Introduction

You may have heard of electrolytes often discussed in connection with dehydration and, most commonly, in ads for sports drinks that replace the electrolytes lost through sweat. Nevertheless, what other purpose do they serve? Firstly, electrolytes are important for everyone, not only athletes or gym enthusiasts. This is because they perform a variety of functions in the body, such as secreting endocrine hormones, regulating membrane permeability, and controlling nerve and muscle function, among others. 

These electrolytes include: calcium, sodium, potassium, chloride, magnesium, copper, zinc, etc. However, an imbalance can occur whereby the levels of these electrolytes are either too high or too low. This can lead to the onset of various health conditions. One of these health problems is a condition called tetany, which can be caused by low magnesium levels (i.e. hypomagnesemia). This article reveals some concise information on the causes and mechanisms of hypomagnesemia-induced tetany.

Definition of hypomagnesemia and tetany

Hypomagnesemia is a condition that results when you have low levels of magnesium in the blood. The normal range of magnesium is between 1.6-2.6mg/dL. Thus, magnesium levels below 1.6mg/dL indicate hypomagnesemia.¹ Magnesium is involved in an array of functions in the body. These include: the transfer and storage of energy, the regulation of parathyroid hormone, the synthesis of DNA and protein, neuromuscular excitability, and numerous enzyme functions.² Thus, hypomagnesemia can induce adverse effects in almost every organ of the body, ranging from acute to chronic manifestations. 

Tetany is a group of symptoms associated with neuromuscular excitability. It occurs due to excessive stimulation of the peripheral nerves triggered by electrolyte imbalances in the body.³ Tetany occurs in two forms: manifest and latent. Manifest tetany is most commonly caused by hypocalcemia and presents with numbness and prickling sensations on the skin. There can also be paroxysmal contractions of the muscles of the face, feet, and hands.¹ Latent tetany occurs chiefly due to hypomagnesemia and is typically diagnosed based on diagnostic symptoms such as the Chvostek and Trousseau signs.¹ Hypokalemia, hyperventilation, and alkalosis are also responsible for the symptoms associated with tetany.⁴

Mechanism of hypomagnesemia-induced tetany 

Magnesium is an important mineral that plays diverse roles in various enzymatic processes in the body. These range from energy and protein metabolism to regulating cellular processes such as ion channels, production of parathyroid hormone, etc. Parathyroid hormone induces calcium release by the bones, assisting the kidneys in the reabsorption of calcium, and the synthesis of calcitriol (active Vitamin D). Thus, an imbalance in magnesium levels results in numerous clinical manifestations usually accompanied by hypocalcemia.⁵ Causes of hypomagnesemia include: certain medications, malabsorption, nutritional deficiencies, renal diseases, and endocrine disorders.⁵

Hypomagnesemia impairs the functioning of the parathyroid gland, which is responsible for the production of the parathyroid hormone.⁶ The parathyroid hormone increases calcium levels in the blood when it is too low. Therefore, when magnesium levels are too low, insufficient parathyroid hormone is produced, resulting in low calcium levels in the blood. Hypomagnesemia and hypocalcemia cause a plethora of neurological symptoms that can begin in infancy, which include involuntary muscle spasms (i.e. tetany), tremors, fasciculation, convulsions, apathy, delirium, and seizures.¹ Other life-threatening complications that can occur due to a combination of hypomagnesemia, hypocalcemia, and hypokalemia include ventricular arrhythmia, torsades de pointe, and in severe cases, sudden death.⁷ Additionally, long-term complications include hypertension, atherosclerosis, osteoporosis, asthma, and irreversible organ damage.⁷ 

What causes hypomagnesemia-induced tetany? 

Generally, an electrolyte imbalance causes the onset of tetany. However, hypomagnesemia induces tetany because magnesium influences the metabolism of calcium and potassium. Low levels of magnesium in the cerebrospinal fluid (CSF) can facilitate calcium-dependent neurotransmitter release and uncontrolled excitability of the neurons in the central nervous system.¹¹ Consequently, this causes the onset of the clinical signs associated with tetany. Calcium plays a crucial role in neuromuscular excitability, coagulation, and bone mineralisation.⁸ Hypocalcemia is caused by low levels of parathyroid hormone, vitamin D deficiency, and increased levels of calcitonin.⁸ 

Potassium supports muscle and nerve function, including the regulation of heart rate and muscle contractions. Hypokalemia occurs due to low levels of potassium in the blood (i.e. < 3.5 mEq/L) and usually occurs with hypomagnesemia. Also, the repletion of potassium, which is often linked to magnesium depletion, is resolved only after the magnesium deficiency has been normalised.⁹ In other words, hypomagnesemia, which is usually accompanied by hypocalcemia and hypokalemia, induces the hyper-excitability of the neurons, which in turn, triggers the onset of tetany. In sporadic cases, tetany may be caused by genetic disorders, such as Gitelman syndrome or Bartter’s syndrome. These are associated with loss of electrolytes in the urine.¹²

Clinical features and symptoms of hypomagnesemia-induced tetany

Magnesium is the 2nd most abundant mineral in the body. The percentage of magnesium is 60% and 40% in the bone and soft tissues, respectively.¹⁰ Magnesium influences the levels of other vital electrolytes, therefore, an alteration in the concentration of magnesium induces neuromuscular manifestations, which include tetany.¹⁰ Thus, the clinical features of hypomagnesemia-induced tetany are as follows:

• Tachycardia
• Double vision 
• Spasms of the eyelid
• Coronary and abdominal vasospasm
• Raynaud’s Phenomenon¹²

The symptoms of latent tetany (which occurs due to hypomagnesemia) can be subdivided into nervous system symptoms and manifestations in the body's organs. These include; 

Treatment of hypomagnesemia-induced tetany

Effective treatment of hypomagnesemia-induced tetany involves identifying the specific cause of the condition. Thus, diagnosis and treatment are tailored according to electrolyte disturbances in the individual. Suppose test results indicate a calcium, magnesium, or other electrolyte deficiency. In this case, the treatment might include supplementing these electrolytes or making major dietary changes.¹² However, the resolution of hypomagnesemia is paramount as it is the underlying trigger of other electrolyte imbalances.¹²  

The treatment of hypomagnesemia-induced tetany involves supplementation with magnesium and Vitamin B6.¹² For patients exhibiting psychotic symptoms of hypomagnesemia-induced tetany, such as delirium, hallucination, and mood disorders, psychotherapy, relaxation techniques, and use of selective serotonin reuptake inhibitors (SSRIs) can be considered.¹² 

Prevention of hypomagnesemia-induced tetany

Individuals who have undergone thyroidectomy or those who use drugs that affect electrolyte levels, such as proton-pump inhibitors or loop diuretics, should be strongly advised to undergo tetany prophylaxis. This involves testing for electrolyte levels and appropriate supplementation with magnesium, calcium, or potassium. ¹² However, it is imperative to monitor and adjust the dosage of these supplements to individual needs to prevent relapse or other complications due to overdose. 

Diagnosis of hypomagnesemia-induced tetany

The diagnosis of tetany depends on the presence of typical clinical symptoms, laboratory tests, electromyography (EMG), electroencephalography (EEG), electrocardiography (ECG), and low magnesium levels in the blood or cerebrospinal fluid.¹³ If there is suspected latent tetany, the following diagnostic tests are recommended; 

• Chvostek sign: This involves the involuntary twitching of the innervated muscles following tapping of the facial nerves, which are anterior to the external auditory meatus
• Trousseau sign: This is a clinical indicator of increased neuromuscular irritability, evidenced by the onset of carpal spasm. In this test, the hand adopts a characteristic posture (known as obstetrician’s hand) when the sphygmomanometer cuff is inflated above the systolic blood pressure within 3 minutes
• Lust sign: This is the contraction of the group of muscles in the lower leg, followed by abduction of the foot in response to tapping of the peroneal nerve
• Erb’s sign:  This is one of the most reliable clinical signs of tetany. It is based on the neuromuscular response to electrical stimuli. It is characterised by increased excitability of the motor nerve in response to galvanic current¹²
• Maslow sign: This is characterised by an increased rate of breathing as a result of pricking with a pin¹²

Summary 

Tetany is a condition caused by the imbalance of various electrolytes, and hence, it presents with a variety of symptoms. Hypomagnesemia-induced tetany is usually triggered by a certain stimulus (such as magnesium deficiency, hyperventilation, etc) before the manifestation of symptoms. Contrarily, manifest tetany presents with obvious symptoms such as spasm of the eyelids, numbness and paresthesia in the fingertips. Treatment of hypomagnesemia-induced tetany includes adequate supplementation with magnesium, calcium, potassium and Vitamin D. The main hallmark diagnostic tests for tetany are Chvostek and Trousseau signs. Also, tetany prophylaxis is recommended for individuals with electrolyte imbalance, who use certain medications and have undergone certain surgical procedures. Hypomagnesemia-induced tetany highlights the importance of detecting and resolving electrolyte abnormalities, which can elicit severe complications that involve the cardiovascular system.

FAQs

Do tetany and tetanus mean the same thing?

No, although these two conditions sound similar, they shouldn’t be confused or used interchangeably. Tetany is basically a symptom caused by the imbalance of electrolytes in the body; hypomagnesemia, hypocalcemia and hypokalemia. Tetanus is an infectious disease caused by the bacterium Clostridium tetani, which releases a neurotoxin that affects the central nervous system. 

How do you know if you have hypomagnesemia-induced tetany?

Apart from the onset of neurological symptoms, various biochemical tests are used to evaluate the total concentration of calcium, magnesium, potassium and parathyroid hormone levels. However, the most sensitive test for detecting neuromuscular excitability is electromyographic examination (EMG), also known as the tetany test. 

Can hypomagnesemia-induced tetany be inherited? 

Although tetany can be caused by a genetic disorder, there is evidence of low heritability of this condition. Thus, it is rarely inherited.