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.

Diseases

Hypomagnesemia with hypercalciuria and nephrocalcinosis with ocular involvement
	Hypomagnesemia is a cardinal symptom of FHHNC with ocular involvement. Typical of this disorder is further hypocalcemia, due to excessive renal losses of divalent cations; nephrocalcinosis; recurrent kidney stones; progressive renal failure; and macular coloboma.
Gitelman syndrome
	Along with hypokalemia, hypomagnesemia is a cardinal symptom of Gitelman syndrome.
Intestinal hypomagnesemia with secondary hypocalcemia
	Hypomagnesemia is a cardinal symptom of HSH. Typical of this disorder is further hypocalcemia, wich is secondary and due to excessive renal losses.
Isolated dominant hypomagnesemia
	Hypomagnesemia is the single symptom of isolated hypomagnesemia (IDH). No other solute disturbances are seen.
Hypomagnesemia with hypercalciuria and nephrocalcinosis
	Hypomagnesemia is a cardinal symptom of FHHNC without ocular involvement. Typical of this disorder is further hypocalcemia, due to excessive renal losses of divalent cations; nephrocalcinosis; recurrent kidney stones; and progressive renal failure.
Hypomagnesemia with normocalciuria
	Hypomagnesemia 4 is characterized by normocalcemia and a normal range renal magnesium excretion in hypomagnesemia.
MODY5 diabetes
	Hypomagnesemia is observed in most of the patients with MODY5 though it is not a symptom that dominates the clinical picture.
Renal cysts and diabetes (RCAD)
	Hypomagnesemia is observed in most of the patients with RCAD though it is not a symptom that dominates the clinical picture.