What Is It, Causes, Symptoms, Treatment, and More
Author: Anna Hernández, MD
Editors: Ahaana Singh, Lisa Miklush, PhD, RN, CNS
Illustrator: Jillian Dunbar
What is tetany?
Tetany is a symptom characterized by the involuntary contraction of muscles that leads to painful muscle cramps, spasms of the voice box (i.e., larynx), and sensory disturbances. It is most commonly associated with low blood calcium levels, or hypocalcemia, although it can also appear with other metabolic irregularities.
What causes tetany?
Tetany is a classic sign of hypocalcemia, which refers to the presence of low calcium levels in the blood. Maintaining stable calcium levels is important for the adequate functioning of many cellular processes, such as neuronal activity, muscular contraction, hormone secretion, and blood coagulation. Blood calcium levels are regulated by the parathyroid hormone (PTH), which is released into the circulation when calcium levels are too low.
Hypocalcemia can result from a decreased level of PTH or, more rarely, increased resistance to its activity. This condition is known as hypoparathyroidism and can occur as a result of surgical removal of the parathyroid gland, autoimmune disorders or genetic conditions involving the parathyroid gland (e.g., DiGeorge’s syndrome), or magnesium deficiency.
Moreover, low levels of vitamin D can also lead to hypocalcemia. Vitamin D deficiency can result from a deficient diet, intestinal malabsorption, lack of sunlight exposure, or chronic kidney failure, among other causes. Finally, hypocalcemia can occur as a result of too much calcium leaving the blood, which can be seen in individuals with kidney failure, extensive burns, acute pancreatitis, severe infections, and treatment with several medications.
Aside from hypocalcemia, there are other metabolic irregularities that can also lead to tetany, including other electrolyte imbalances and disorders affecting the acid-base balance. Often, the cause of tetany involves a combination of metabolic abnormalities rather than a single cause.
Why does hypocalcemia cause tetany?
Calcium ions play an important role in stabilizing the resting membrane potential of neurons, thereby preventing their spontaneous activation. Hypocalcemia causes increased neuromuscular excitability by decreasing the threshold needed for the activation of neurons. As a result, neurons become unstable and fire spontaneous action potentials that trigger the involuntary contraction of the muscles, which eventually leads to tetany.
What are the symptoms of tetany?
Tetany can present with a variety of clinical manifestations, ranging from mild sensory disturbances to severe, life-threatening complications. Mild symptoms include numbness around the mouth, painful muscle cramps, and a burning or tingling sensation of the hands and feet, known as paresthesias. In severe cases, individuals may present with spasms of the voice box (i.e., laryngospasm), which can make breathing difficult and lead to high-pitched sounds while breathing (i.e., laryngeal stridor). Individuals with tetany may also experience vomiting, generalized muscle cramps, seizures, and decreased cardiac function, such as an irregular heart rhythm. Muscle cramps occur when a muscle contracts involuntarily and is not able to relax, leading to significant pain.
How is tetany diagnosed?
Tetany is often suspected in individuals with muscle cramps, paresthesias affecting the hands and feet, and numbness around the mouth. These symptoms can be recognized by assessing an individual’s sensory and motor functions in a thorough neurological examination. In some individuals, symptoms of tetany may not be as evident, and the diagnosis may require a high clinical suspicion. In some cases, other clinical signs, such as Trousseau’s sign, can be indicative of hypocalcemia-related tetany.A tetany diagnosis is usually confirmed by evidencing low calcium levels in the blood. In addition, blood levels of parathyroid hormone (PTH), vitamin D, magnesium, and phosphorus may help identify the underlying cause of tetany in an individual.
What is Trousseau’s sign?
Trousseau's sign refers to the muscle spasm of the wrist and forearm muscles that occurs after the occlusion, or blocking, of the brachial artery (i.e., the main blood vessels of the arm) with a blood pressure cuff. Trousseau’s sign is used to unmask latent tetany in people without evident symptoms of hypocalcemia.
How is tetany treated?
Severe tetany generally requires urgent intravenous (IV) calcium replacement. It is important to check magnesium levels during calcium repletion, as magnesium deficiency is a common cause of treatment-resistant hypocalcemia. For the correction of mild hypocalcemia, oral calcium supplements, vitamin D supplementation, or magnesium tablets may be required to restore calcium levels. Once the acute episode has been resolved, future management should focus on addressing the underlying cause of tetany.
What are the most important facts to know about tetany?
Tetany is a symptom characterized by the involuntary contraction of muscles that usually results from low calcium levels in the blood (i.e., hypocalcemia). Common symptoms of tetany include numbness around the mouth, muscle cramps, and paresthesias affecting the hands and feet. Severe symptoms include difficulty breathing due to muscle spasms of the voice box (i.e., laryngospasm), seizures, and decreased cardiac function. With observation of these symptoms, test results showing low calcium levels in the blood confirm a tetany diagnosis. The main goal of treatment is to normalize calcium levels using calcium supplements and, if appropriate, vitamin D and magnesium supplementation.
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Resources for research and reference
Hall, J. (2015). Guyton and Hall textbook of medical physiology (13th ed.). Philadelphia, PA: Elsevier.
Johnson, M., Patel, S., & Williams, J. (2019). Don't take it 'lytely': A case of acute tetany. Cureus, 11(10), e5845. DOI: 10.7759/cureus.5845
Patel, M., & Hu, E. (2020). Trousseau sign. In StatPearls. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK557832/Williams, A., Liddle, D., & Abraham, V. (2011). Tetany: A diagnostic dilemma. Journal Of Anaesthesiology, Clinical Pharmacology, 27(3), 393–394. DOI: 10.4103/0970-9185.83691