Hypomagnesaemia
Hypomagnesaemia is plasma magnesium concentration below the normal range.
Clinical Findings
Cardiovascular symptoms of hypomagnesaemia include atrial and ventricular arrhythmias, hypertension, coronary artery spasm, and sudden death due to one of these pathologies. Various rather unspecific neuromuscular symptoms have been associated. These include weakness, muscle fasciculations, tremors and tetany, and positive Chvostek's and Trousseau's signs.
Following long standing hypomagnesaemia, refractory hypocalcaemia and hypokalaemia may develop.
Diagnosis
Hypomagnesaemia is easy to measure, but difficult to interpret. Medical history may reveal underlying gastrointestinal or renal diseases, toxic effects especially those due to medication, and possibly, clues for inheritance. Laboratory tests include measurement of all solutes in plasma and urine. It is helpful to determine renal excretion by calculation fractional clearance of all electrolytes. Lab is completed by measuring arterial blood gases and hormones related to electrolyte disorders, mostly renin and aldosterone.
Pathogenesis
Although magnesium stores in bone account for 99% of total body magnesium, these stores are only slowly released. Therefore short-term requirements in magnesium homeostasis are met by gastrointestinal absorption and renal excretion.
Conclusively, disturbed magnesium homeostasis is most often caused by gastrointestinal diseases with malabsorption, but renal magnesium wastage is also common.
Classification
We distinguish secondary and primary forms of hypomagnesaemia.
Physiology
The normal serum concentration of magnesium is 0.75-1.00 mmol/l (1.7-2.3 mg/dl). Magnesium in serum is either ionised (60-70%), or complexed (10%), or protein bound (20-30%). The daily intake of approximately 300-360mg or 12-14mmol is often considered at low limit for maintaining balance. Therefore in many cases magnesium supplementation does no harm and is rather of some benefit.
