Definition and pathophysiology of tetany

Tetany is induced by alterations in the body’s electrolyte levels, causing involuntary muscle contractions, cramping or spasms and hyperexcitability of the peripheral nerves.¹

Electrolytes are minerals which are crucial for bodily functions as they maintain the fluid balance and electrical neutrality of cells, as well as help to generate action potentials for signalling and chemical reactions. There are several important electrolytes, namely sodium, potassium, chloride, magnesium, calcium, phosphate, and bicarbonates, and they are obtained via food and fluids.^2,3 When variations are causing the electrolyte levels to either be high or low, the body’s homeostasis is disrupted, leading to complications such as cardiac arrhythmias, diarrhoea, vomiting and tetany depending on which electrolyte is affected.²  

Causes

Hypocalcemia 

The most common cause of tetany is hypocalcemia, which is when the levels of bodily calcium are too low. Calcium is necessary for good bone and teeth health, blood clotting, muscle contraction, nerve impulse transmission, and the secretion of hormones.² Along with muscle-specific issues like spasms and loss of control, hypocalcemia can also cause confusion and behavioural changes.³ Low calcium levels are often due to hypoparathyroidism (low levels of parathyroid hormone) and a deficiency in vitamin D.¹ 

Hypomagnesemia

Magnesium allows adenosine triphosphate (ATP) metabolism so that cells can store and use energy. It is also required for muscle function, the release of neurotransmitters and neurological functioning. Overuse of alcohol and kidney issues contribute to low magnesium levels, which then present with heart arrhythmias and muscle problems.^2,3 

Hypokalemia

As potassium is important for normal nerve and muscle cell function, especially in the heart, symptoms include fatigue, muscle weakness, twitching and cramps as well as feeling thirsty and having the urge to pee frequently. The use of diuretics, vomiting, diarrhoea and chronic kidney disease can bring about hypokalemia.^1,2,3

Metabolic alkalosis

Alkalosis is defined as the buildup of excess base or alkali in the body, increasing the blood’s pH and can be due to metabolic or respiratory causes. In metabolic alkalosis, there’s an excess loss of hydrogen ions, increased bicarbonate in the body’s fluids and/or increased absorption of bicarbonate in the kidneys.^1,4

Respiratory alkalosis

Respiratory alkalosis is usually induced by hyperventilation - breathing rapidly or too deeply. This causes a loss of excess carbon dioxide, decreasing the blood’s levels, so it is now alkaline. Notably, a common physiologic cause of hyperventilation is pregnancy due to increased metabolic rates.^1,4

Clinical presentation

The signs of tetany are listed based on severity below: ^1,5

Mild signs

• Muscle cramps
• Muscle spasms 
• Numbness around the mouth
• Paresthesia (a tingling, numbness or burning feeling) of hands and feet

Severe signs

• Laryngospasm (spasm of the vocal cords)
• Bronchospasm (spasm of the muscles that line the lungs’ airways)
• Seizures
• Generalised, painful muscle cramps
• Myocardial dysfunction
• Vomiting 

Rhabdomyolysis, although rare, can occur as a result of severe tetany cases where the muscles break down and die. This condition can be life-threatening.¹

Challenges in diagnosing tetany in pregnancy

Overlapping symptoms with other conditions 

Unfortunately, tetany can be difficult to diagnose during pregnancy as its symptoms often overlap with other common obstetric conditions like:

• Eclampsia – this condition normally presents with seizures and is a severe form of preeclampsia, a pregnancy complication characterised by high blood pressure⁵
• Neurological disorders – epilepsy or peripheral neuropathy, present with muscle weakness, twitching, as well as paresthesia of hands and feet^6,7

Subtle or atypical presentations

The signs of tetany can be vague, so they can be overlooked:⁸

• Carpopedal spasms – these are involuntary muscle contractions that may be mistaken for normal muscle cramps or fatigue in pregnancy
• Paresthesia – tingling or numbness in the limbs is another sign that can be linked to pregnancy

Management strategies

Tetany can be managed through several avenues:^1,9

1. Correcting calcium levels with intravenous calcium replacement or oral elemental calcium
2. Addressing underlying conditions like thyroid/parathyroid dysfunction
3. Addressing associated deficiencies, electrolyte imbalances or alkalosis, e.g. with vitamin D supplements, magnesium tablets or oxygen supplementation

Complications 

Maternal and fetal risks

Complications occur from under- or overtreatment in pregnant or nursing women with hypocalcemia. Under treatment in maternal hypocalcemia caused by hypoparathyroidism is associated with intrauterine fetal hyperparathyroidism and fetal death. On the other hand, overtreatment leads to maternal hypercalcemia, which can cause complications such as abortion, stillbirth, perinatal death, neonatal tetany, and suppression of the parathyroid glands of the fetus and newborn.⁸

FAQs

How is tetany treated in pregnancy?

The treatment of tetany in pregnancy includes: 

• Intravenous calcium gluconate or calcium chloride
• Calcium supplementation
• Dietary intake of calcium-rich foods
• Supplementation with vitamin D3 to improve calcium absorption
• Magnesium sulfate (if hypomagnesemia is present)
• Foods rich in magnesium 
• Oxygen supplementation in cases of respiratory compromise
• Intubation and ventilation if tetany leads to respiratory arrest or severe laryngeal spasm
• Potassium chloride supplementation
• Focus on nutrient-dense foods and avoid substances that hinder calcium absorption, such as high caffeine or sodium intake

What will happen if a pregnant woman suffers from calcium deficiency?

1. Muscle and neuromuscular symptoms – tetany, paresthesia, osteopenia and osteoporosis
2. Increased risk of hypertension and preeclampsia 
3. Fatigue and weakness
4. Poor bone development in the baby 
5. Intrauterine growth restriction (IUGR)
6. Preterm birth and low birth weight
7. Neonatal hypocalcemia
8. Potential long-term effects

What happens if a pregnant woman has too much calcium?

• Gastrointestinal symptoms – nausea, vomiting, and constipation 
• Kidney problems – kidney stones, reduced kidney function
• Neurological symptoms – confusion, lethargy, or, in severe cases, coma 
• Cardiac issues – arrhythmias 
• Suppressed parathyroid gland activity in the fetus leads to neonatal hypocalcemia (low calcium levels), which can cause tetany or seizures.
• Skeletal abnormalities in babies
• Preterm labour and birth
• Fetal growth restriction

Summary

Tetany in pregnancy is considered to be a symptom caused by variations in the electrolyte levels, which in turn cause muscle contractions, spasms, and hyperexcitability of nerves. The most associated electrolyte is calcium, and as a result, hypocalcemia (low calcium blood levels) is often the cause of tetany, However, low magnesium (hypomagnesemia) and low potassium (hypokalemia) can also play a part, as well as metabolic and respiratory alkalosis, such as those caused by hyperventilation during pregnancy

The signs of tetany can range from mild (muscle cramps, numbness, tingling of extremities) to severe (laryngospasm, seizures, cardiac dysfunction). Diagnosing tetany during pregnancy can be quite challenging due to the similar symptoms with medical conditions like eclampsia and neurological disorders, as well as the atypical nature of these symptoms/signs. 

Management includes correcting electrolyte imbalances with treatments like calcium supplements, magnesium, and addressing underlying conditions. Risks from improper treatment include complications like fetal death from under-treatment or neonatal tetany from over-treatment.

Appropriate management strategies focus on maintaining balanced calcium, magnesium, and potassium levels and avoiding factors that hinder nutrient absorption, such as excessive caffeine intake.