Hypocalcaemia

Section: Endocrine Sub-section: Parathyroid

Signs/Symptoms of Hypocalcaemia

• Acute manifestations
  • Tetany
  • Seizures
• Also get
  • Cardiac abnormalities
  • Papilloedema
  • Psychiatric – emotional instability, anxiety, depression
  • Fatigue
  • Hyperirritability

Tetany

• Uncommon unless Ca2+ < 1.1mmol/L
• Due to peripheral neuromuscular irritability
  • Hyperexcitable peripheral neurons
  • NB: Synergism with alkalosis
• Mild symptoms can cause anxiety, hyperventilation, exacerbation of symptoms
• Symptoms
  • Mild
    • Perioral numbness, peripheral paraesthesia, cramps
  • Severe
    • Carpopedal spasm, laryngospasm, seizures
  • Classic Findings
    • Trousseau’s sign (most specific)
      • Induction of carpal spasm by inflating BP cuff over systolic for 3 mins
      • Can also induce voluntarily with hyperventilation after cuff removal
    • Chvostek’s sign
      • Contraction of ipsilateral facial muscles by tapping on facial nerve just anterior to the ear
      • Can range from lip twitching to full spasm of all facial muscles
        • Can be present in 10% of normal people as well
    • NB: Both may be negative in patients with hypocalcaemia

Seizures

• Can be only presenting symptom
• If in absence of tetany may be due to low CSF Ca2+ rather than serum Ca2+
• Can get
  • Generalized tonic-clonic
  • Generalized absence
  • Focal seizures

Cardiovascular effects

• Decreased myocardial performance or CHF
• Myocardial dysfunction reversible with Ca2+
• Mechanism undefined
  • ? Ca2+ role in excitation-contraction coupling
  • Prolonged Q-T interval
  • Can get arrhythmias – but rare
  • Most severely can get Torsades-de-pointes
    • But less common than hypokalaemia or hypomagnesaemia

Treatment

• IV Ca2+ replacement if:
  • Symptomatic (Tetany, seizures, carpopedal spasm)
  • Prolonged Q-T
  • Or if Ca2+ < 1.9mmol/L
  • Rapid infusion
    • 1 or 2 g Calcium Gluconate in 50mL normal saline over 10-20mins
    • Followed by continued slow infusion
      • 10% Calcium Gluconate or 10% Calcium Chloride in normal saline (50mL/hr)
• Treat concurrent hypomagnesaemia
  • For mild/chronic cases
  • PO supplementation (Calcium Carbonate)
  • Don’t forget Vit D supplementation if required

Hypoparathyroidism

• Inadequate PTH secretion leads to
  • Hypocalcaemia
  • Hyperphosphataemia
• Most commonly a result of damage to normal glands
  • Post surgical or after reimplantation
• Can also be
  • Congenital
  • Pseudohypoparathyroidism

Congenital Hypoparathyroidism

• Extremely rare causes of hypoparathyroidism
  • Born without adequate parathyroid tissue (e.g. DiGeorge syndrome)
    • Caused by microdeletions occurring in chromosome region 22q11.2
    • Features vary widely and include:
      • Congenital heart defects
      • Defects in the palate
      • Facial anomalies
      • Recurrent infections
      • Learning disabilities
  • Hypoparathyroidism secondary to maternal hyperparathyroidism
    • Hyperparathyroidism during pregnancy associated with foetal complications in 80% of cases
  • Maternal hypercalcaemia results in suppression of foetal parathyroid glands > Foetal hypocalcaemia
    • Intrauterine growth retardation
    • Preterm delivery
    • Low birth rate
    • Foetal death
  • Most cases of neonatal hypoparathyroidism are transient
    • Respond to Ca2+ supplementation

Pseudohypoparathyroidism

• Rare metabolic condition
• Have low serum Ca2+ and hyperphosphataemia
  • PTH is appropriately elevated because of the hypocalcaemia
  • But body fails to respond to PTH
• Linked to a dysfunction of the Gsα subunit of G proteins (3 types)
• Type 1a (Albright Hereditary Osteodystrophy)
  • Characteristic phenotypic appearance
  • Short fourth and fifth metacarpals and a rounded facies
  • Associated with thyroid-stimulating hormone resistance
• Type 1b
  • Biochemically similar but lacks the phenotypic appearance
  • Associated with a methylation defect
• Type 2
  • Occur downstream of type 1a or 1b
  • A normal cAMP response to PTH stimulation occurs, despite the inherent abnormality in calcium regulation