When infants lack vitamin D, blood calcium levels decrease. If the parathyroid function is insufficient to compensate and cannot mobilize bone calcium, blood calcium cannot be maintained at normal levels. When serum calcium falls below 1.75 mmol/L, neuromuscular excitability increases, leading to symptoms such as convulsions and tetany. Therefore, this condition is also known as vitamin D deficiency tetany.

bubble_chart Clinical Manifestations

Infants primarily present with afebrile convulsions. The frequency of convulsive episodes ranges from 1 to 20 times per day, with each episode lasting from a few seconds to approximately half an hour. During convulsions, most patients lose consciousness, exhibiting rhythmic twitching of the hands and feet, facial muscle spasms, upward rolling of the eyes, and {|###|}urinary incontinence{|###|}. In young infants, sometimes only facial muscle twitching is observed, which represents the initial stage [first stage] symptom of the condition. Between episodes, the child's mental state is generally normal. Older infants or children primarily exhibit hand and foot convulsions, characterized by wrist flexion, finger extension, the thumb pressing close to the palm, and stiff toes with the {|###|}metatarsus{|###|} slightly arched. Consciousness remains clear during these episodes. Laryngospasm is the most severe manifestation of infantile hand and foot convulsions, which may present as inspiratory stridor and difficulty breathing. In severe cases, it can lead to death due to asphyxia. Intramuscular injections may occasionally induce laryngospasm.

Latent signs

The condition is referred to as latent hand and foot convulsions when only the following latent signs are present without convulsions or hand and foot convulsions. 1. Facial nerve sign (Chvostek's sign): Lightly tapping the facial nerve in front of the ear with a fingertip may elicit twitching of the eyelid or upper lip. A positive sign during the neonatal period has no diagnostic significance. 2. Peroneal reflex positivity: Tapping the peroneal nerve at the head of the fibula on the lateral side of the knee with a small hammer causes the foot to contract outward, indicating a positive result. 3. Tourniquet sign (Trousseau's sign): A blood pressure cuff is wrapped around the upper arm and inflated to temporarily stop the radial pulse. If hand convulsions occur within 5 minutes, the result is positive.

Serum calcium may be below

1. 75mmol/L, alkaline phosphatase is elevated, and serum phosphorus may be low or normal or elevated

bubble_chart Diagnosis

Age, Season, and Predisposing Factors: Over 85% of cases occur in infants under 1 year old, with the majority being under 6 months. The disease is most prevalent in spring (March to May). Vitamin D deficiency, inadequate dietary calcium, premature birth, and formula-fed infants are more susceptible.

bubble_chart Treatment Measures

﹝Treatment﹞

(I) Emergency Measures Laryngospasm and convulsions can lead to respiratory arrest, both of which are life-threatening and require immediate emergency treatment. 1. **Treatment for Laryngospasm** First, pull out the tongue, perform artificial respiration or administer pressurized oxygen. If necessary, perform endotracheal intubation. 2. **Management of Convulsions** Immediately administer an adequate dose of phenobarbital sodium (8 mg/kg intramuscularly); or paraldehyde (1 ml per year of age, with a maximum dose not exceeding 5 ml per administration) via deep intramuscular injection; or 10% chloral hydrate (4–10 ml) as a retention enema; or diazepam (0.1–0.3 mg/kg per dose) via intramuscular or intravenous injection. Simultaneously, perform acupuncture at the philtrum, Hegu (LI4), Shaoshang (LU11), and Yintang (EX-HN3) points. (II) **Calcium Supplementation** Do not wait for blood calcium test results. Immediately administer 10% calcium gluconate (5–10 ml) diluted with 10–20% glucose solution (10–20 ml) via slow intravenous injection (avoid subcutaneous or intramuscular injection, as it may cause local necrosis). Monitor heart rate during administration; if bradycardia occurs, slow the injection rate or stop it. Administer 1–3 times daily for 2–3 consecutive days. After spasms cease, switch to oral 10% calcium chloride (which both supplements calcium and acidifies the blood) at 5–10 ml, 3–4 times daily. After 7–10 days, switch to calcium lactate at 2 g daily. Avoid prolonged use of calcium chloride to prevent iatrogenic acidosis. (III) **Vitamin D Therapy** After 3–5 days of calcium supplementation, begin vitamin D supplementation, starting with a small dose to avoid inducing hypocalcemia. The dose is 2,500–5,000 IU/day, increasing to 5,000–10,000 IU/day after one week. The treatment duration is the same as for rickets, after which switch to a preventive dose. If necessary, administer a single intramuscular injection of vitamin D2 or D3 (300,000–600,000 IU) several days after calcium therapy. (IV) **If Seizures Persist After the Above Treatments** Measure serum magnesium levels. If serum magnesium is <0.75 mmol/L, administer 25% magnesium sulfate (0.1 ml/kg per dose intramuscularly) every 6 hours. After one day, switch to oral magnesium at 3 mg/(kg·d), divided into 3–4 doses daily.

bubble_chart Prevention

bubble_chart Differentiation

(1) Differential Diagnosis with Convulsive Disorders 1. Infantile Spasms Onset typically occurs between 3 to 7 months after birth. Seizures are accompanied by brief loss of consciousness and distinctive postures, often affecting intelligence. The EEG shows a characteristic "hypsarrhythmia" pattern. 2. Hypoparathyroidism Conditions such as transient neonatal hypoparathyroidism, accidental removal of the parathyroid glands during surgery, or primary hypoparathyroidism can lead to symptoms of hypocalcemia. However, this condition is characterized by elevated blood phosphorus, normal alkaline phosphatase, and decreased PTH levels, often requiring parathyroid hormone therapy. 3. Others It is also necessary to differentiate from convulsions caused by birth trauma, cerebral dysplasia, nervous system infections, cerebral symptoms of infectious diseases, as well as hypoglycemia, lead poisoning, etc. (2) Differential Diagnosis with Other Diseases Causing Tetany

1. Alkalotic Tetany Conditions such as hypochloremic alkalosis, respiratory alkalosis, or excessive infusion of alkaline solutions can increase calcium binding to proteins, reducing ionized calcium and leading to tetany. 2. Hypomagnesemic Tetany Seen in children with chronic diarrhea or prolonged intravenous therapy without magnesium supplementation. It should also be considered in cases where hypocalcemic convulsions are suspected but calcium therapy is ineffective. Blood magnesium levels may drop below 0.75 mmol/L, and symptoms can be controlled with magnesium injections or oral supplements. 3. Tetany Due to Chronic Renal Insufficiency Reduced phosphorus excretion leads to elevated blood phosphorus, which inhibits the conversion of 25-(OH)D to 1,25-(OH)₂D, resulting in hypocalcemia. However, hypoalbuminemia and chronic acidosis in this condition may not necessarily lead to very low ionized calcium levels. Tetany typically occurs only when serum calcium is extremely low or after alkaline fluid infusion. (3) Differential Diagnosis with Laryngeal Obstruction Diseases Laryngospasm should be differentiated from congenital laryngeal stridor. The latter primarily presents with inspiratory stridor. Mild cases exhibit intermittent stridor and are easily distinguishable, while severe cases involve persistent stridor accompanied by inspiratory difficulty, requiring blood calcium measurement for differentiation.