Hypermagnesemia – causes, symptoms, diagnosis, treatment, pathology

Hypermagnesemia – causes, symptoms, diagnosis, treatment, pathology


Learning medicine is hard work! Osmosis makes it easy. It takes your lectures and notes to create
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much more. Try it free today! ‘Hyper-’ means ‘over’ and ‘-magnes-’
refers to magnesium, and -emia refers to the blood, so hypermagnesemia means higher than
normal magnesium levels in the blood, and symptoms typically develop at a level over
4 mEq/L. An average adult has about 25 grams of magnesium
in their body. About half is stored in the bones, and most
of the other half is found within cells. In fact, magnesium is a really common positively
charged ion found within the cell, second only to king potassium. A very tiny fraction, roughly 1% of the total
magnesium in the body, is in the extracellular space which includes both the intravascular
space – the blood and lymphatic vessels, and the interstitial space – the space between
cells. About 20% of the magnesium in the extracellular
space, which would be about 0.2% of the total magnesium, is bound to negatively charged
proteins like albumin, but the other 80% or 0.8% of the total magnesium, can be filtered
into the kidneys. So in the kidney, that magnesium gets filtered
into the nephron, andi about 30% gets reabsorbed at the proximal convoluted tubule, 60% gets
reabsorbed in the ascending loop of Henle, and 5% get reabsorbed at the distal convoluted
tubule. That leaves only 5% to get excreted by the
kidneys. So, in order for there to be too much magnesium
in the blood, this normal balance has to be disturbed. The most common reason is when those nephrons
in the kidneys can’t excrete magnesium properly – which can happen in renal failure, when
the kidneys typically aren’t able to excrete anything properly. Another cause of hypermagnesemia is ingesting
more magnesium than the kidneys can excrete. Sometimes this can be due to an intravenous
infusion of magnesium that isn’t prepared correctly. Other times it can be due to a magnesium containing
medication like magnesium hydroxide which can be used to treat symptoms like constipation
and heartburn. If these medications are taken in excess over
a long period of time, it can lead to hypermagnesemia.There are some less common causes of hypermagnesemia. One of these is tumor lysis syndrome which
results from a rapid number of cancer cells dying in unison releasing their contents – which
includes magnesium. Hypermagnesemia can cause some serious complications. At the neuromuscular junction, there are voltage-gated
calcium channels on presynaptic neurons which need to open and let calcium in to cause the
neuron to release neurotransmitter and cause muscle contraction. Under normal circumstances, magnesium seems
to inhibit calcium influx a little bit, which actually helps stabilize the axon. But with too much magnesium floating around,
it tends to inhibit calcium influx even more, which interferes with neurotransmitter release
and ultimately slows muscle contraction. Also, normally the parathyroid hormone from
the parathyroid gland usually stimulates calcium release into the blood. High levels of magnesium in the blood seems
to inhibit release of parathyroid hormone from the parathyroid gland, which causes calcium
levels to fall, leading to hypocalcemia. Typically the resulting hypocalcemia is transient
and asymptomatic. Really high levels of magnesium also alter
the electrical potential across the cardiac cell membrane, which can lead to cardiac arrhythmias
like heart block and even asystole. Anytime hypermagnesemia is causing symptoms,
the level of free magnesium ions in the blood is usually over 4 meq/L. Treatment depends
on the cause, and if its due to excessive intake, then interrupting the source cures
the condition. Because calcium and magnesium compete for
binding, some of the symptoms of hypermagnesemia can be countered by injecting calcium, usually
in the form of calcium gluconate, which acts as a physiological antagonist. Sometimes furosemide can be used to promote
kidney excretion of magnesium, and hemodialysis can also be used in severe cases. Alright, as a quick recap – Hypermagnesemia
refers to an elevated free magnesium ion level which usually causes symptoms once its over
4 meq/L. This can be caused by impaired excretion by the kidneys or an increased intake of magnesium. The magnesium antagonizes calcium and can
lead to a neuromuscular blockade causing symptoms like vasodilation, muscle weakness, and even
cardiac arrhythmias.

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