Essay Example on Discussion Hypocalcemia is a potentially life threatening electrolyte Derangement









Discussion Hypocalcemia is a potentially life threatening electrolyte derangement Of most concern are cardiac sequelae such as prolonged QT interval cardiomyopathy and congestive heart failure 1 Hypocalcemia can also cause seizures so hypocalcemia must be ruled out in any child with unexplained seizure2 Other neurologic neuromuscular complications include paresthesias tetany muscle cramps and muscle weakness 1 2 Skin and bone growth are affected with risk increased for dental caries atopy psoriasis delayed tooth eruption delayed growth and osteoporosis 1 Other complications may include smooth muscle dysfunction and psychological abnormalities including confusion irritability fatigue difficulty concentrating and poor memory 1 Physical exam findings on a child with hypocalcemia may include facial muscle irritability Chvostek sign elicited by tapping on the maxilla or carpopedal spasm Trousseau sign which can be seen by inflating a sphygmomanometer to 20 mmHg above the systolic blood pressure for 3 5 minutes1 2 

In the acute setting causes of hypocalcemia include sepsis rhabdomyolysis pancreatitis tumor lysis syndrome or blood transfusions3 For a child who presents in the non acute setting with hypocalcemia the differential diagnosis can be restricted to chronic causes of hypocalcemia These include hypocalcemia with high parathyroid hormone PTH and hypocalcemia with low PTH PTH is a hormone that enhances bone resorption promotes the conversion of 25 hydroxyvitamin D to 1 25 dihydroxyvitamin D and increases intestinal and renal calcium absorption and phosphate renal excretion4 The most common cause of hypocalcemia with high PTH is hypovitaminosis D rickets 4 Other causes include disorders of vitamin D synthesis renal dysfunction PHP and hypomagnesemia4 Causes of hypocalcemia with low PTH also called hypoparathyroidism include congenital absence of the parathyroid glands genetic defects in the calcium sensing receptor or genetic defects in production or processing of PTH5 Autoimmune diseases and destruction or infiltrative disorders of the parathyroids can also cause hypoparthryoidism5 Distinguishing between these causes of chronic hypocalcemia can be difficult without genetic testing but the differential can be narrowed by performing a few key laboratory tests with hallmark values suggesting a diagnosis

Table 2 These tests include intact parathyroid hormone 25 hydroxyvitamin D and 1 25 hydroxyvitamin D Based on our patient s laboratory workup revealing hypocalcemia with elevated PTH elevated phosphate and normal 1 25 hydroxyvitamin D and 25 hydroxyvitamin D levels she was given the diagnosis of pseudohypoparathyroidism Described first in 1942 by Albright et al pseudohypoparathyroidism PHP is a rare constellation of genetic diseases that involve dysfunction of the GNAS gene on chromosome 20q13 6 7 This gene encodes the alpha subunit of the stimulatory G protein Gs α attached to the PTH receptor Dysfunction of this gene prevents the cell signaling cascade that stimulates the kidney to reabsorb calcium and excrete phosphate In the absence of this signaling calcium levels remain low while PTH and phosphate levels are high PHP is inherited in an autosomal dominant manner with an imprinting pattern the paternal allele is always silenced Thus PHP is always inherited from the mother7 PHP Type 1 is divided into three subtypes 1a 1b and 1c7 8 PHP Types 1a and 1c present with stereotyped physical features and other endocrine abnormalities collectively known as Albright's hereditary osteodystrophy AHO 8 Patients with AHO have short stature hypothyroidism hypogonadism and mental retardation as well as ovulatory gustatory and auditory dysfunction They may also have round faces shortening of the metacarpals obesity and subcutaneous calcifications7 However if the mutation is passed down from the father that allele is silenced and the biochemical and mineral abnormalities seen in PHP Type 1A are not seen i e these patients will not be hypocalcemic 

They will display only the features of AHO which is called pseudo pseudohypoparathyroidism9 PHP Type 1b is most often sporadic with unknown mutations but may involve loss of methylation or microdeletions of the GNAS gene 7 8 9 It often does not present with any AHO features but instead presents as isolated hypocalcemia with high PTH and high phosphate7 8 This form may be discovered incidentally later in life as patients may remain asymptomatic for years and have no overt physical abnormalities PHP Type 2 is rarely seen and the molecular defect responsible for this variant is unknown Because calcium and vitamin D replacement corrects the kidney's response to PTH in these patients it is hypothesized that this type of PHP may be not be a genetic defect and is instead acquired in the setting of vitamin D deficiency 7 10 11 Regardless of the type of PHP children with PHP must receive treatment with calcitriol with supplemental calcium and Vitamin D throughout life to enhance calcium absorption and prevent serious complications Children with PHP should also be assessed and treated for other endocrine disorders known to manifest with PHP including hypothyroidism hypogonadism and growth hormone deficiency 12 13 14 Genetic counseling later in life may be appropriate

Conclusion Pseudohypoparathyroidism PHP is a rare maternally inherited genetic disease that causes chronic hypocalcemia with high parathyroid hormone high phosphate levels and normal vitamin D levels This disease may present incidentally as refractory hypocalcemia in a child with no overt physical manifestations of disease It is an important diagnosis to recognize and treat as persistent hypocalcemia can be life threatening and detrimental to bone growth and health Treatment for this disease includes lifelong calcitriol with calcium and additional vitamin D supplementation Children who are suspected to have PHP should be screened and treated for comorbid endocrine disorders such as hypothyroidism hypogonadism and growth hormone deficiency

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