Title: Calcium & Magnesium Deficiency

Key words: case history, calcium deficiency, magnesium deficiency, hypocalcaemia, hypomagnesaemia, alcoholism

Date: July 2000

Category: 3. Micronutrients

Type: Article

Author: Dr van Rhijn

 

 

Calcium & Magnesium Deficiency

A Case History Approach

A 52 year old male is admitted to hospital after being found collapsed. A history is obtained from relatives of high alcohol intake and recent profuse watery diarrhoea. He has a seizure and is found to have adjusted calcium of 1.95 mmol/L (RR 2.2 - 2.6). Despite three days of calcium infusion his adjusted calcium remains below 2.00 mmol/L in the presence of a PTH of 2.6 pmol/L (RR 1.1 6.9). The likely reasons for the abnormalities observed and an appropriate short/long term management plan are discussed below.

 

Assessment

The patient, now assumed to be stable and safe, should be further assessed by exploring other causes of hypocalcaemia, such as low albumin, chronic renal failure, acute pancreatitis (alcohol abuse), vitamin D deficiency and resistance to parathyroid hormone1. Tests should include serum urea, creatinine, amylase, lipase, albumin, Vit. D metabolites and parathyroid antibodies. Magnesium (Mg) depletion should almost by definition be considered in this case, as the most likely reason for a treatment resistant hypocalcaemia2 is low body Mg status, often under-diagnosed3 in 70% of patients4. The low plasma parathyroid hormone PTH and neurological signs support this theory. This is confirmed by a blood test of plasma Mg < 0,5 mmol/L, (normal range 0.7 1.1 mmol/L) and a low urinary output (mg < 2.0 mmol/day). Investigations are incomplete without considering causes of Mg depletion: drugs (diuretics, cisplatinum5) and illnesses: short gut syndrome (malabsorption), parathyroidectomy, pancreatitis, CVD, hypertension, IDDM, diabetic ketoacidosis, osteoporosis and CFS.

Possible Reasons for Clinical Abnormalities

Profuse watery diarrhoea can cause acute Mg deficiency where intake is inadequate (less than the RNI of 300mg/day). Alcohol abuse can cause chronic Mg deficiency through renal loss and a high carbohydrate diet. Calcium (Ca) deficiency usually develops with hypomagnesaemia and may cause tetany6.

 

Ca Mg Interdependency

Ca homeostasis is partly controlled by a Mg-requiring mechanism that releases parathyroid hormone and Ca inhibits a large number of Mg-activated enzymes. They have complex interdependent influences on the excitability of neurotransmitter activity. The factor that initiates hypocalcaemia appears to be a failure of the normal hererionic exchange of bone Ca for Mg at the labile bone-mineral surface, with impaired secretion and responsiveness (resistance) to parathyroid hormone (PTH) of the osteoclast receptor7. Inadequately low concentrations of PTH are a constant feature of hypomagnesaemic hypocalcaemia (HMHC), resulting in the failure of membrane-bound adenylate cyclase in the parathyroids, kidneys and bone8. Tetany induced by hypomagnesaemia in neonates is often characterised by hypocalcaemia resistant to calcium supplementation9.

These transient PTH resistance states10 are reversed with Mg supplementation11. Hypomagnesaemia in adults (60% of ICU patients) is characterised by salivation, nervousness, twitching, unsteady gait and tetany that may progress to convulsions and may be associated with delirium, hallucinations coma and death. Ca deficiency also causes paraesthesia, cramps, tetany and convulsions. Mg2+/Ca2+ ionic balance is required for normal neuromuscular transmission and Mg2+ is a natural Ca channel blocker.

Treatment

The main cause for low Mg levels should be treated and the Mg levels corrected.

Commence treatment with intramuscular injections of 5% magnesium sulphate (0.5 1.0 ml), repeated daily with a dose of (0.4 0.75 mmol/kg body weight) or parenteral infusion12 of 25 - 50 mmol MgCl in 1 liter of 5% dextrose or other isotonic fluid over 24 hours until full remission is achieved, usually in 3-7 days.

Daily magnesium supplementation of 300 600mg in divided doses. Provide good nutritional advice and enrol in an alcohol treatment plan.

Conclusion

Severe magnesium depletion leading to hypocalcaemia, described in a variety of clinical settings, is frequently under-diagnosed, justifying further education of clinicians in the significance of hypomagnesaemia.

 

References

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