Hypocalcemia makes nerve and muscle more excitable.
Calcium matters for many systems, because it is needed for neuromuscular function, cardiac conduction and skeletal integrity. The symptoms of hypocalcemia are those of neuromuscular irritability. Tetany, a sustained involuntary muscle contraction, is the most familiar of them. Hypocalcemia also affects the heart. And when calcium stays low for a long time, the skin, brain and smooth muscle are affected as well.
Does the speed of the fall matter?
Yes. Symptoms depend on both the absolute calcium level and the rate at which it has fallen. The same value produces little in a slow decline and severe symptoms in a rapid one. Acute hypocalcemia declares itself quickly, through neuromuscular irritability and cardiac involvement.
What does acute hypocalcemia look like?
The main hallmark of acute hypocalcemia is neuromuscular irritability. It can range from local tingling of the fingertips and peri-oral region to paresthesias of the extremities.
The neuromuscular features are Chvostek’s sign, Trousseau’s sign, paresthesias, tetany, seizures (focal, absence or generalised), muscle cramps, muscle weakness, laryngospasm and bronchospasm.
Why do the spasms come on?
Spasm attacks can happen in acute hypocalcemia. Two of them, laryngospasm and bronchospasm, are a medical emergency.
What about the heart?
Apart from neuromuscular irritability, the other common manifestation of acute hypocalcemia is cardiac involvement. Low calcium prolongs the plateau phase of the cardiac action potential, and that lengthens the QT interval. The cardiac features are a prolonged QT interval on the ECG, congestive heart failure and cardiomyopathy.
What does chronic hypocalcemia look like?
In chronic hypocalcemia the picture is shaped by calcium deposited in tissue over time. The skin, brain and smooth muscle are affected. Acute and chronic hypocalcemia together produce a wide range of features, and they are easier to find when grouped by system.
What happens to the brain and eyes?
The neurological signs of chronic hypocalcemia include calcification of the basal ganglia and other areas of the brain. The neurological features are:
- extrapyramidal signs from calcification of the basal ganglia
- calcification of the cerebral cortex or cerebellum
- personality disturbance, irritability and impaired intellectual ability
- nonspecific EEG changes
- increased intracranial pressure
- parkinsonism, choreoathetosis and dystonic spasms
Mental status can change as well: confusion, disorientation, psychosis, fatigue, anxiety, poor memory and reduced concentration. The eyes show subcapsular cataracts and papilledema.
Why do the skin, hair and teeth change?
These are the ectodermal changes of long-standing hypocalcemia. They include dry skin, coarse hair, brittle nails, alopecia, atopic eczema and psoriasis, among others. Alopecia occurs mostly in surgically induced hypoparathyroidism and the autoimmune forms.
The full list of ectodermal features is dry skin, coarse hair, brittle nails, alopecia, enamel hypoplasia, shortened premolar roots, thickened lamina dura, delayed tooth eruption, increased dental caries, atopic eczema, exfoliative dermatitis, psoriasis and impetigo herpetiformis.
Why do the gut and airway get involved?
Smooth muscle is involved through irritability of the autonomic ganglia caused by hypocalcemia. This produces dysphagia, abdominal pain, biliary colic and wheezing. The smooth muscle features are dysphagia, abdominal pain, biliary colic, dyspnea and wheezing.
How are the signs elicited at the bedside?
Two bedside tests bring out the increased excitability of hypocalcemia: Chvostek’s sign and Trousseau’s sign.
Chvostek’s sign
Chvostek’s sign uses the hyper-responsiveness of muscle to a trigger. The facial nerve is tapped just anterior to the ear, at the angle of the jaw. The sign is positive if the patient’s ipsilateral facial muscles twitch or contract on tapping.
Trousseau’s sign
Trousseau’s sign uses the same increase in excitability of peripheral nerves. An inflation cuff is placed on the arm and kept inflated at least 20 mmHg above the patient’s systolic blood pressure for at least 3 minutes. The sign is positive if involuntary contraction of the metacarpophalangeal, thumb and wrist muscles occurs, called the carpal spasm. Trousseau’s sign has higher sensitivity and specificity than Chvostek’s sign for diagnosing hypocalcemia.
Once these signs suggest that calcium is low, how do you confirm it and find the cause?