hyperparathyroidism attributable to long-term oral phosphate therapy

OBJECTIVE

To report a rare case of tertiary hyperparathyroidism (HPT) as a result of long-term oral phosphate therapy.

METHODS

We present a case report, with a focus on clinical manifestations and biochemical findings during the course of tertiary HPT, and discuss the pathophysiologic features of this disorder and the therapeutic strategies.

RESULTS

A 35-year-old woman, 22 years after the initial diagnosis of familial hypophosphatemic rickets and initiation of treatment with phosphate and vitamin D, underwent assessment for recurrent symptomatic kidney stones, bone pain, and fatigue. Laboratory studies performed 10 months before this presentation showed findings consistent with secondary HPT. Examination was notable for short stature, and pertinent laboratory results were as follows: intact parathyroid hormone 602 pg/mL, calcium 10.9 mg/dL, and phosphorus 3.6 mg/dL. Tertiary HPT was diagnosed, and she underwent subtotal parathyroidectomy and transcervical thymectomy. Postoperatively, she had hypocalcemia and was treated with calcitriol, phosphate, and calcium carbonate; the last agent was discontinued when the serum calcium normalized. Despite multiple dosage alterations in the phosphate and calcitriol therapy, the patient had recurrent tertiary HPT and another kidney stone (treated by lithotripsy). Three years after the subtotal parathyroidectomy, treatment consisted of cinacalcet, calcitriol, and elemental phosphate.

CONCLUSION

Long-term follow-up of patients with tertiary HPT is critical, with careful dosage adjustments in phosphate and vitamin D therapy and monitoring of serum levels of phosphorus, calcium, and parathyroid hormone.

Prolonged high-dose phosphate treatment: a risk factor for tertiary hyperparathyroidism in X-linked hypophosphatemic rickets

OBJECTIVE

X-linked hypophosphatemic rickets is characterized by renal phosphate wasting, hypophosphatemia and defective bone mineralization. Treatment with oral phosphate (Pi) and calcitriol improves skeletal changes but associates with secondary hyperparathyroidism and nephrocalcinosis. Tertiary hyperparathyroidism is a rare complication of the treatment. The aim of the present study was to identify treatment-related factors that might be associated with the transition of secondary hyperparathyroidism to tertiary hyperparathyroidism in patients with X-linked hypophosphatemic rickets.

DESIGN

Thirteen patients with X-linked hypophosphatemic rickets and secondary or tertiary hyperparathyroidism were included in the study. Their hospital records were reviewed and compared for onset, duration and dosage of treatment, and for age of diagnosis and degree of secondary hyperparathyroidism.

RESULTS

Two patients developed tertiary hyperparathyroidism and 11 patients secondary hyperparathyroidism during the treatment. Patients with tertiary hyperparathyroidism had, on average, earlier onset and longer duration of treatment, higher dose of Pi and longer duration of treatment with very high Pi doses (> 100 mg/kg/day) compared to the 11 patients with secondary hyperparathyroidism. However, variation of all parameters was great with considerable overlap. Very high S-PTH levels > or = 42 pmol/l were observed in those who later developed tertiary hyperparathyroidism.

CONCLUSIONS

Prolonged very high dose oral Pi treatment is a major risk factor for the development of tertiary hyperparathyroidism in X-linked hypophosphatemic rickets.

Tertiary hyperparathyroidism after high-dose phosphate therapy in adult-onset hypophosphatemic osteomalacia

OBJECTIVE

To describe a case of adult-onset hypophosphatemic osteomalacia treated with orally administered phosphate and complicated by tertiary hyperparathyroidism.

METHODS

We present pertinent clinical, radiologic, and laboratory details of the study patient for a period of more than 20 years and discuss the few reported cases of tertiary hyperparathyroidism attributable to prolonged phosphate therapy.

RESULTS

A 49-year-old Jordanian man, who had been diagnosed at age 26 years as having sporadic adult-onset hypophosphatemic vitamin D-resistant osteomalacia, presented with severe right hip pain, severe osteopenia with lytic bone lesions, and hypercalcemia after prolonged oral treatment with phosphate and vitamin D. These clinical, radiologic, and biochemical findings, in conjunction with a very high serum parathyroid hormone level, indicated the diagnosis of tertiary hyperparathyroidism, which was substantiated histopathologically.

CONCLUSION

Physicians should be aware of the potential for development of tertiary hyperparathyroidism in patients receiving prolonged oral phosphate therapy.

Medical management and complications of X-linked hypophosphatemic vitamin D resistant rickets

To improve the growth failure, bowed legs, and biochemical and radiological abnormalities in patients with X-linked hypophosphatemic vitamin D resistant rickets (XLH), combined therapy of phosphate and calcitriol is the best therapeutic approach at present. However, the complications involving combined therapy, such as hypercalcemia, nephrocalcinosis and hyperparathyroidism, are not fully solved. To achieve better control, new therapeutic approaches have been reported recently, for example, growth hormone (GH) or new vitamin D analogs. GH improved linear growth, decreased phosphate reabsorption and increased 1-alpha-hydroxylase activity. Furthermore, 24R,25-dihydroxyvitamin D3 (24,25) improved the bone lesions in hypophosphatemic (Hyp) mice, and also in XLH, without the adverse effects such as hypercalcemia or hypercalciuria compared with 1,25-dihydroxyvitamin D3. These new approaches should be considered for the treatment of patients with XLH.

Autonomous hyperparathyroidism in X-linked hypophosphataemia

Four patients with familial hypophosphataemic rickets developed significant hypercalcaemia which persisted after discontinuation of vitamin D therapy. They had increased PTH levels and were operated for hyperparathyroidism at the ages of 18, 20, 24 and 45 years, respectively. Three of the patients had previously received phosphate treatment and one patient developed hyperparathyroidism 7 years after treatment with calcitriol. Histological evaluation revealed different degrees of parathyroid hyperplasia in all patients, with persistently increased PTH and/or calcium levels after surgery. The possibility of autonomous hyperparathyroidism should be evaluated in the follow-up of patients with X-linked hypophosphataemic rickets.

An unusual giant cell lesion in a child with vitamin D-resistant rickets

This paper reports the presence of a focus of giant cells in a sinus tract associated with an abscessed primary tooth in a patient with vitamin D-resistant rickets. The relevance of this giant cell lesion to the systemic disorder is discussed.

Acute effects of calcitriol and phosphate salts on mineral metabolism in children with hypophosphatemic rickets

We investigated the acute effects of oral administration of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and phosphate on the major mineral metabolism indexes in six children with vitamin D-resistant rickets treated with a long-term regimen of phosphate and calcitriol. Two acute tests were performed in which plasma calcium, phosphate, immunoreactive parathyroid hormone (iPTH) (intact molecule), 25-hydroxyvitamin D (25-OHD), and 1,25-(OH)2D levels were measured: the first after an oral phosphate load (20 mg/kg) was administered after calcitriol had been discontinued for 10 days, and the second after a calcitriol load (0.03 microgram/kg) plus the same phosphate load but with the children receiving the usual combination treatment. There were no significant differences in basal levels of calcium, phosphate, iPTH, 25-OHD, or 1,25-(OH)2D between the two tests, nor were delta percent calcium and 25-OHD values significantly different. The delta percent plasma phosphate concentration at 60 minutes was significantly higher during test 2 than during test 1 (p less than 0.01) and delta percent iPTH concentration at 60 minutes was significantly higher during test 1 than during test 2 (p less than 0.01). In test 2 the iPTH level returned to baseline at 180 minutes. Higher delta percent 1,25-(OH)2D values at 60 minutes were observed in test 2 than in test 1 (p less than 0.01). Furthermore, the delta percent 1,25-(OH)2D levels were still higher at 180 minutes in test 2 than during test 1 (p less than 0.01). Our study indicates that oral calcitriol has an inhibitory effect on iPTH secretion in the hours immediately after oral phosphate administration in children with vitamin D-resistant rickets.

Recent advances in pediatric metabolic bone disease: the consequences of altered phosphate homeostasis in renal insufficiency and hypophosphatemic vitamin D-resistant rickets

Over the past decade our understanding of the pathogenesis of altered mineral homeostasis in chronic renal failure (CRF) and X-linked hypophosphatemic vitamin D-resistant rickets (XLH) has increased, and has provided a rational approach for the use of the 1 alpha-hydroxylated analogues of vitamin D in their therapy. Recent evidence suggests that intracellular phosphate (Pi) retention in CRF plays a major role in decreasing serum 1,25-dihydroxyvitamin D (1,25(OH)2D) levels, which are responsible for the progressive rise in serum parathyroid hormone (PTH) concentrations through the direct action of 1,25(OH)2D on the parathyroid gland. 1,25(OH)2D levels affect the number of intracellular 1,25(OH)2D receptors, preproPTH mRNA levels and the set point for calcium suppression of PTH release. Further in experimental CRF, the maintenance of normal 1,25(OH)2D levels prevents parathyroid gland hyperplasia. These studies indicate that depressed renal 1 alpha-hydroxylase activity due to Pi retention is a major factor in directly increasing PTH secretion, which in turn contributes significantly to the severity of renal osteodystrophy. Thus the aim of therapy in early CRF should be to maintain normal levels of 1,25(OH)2D which can be achieved by either dietary Pi restriction and oral Pi binders or by administering small doses of 1 alpha-hydroxylated metabolites. The long term consequences of these two different therapeutic regimens still need to be assessed. In XLH, evidence is rapidly accumulating that alterations in 1 alpha-hydroxylase activity secondary to impaired Pi handling by the proximal renal tubule, results in decreased serum 1,25(OH)2D levels, which might be responsible for a number of the associated abnormalities documented in both treated and untreated XLH patients. These abnormalities include decreased calcium and Pi absorption by the intestine and low normal serum calcium values. In vitamin D- and Pi-treated patients 1,25(OH)2D levels are further depressed, with a resultant increase in PTH values, and the development of tertiary hyperparathyroidism in a small number of patients. The use of 1 alpha-hydroxylated analogues rather than vitamin D together with Pi supplements decreases the severity of hyperparathyroidism, improves Pi absorption from the intestine and markedly ameliorates the degree of osteomalacia. Whether long-term therapy with these analogues will prevent the development of tertiary hyperparathyroidism in patients with XLH is unclear.

Familial hypophosphataemic rickets: experience with 24 children from Kuwait

Between 1982 and 1988, familial hypophosphataemic rickets (FHR) was diagnosed in 24 children, in nine during screening of the families of index patients. The average annual incidence was 0.2/1000 live births. There were 16 boys and 8 girls in 10 families, of which nine had more than one affected child. Their ages at the onset of the disease ranged between 10 months and 14 years (mean 6.9 yrs). Growth retardation and bowing of the legs were the most prominent features, observed in all index patients and in four of the patients diagnosed by screening. Treatment with 1 alpha-hydroxyvitamin D3 and phosphates was associated with acceleration of growth in all children, healing of rickets in 21, and normalization of the serum phosphate in 22. Two children with late diagnosis are now older than 16 years with a final height below the 3rd centile. Three more pubertal children are also shorter than the 3rd centile. In areas where nutritional rickets is common, FHR is likely to be missed and the treatment delayed with grave consequences; in particular, growth retardation and bone deformity.

Abnormal parathyroid function in the X-linked hypophosphatemic mouse

Employing a cytochemical bioassay, we compared parathyroid function in normal and X-linked hypophosphatemic (Hyp) mice. Under basal conditions Hyp mice manifested hypocalcemia and, in accord, had a plasma bioactive parathyroid hormone concentration (3.04 +/- 0.14 pg/ml) significantly greater than that of normals (2.16 +/- 0.14 pg/ml). We confirmed the validity of the bioassay by demonstrating that the plasma collected from both mouse models diluted parallel to the assay standard curve. Moreover, after parathyroidectomy, normal and Hyp mice had plasma bioactive parathyroid hormone levels approximately 90% less than those obtained under basal conditions and indistinguishable from one another. In further studies we observed that dietary calcium and/or vitamin D deprivation in both animal models resulted in a comparable decline of the plasma calcium concentration. However, the concordant increase of the circulating bioactive parathyroid hormone level was greater in the normal mice. Thus, the bioactive parathyroid hormone concentration obtained in response to a low calcium challenge in normals was significantly greater than that in Hyp mice. In contrast, in response to dietary calcium loading, the plasma bioactive parathyroid hormone levels did not decrease significantly from basal values in either animal model. These data illustrate that the bioactive parathyroid hormone concentration in both normal and Hyp mice is inversely correlated with the plasma calcium. However, while the Hyp mice maintain an elevated plasma parathyroid hormone concentration under basal conditions (in response to a decreased plasma calcium), the parathyroid activity of the mutants after a more severe hypocalcemic challenge is attenuated, resulting in a significantly different model of linear correlation. Thus, these data indicate that Hyp mice manifested abnormal regulation of parathyroid function.

Development of hypercalcemic hyperparathyroidism after long-term phosphate supplementation in hypophosphatemic osteomalacia. Report of two cases

Orally administered phosphate supplements are the mainstay of therapy for hypophosphatemic osteomalacia of diverse causes and are generally believed to be free from harmful side effects. Two cases are reported, however, in which long-term therapy (14 and 10 years, respectively) resulted in hypercalcemic hyperparathyroidism associated with surgically proved adenomatous hyperplasia. This complication occurred despite concomitant treatment with pharmacologic doses of vitamin D. Thus, long-term oral phosphate therapy can produce tertiary hyperparathyroidism in susceptible patients.

Primary hyperparathyroidism: four- to eight-year postoperative follow-up demonstrating persistent functional insignificance of microscopic parathyroid hyperplasia and decreased autonomy of parathyroid hormone release

Thirty-nine patients with primary hyperparathyroidism were studied four to eight years after their initial operation. In six patients, both the pathologist and surgeon agreed on the diagnosis of solitary adenoma; in 16 patients, the surgeon diagnosed solitary adenoma and the pathologist parathyroid hyperplasia (microscopic hyperplasia). In 16 patients, primary chief cell hyperplasia was agreed upon by the pathologist and surgeon. In the 16 patients with microscopic hyperplasia, there have been no long-term recurrences of hypercalcemia, but, in two patients, plasma parathyroid hormone levels are high. Parathyroid hormone--total calcium regression curves demonstrate significant preoperative correlation in solitary adenoma, p less than 0.01, and primary chief cell hyperplasia, p less than 0.05. After operation, significant correlations were not found between parathyroid hormone and total calcium. T-testing slope differences of pre- and postoperative parathyroid hormone--total calcium regression curves demonstrates a significant (p less than 0.01) shift to the right of the microscopic hyperplasia patients after operation, moving them to a broader range of total calcium per picogram parathyroid hormone. We conclude that 1) in primary hyperparathyroidism, positive regulation of total calcium by autonomously released parathyroid hormone exists in patients with solitary adenoma and chief cell hyperplasia; 2) autonomously functioning parathyroid tissue has been removed by operation for solitary adenoma with coexistent microscopic parathyroid hyperplasia. In this four- to eight-year follow-up period, it is clear that microscopic parathyroid hyperplasia is not associated with recurrent hypercalcemia. Two functionally distinct forms of parathyroid suppression are suggested; positively regulated microscopic hyperplasia and negatively regulated pathologically suppressed glands.

Total ionized serum calcium and parathyroid hormone levels in patients with disseminated coccidioidomycosis

Twenty-one patients with severe coccidioidomycosis, including eight with osseous lesions, were admitted to the University of California, Davis, Medical Center, during a recent epidemic. Transient mild ionized hypercalcemia occurred in only two patients, and a tendency toward low normal ionized calciums was noted. Parathyroid hormone levels appeared to be appropriate for the ionized calcium in these patients. There were no significant differences in ionized calcium levels of parathyroid hormone levels among patients with and without osseous coccidioidomycosis. We conclude that hypercalcemia is rare in coccidioidomycosis, even with extensive bony involvement.

Hypercalcemia in the accelerated phase of chronic myelogenous leukemia

Within a recent one-year period, 3 patients in the accelerated phase of chronic myelogenous leukemia were admitted to our medical center with severe hypercalcemia. Simultaneous determinations of ionized calcium and parathyroid hormone levels in 2 of the patients confirmed the hypercalcemia and revealed suppression of parathyroid hormone. We conclude that hypercalcemia in the accelerated phase of chronic myelogeneous leukemia may be more common than previously described and is not mediated by parathyroid hormone. An elevated parathyroid hormone level accompanying hypercalcemia in these patients should suggest the additional diagnosis of primary hyperparathyroidism. Mithramycin was necessary for control in 2 of our cases as well as in others reported in the medical literature and should be an early therapeutic consideration whenever saline diuresis is inadequate.

Spinal canal stenosis in adult with hypophosphataemic vitamin D-resistant rickets

A case is described of a 55-year-old male with hypophosphataemic vitamin D-resistant rickets, who presented with long-standing back pain and paraesthesiae in both legs considered to be due to osteoid encroachment on an already narrow spinal canal. Marked symptomatic improvement has followed extensive lumbar laminectomy.

The response to 1,25-dihydroxycholecalciferol and to dihydrotachysterol in adult-onset hypophosphataemic osteomalacia

The biochemical changes observed in a patient with adult-onset hypophosphataemic osteomalacia after three weeks treatment with 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) followed by dihydrotachysterol (DHT) are reported. The treatment with 1,25-(OH)2D3 resulted in restoration of intestinal phosphate absorption to normal with a small rise in plasma phosphate concentration; there was no significant change in tubular reabsorption of phosphate. The tubular reabsorption of bicarbonate, which was initially low, returned almost into the normal range with normalisation of plasma bicarbonate concentration. Aminoaciduria decreased. There were no changes in plasma or urinary calcium but immunoreactive parathyroid hormone (i-PTH) which was initially elevated fell but still remained above the normal range. These changes were maintained after replacing the 1,25-(OH)2D3 treatment with dihydrotachysterol (DHT).

Phosphorus deficiency, parathyroid hormone and bone resorption in the growing rat

Sham-operated and parathyroidectomized (PTX) rats were divided into two pair-fed groups, one on a normal mineral intake (0.5% Ca, 0.3% P), the other on a regimen low in phosphorus (0.5% Ca, 0.03% P). P depletion led to a drop in plasma P and urine P, a rise in plasma Ca and a marked rise in urine Ca, a drop in serum magnesium and a rise in urine Mg. The changes were more pronounced in the PTX animals, but final values were the same in both groups. Parallel bone-seeking isotope (85Sr, 177Lu, 237Np) studies in nonablated animals revealed an increase in the urinary nuclide output and in the urine/tibia ratio in P-deficient animals. Normal and primary bone osteocytes decreased and enlarged osteocytes increased as a result of P deficiency; osteoclasts and osteoblasts also increased. Bone composition showed a drop in ash content and a rise in water, with a light decrease in both Ca and P, and a corresponding rise in hydroxyproline and nitrogen in the P-deficient animals. The results are interpreted to mean that P-deficiency in the young growing rat leads to an increase in bone resorption which occurs also in the absence of parathyroid hormone (PTH). The fact that final values were similar in the control and PTX P-deficient animals suggests that steady-state regulation can also occur without PTH. Because P-deficiency leads to rapid hypercalcemia and rapid marked hypercalciuria, there may exist a mechanism for phosphate regulation which would then supersede Ca homeostasis. The change in serum and urine Mg levels may reflect a decrease in tubular Ca and Mg reabsorption associated with P-deficiency.

Recessive hypophosphataemic rickets, and possible aetiology of the 'vitamin D-resistant' syndrome

Two out of 3 children of a first-cousin marriage presented with severe rickets in infancy and are now adult. Their disease has shown continued activity, marked resistance to treatment with vitamin D, early fusion of cranial sutures, greatly increased bone density, nerve deafness, and life-long hypophosphataemia unaffected by treatment. Both parents and a third sib were normal clinically and biochemically. Blood grouping supported both stated paternity and parental consanguinity. Genetics of this unique disease can only be explained satisfactorily on the basis of autosomal recessive transmission, a mode not previously reported in primary hypophosphataemia. This homozygous disease resembles an exaggerated form of common X-linked rickets, though it is caused by a different gene. Although rare, it is particularly important because of the information it provides on the pathogenesis of both forms. We propose that both syndromes may result from multiple target organ unresponsiveness to 1,25-dihydroxycholecalciferol in intestine, kidney, bone, and parathyroid gland.

Parathyroid function tests with EDTA infusions in infancy and childhood

To determine the functional capabilities of the parathyroid glands, 17 EDTA infusions were given to 11 children (ages 1 month to 12 years) and to two mothers of four of the children. Serum ionized Ca fell from 4.1 mg/dl to 3.4 mg/dl. Excessive parathyroid hormone responses were elicited during seven of nine EDTA infusions in five children and in one adult with hypophosphatemic rickets, during the active phase of rickets. In four of five subjects with problems related to hypercalcemia, borderline low or undetectable PTH responses were elicited. Three relatively normal PTH responses were obtained, two in an infant after phosphate-induced hypocalcemic tetany was corrected, and one in a child with a malabsorption syndrome. The renal tubular reabsorption of phosphate was inversely related and the urinary cyclic AMP excretion was positively related to the PTH response. Thus EDTA infusions in infants and children might be useful in the identification of hyper-, normo-, or hypoparathyroid states and would be of value in defining the functional condition of the parathyroid glands in children with deranged Ca or P metabolism.

Regulation of circulating parathyroid hormone levels: normal physiology and consequences in disorders of mineral metabolism

A review of the chemistry, the biosynthesis, the regulation of the secretion and the metabolism of parathyroid hormone (PTH) provides a background to problems related to the determination of immunoreactive PTH levels in the blood of normal subjects and of patients suffering from disorders of mineral metabolism. Immunoreactive PTH measurements have to be interpreted in the light of the immunoheterogeneity encountered and the occurrence of several circulating PTH species with different molecular weights and immunological properties.

The effect of calcium infusions on renal handling of amino acids in hypophosphatemic vitamin D resistant rickets

Amino acid clearances were studied in four patients with hypophosphatemic vitamin D resistant rickets. T,e clearances of the single amino acids in the patients did not differ from that of control individuals for all amino acids tested. The reabsorption of amino acids and phosphate was further investigated with the use of calcium infusions. Under these conditions there was a significant decrease in the filtered fraction of phosphate and amino acid excreted in the vitamin D resistant group suggesting a depression of parathyroid hormone secretion. It seems likely, as demonstrated in the vitamin D resistant group, that in this disorder the renal tubule is particularly sensitive to changes in parathyroid hormone secretion in respect to amino acid reabsorption.