Hypomagnesemia in Cats
Hypomagnesium is a clinical disorder in which the body is suffering from a deficiency in magnesium. Magnesium is second only to potassium as the most abundant substance in the cells. Most is found in the bone (60 percent) and soft tissue (38 percent), and most of the soft tissue magnesium resides in the skeletal muscle and liver. Magnesium is required for many metabolic functions, it is an activator or catalyst for more than 300 enzyme systems, including enzymes that involve adenose triphosphat (ATP), which transports chemical energy within the cells for metabolism.
Magnesium is an important cofactor in maintaining an electrical balance across membranes, and is also important in the production and elimination of acetylcholine (a neurotransmitter); a low concentration of magnesium in the extracellular fluid (fluid outside of the cells) can increase concentrations of acetylcholine at motor endplates, resulting in an involuntary reaction of muscles. Interference with the electrical gradient can result in neuromuscular and cardiac abnormalities.
Some of the complications that can occur with hypomagnesemia are alterations of the functions of the skeletal muscles, resulting in tetany (severe muscular pain) and a variety of myopathies (diseases of skeletal muscles); ventricular heart arrhythmias, or torsades de pointes (a tachycardia, or fast heart rhythm that originates in one of the ventricles of the heart), and depolarization of cardiac cells and tachyarrhythmias (fast heart rhythms); resistance to the effects of parathyroid syndrome; an increase in the uptake of calcium into bone; and an increase in the risk of digoxin (digitalis) toxicity.
- Muscle trembling
- Ataxia (muscle incoordination)
- Hyperreflexia (overactive reflexes)
- Tetany (severe muscle pain)
- Behavioral changes
- Arrhythmias (abnormal heart rhythms)
- Severe malnutrition or significant malabsorptive intestinal diseases
- Nephrotoxic drugs (drugs that are poisonous to the kidneys)
- Diabetes mellitus
- Use of diuretics (drugs to rid the body of excess fluid)
- Excessive calcium excretion through urination
- Decreased intake of magnesium, may occur due to lack of magnesium in parenteral (intravenous or injected) fluids in patients receiving long-term fluid therapy or dialysis
Because there are several possible causes for this condition, your veterinarian will most likely use differential diagnosis. This process is guided by deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately. Signs of hypomagnesemia are typically vague and affect one or more body systems. Therefore, other causes of neuromuscular abnormalities, and especially other electrolyte abnormalities, must be investigated. During the physical examination, your doctor will be looking for cardiac abnormalities, intoxications related to drugs/medications, and kidney diseases, any of which can lead to some of the symptoms described above.
An electrocardiogram (ECG, or EKG) recording can be used to examine the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat), a common side effect of hypomagnesemia.
Treatment depends on the underlying cause of the abnormality and the severity of the hypomagnesemia. Because severe hypomagnesemia can be fatal, prompt and appropriate treatment is essential. Mild hypomagnesemia may resolve with treatment of the underlying disorder; however, if hypomagnesemia is severe, intensive care will be needed.
If digoxin is being prescribed, its use will have to be discontinued, if possible, until the hypomagnesemia has been resolved, and diuretics will need to be used with caution, or another form of fluid removal prescribed. In addition, it must be kept in mind that hpermagnesemia – too much magnesium in the body – is possible with overzealous treatment.
Living and Management
Initially, your veterinarian will want to check your cat's magnesium and calcium concentrations on a daily basis. During magnesium infusions, your doctor will also want to administer an ECG continuously to make sure that your cat's heart is staying within its normal rhythm.