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Case Reports Indian Pediatrics 2002; 39:296-299 |
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Primary Hypomagnesemia with Secondary Hypocalcemia in an Infant |
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Surabhi Agrawal Meena P. Desai
The association of hypomagnesemia with hypocalcemia is known for the past few years and in majority of these instances, disturbances of magnesium (Mg) homeostasis is secondary to an obvious cause. Primary hypomagnesemia due to disorder of magne-sium metabolism(1,2) though rare, has been reported. In these infants who are both hypomagnesemic and hypocalcemic, symp-toms and biochemical disturbances respond only to administration of magnesium salts. Hypomagnesemia is now reported in neonates and during early infancy(3-5) as a result of specific malabsorption of magnesium. Previously, only male infants were reported to be affected but now there have been a few documented cases in females. Here, we report one such infant who was followed up from the age of 6 weeks to 7 years. Case Report A breast-fed male infant, seventh issue born of a consanguineous marriage, was delivered normally at full term with a normal birth weight. He was referred at the age of six weeks for repeated attacks of generalized tonic and clonic spasms of two weeks duration, refusal of feeds and drowsiness for one week. The antenatal history was normal. A lumbar puncture done outside was reported to be normal. Use of parenteral pheno-barbitone and parenteral calcium therapy during this period produced only partial relief. The eldest female sibling, eleven years old was normal, but four elder female siblings had died of intractable convulsions between the age of six weeks to six months and a sixth male infant was still-born. In view of several siblings being affected, a metabolic disorder was suspected. On clinical examination, the infant weighed 4 Kg and was drowsy with no significant neurologic or physical findings. The serum calcium was low [5.2 mg/dl (N - 2 to 11 mg/dl) phosphorus was slightly elevated - 6 mg/dl (N - 4.5 to 5.5 mg/dl), with a normal alkaline phosphatase - 500 U/L (N - 145 to 420 Units/L)]. Complete blood count, urine and stool examinations were normal. X-ray chest and X-ray of bones were normal. Serum electrolytes, blood sugar, urea, creatinine, proteins, blood gases, serum ammonia, blood pyruvate and lactate were all within normal range. Urinary amino acids were also normal. EEG showed non-specific generalized abnormalities. Parenteral phenobarbitone(5 mg/kg/day in two divided doses) and parenteral calcium gluconate 10% (5 ml/kg/day in three divided doses) were given. This produced minimal clinical response and the serum calcium remained low. Serum magnesium estimated 24-hours later was low 0.9 mg/dl (N - 1.7 to 2.6 mg/dl). Parathyroid hormone value was normal 11 pg/ml (N - 9 to 65 pg/ml) by chemiluminescence method. Initiation of intra-muscular magnesium sulphate therapy (50% solution, 0.2 ml/kg/dose 8 hourly) produced dramatic clinical response with abolition of spasms and drowsiness with simultaneous increase in both serum magnesium and calcium levels. Thus a rise in serum calcium could be documented for the first time in 48-hours after the administra- tion of magnesium (Calcium 8.4 mg/dl, Magnesium 2.3 mg/dl). Magnesium sulphate therapy was continued during his stay in the hospital. At the time of discharge, ten days later, the patient was active, feeding normally and appeared neurologically normal. Patient was discharged on parenteral magnesium sulphate therapy initially daily and then on alternate days. On regular follow up till seven months of age, child was asymptomatic. Serum calcium levels remained normal, ranging from 8.2 mg/dl to 10.4 mg/dl and serum magnesium levels ranged from 0.8 mg/dl to 1.3 mg/dl. At the age of one year, patient was brought back with carpopedal spasms following inadvertent omission of magnesium therapy for a period of three weeks. On admission serum calcium was low 7.2 mg/dl with a low serum magnesium level of 0.6 mg/dl. Repeat values for serum phosphorus and serum parathyroid hormone were normal. Other biochemical investigations were within normal range. Renal profile and sonography for kidneys were normal and fat malabsorption studies were normal. Round the clock treatment with parenteral magnesium sulphate (50% solution, 0.2 ml/kg/dose 8 hourly) increased both serum calcium and serum magnesium levels to 10.4 mg/dl and 1.8 mg/dl, respectively. Meanwhile with great difficulty, magne-sium glycerophosphate was procured for oral administration. The patient was advised to give 3 g/day in three divided doses and discharged. The patient had to be readmitted three weeks later for recurrence of carpopedal spasms, as mistakenly, the infant was administered only 1 g/day of magnesium glycerophosphate, which resulted in hypo-calcemia and hypomagnesemia. Parenteral administration of magnesium sulphate alone produced adequate clinical as well as bio-chemical improvement. The serum calcium and serum magnesium levels increased to 9 mg/dl and 1 mg/dl, respectively. Serum magnesium level of 1 mg/dl seemed sufficient to bring about symptomatic relief as long as serum calcium levels could be maintained within normal range. Subsequently, the patient did not have any further episodes with continued treatment with magnesium glycerophosphate. He has been followed up till the age of seven years and has grown normally with normal neurological development. Discussion Deficiency of magnesium can lead to convulsive disorder with permanent neuro-logic impairment(6). In adults, chronic magnesium depletion has been linked with hypertension, arrythmias, atherosclerotic vascular disease, metabolic bone disease, renal stones and sometimes sudden death. Symptomatic hypomagnesemia is infrequent-ly encountered in children where it may be secondary to chronic diarrhea, protein energy malnutrition, hypo-parathyroidism, primary aldosteronism, renal tubular acidosis, hyper-calcemic states and a result of drugs like loop diuretics, aminoglycosides, cephalo-sporins, post intestinal resection(7) or long term treatment with intravenous fluids. In the neonates, transient hypomagnesemia is known to occur in babies of toxemic and diabetic mothers or in IUGR babies or with transient hypoparathyroidism or maternal hypomagnesemia due to celiac disease. None of these conditions could account for the disturbances of magnesium and calcium metabolism in this patient. Primary hypomagnesemia with secondary hypocalcemia is a rare genetic disorder(8) characterized by recurrent tetany(9) or convulsions in early infancy, or both, which are refractory to calcium supplementation but respond to magnesium treatment. In cases reported in literature, manifestations of primary hypomagnesemia were seen in early infancy ranging from the fifteenth day of life till the fourth month. It was initially believed that primary hypomagnesemia had X-linked recessive inheritance as it was reported only in male siblings(10). In view of the disorder being reported in female siblings in the last few years, autosomal recessive inheritance is now considered(11-14). Our patient had four elder female siblings who had died of intractable convulsions between the ages of six weeks to six months also suggesting autosomal recessive inheritance. This patient had significant hypocalcemia with hypomagnesemia. It was of interest to note that therapy with calcium as well as with magnesium alone resulted in clinical and caused elevation of serum calcium, which did not rise when only calcium was administered. Magnesium is the second most common cation in the body. Probably, till the tissue stores are depleted the clinical symptoms do not become manifest, hence the unpredictable relationship between spasms and the serum levels. Though magnesium metabolic balance studies and radioactive magnesium absorption studies could not be carried out in this patient, family history and rest of the investigations, follow up studies and the dramatic therapeutic response to magnesium therapy excluded other causes. Contributors: MPD co-ordinated the case study and helped draft the paper. She will act as guarantor for the paper. SA participated in the data collection and drafted the paper. Funding: None. Competing interests: None stated.
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