4th April 2024

Hypoparathyroidism

This is characterised by hypocalcaemia, hyperphosphatemia and low/inappropriately normal levels of PTH. In pseudohypoparathyroidism, the findings are similar but PTH is raised due to resistance. Some patients remain asymptomatic with low serum calcium levels. Symptoms related to hypocalcaemia include:

• Tetany: muscle twitches, cramps, or spasms
• Perioral, hand and feet paraesthesia
• Altered mental state 
• Generalised seizures: may indicate acute or severe hypocalcaemia
• Trousseau’s sign: painful clasping of fingers and hands when blood pressure cuff is inflated
• Chvostek’s sign: tapping the facial nerve in front of the ear elicits ipsilateral facial muscle contraction

Aetiology

Primary hypoparathyroidism is a result of relative or absolute PTH deficiency and occurs most commonly post-neck surgery. Rare causes include infiltrative or destructive diseases such as tumours, autoimmune destruction, heavy metal deposition (iron/copper), or genetic syndromes such as Di George syndrome.

Pseudohypoparathyroidism occurs due to defective PTH receptors or resistance to PTH. It is an autosomal dominant condition characteristically associated with a short stature, round face, dental hypoplasia and short 4th and 5th metacarpals. PTH levels are intact or highly elevated, distinguishing it from primary hypoparathyroidism. 

In pseudopseudohypoparathyroidism patients have the characteristic phenotype of pseudohypoparathyroidism (known as Albright’s hereditary osteodystrophy) with normal biochemistry.

Diagnostics

Diagnosis requires confirmed hypocalcaemia with low levels of PTH and the absence of hypomagnesaemia. Reversible causes of hypoparathyroidism include hypomagnesaemia, iron or copper overload. Investigations for specific causes of hypoparathyroidism, as mentioned above, may be considered. Table 2 shows the typical biochemical findings in primary, pseudohypoparathyroidism and pseudopseudohypoparathyroidism. 

Table 2: Typical biochemistry findings in hypoparathyroidism

Management

Acute, symptomatic hypocalcaemia is a medical emergency, therefore immediate intravenous replacement with close ECG monitoring is crucial as severe hypocalcaemia can cause prolonged QT interval and tachyarrhythmias.  Investigation for and treatment of hypomagnesemia (which may exacerbate hypocalcaemia) should also be commenced.

In patients with minimal symptoms, oral supplementation and ensuring vitamin D stores are replete, may be suitable. The signalling defect in pseudohypoparathyroidism is incurable, therefore maintenance of normal calcium and phosphate through supplementation is key. 

Patients undergoing neck surgery with a risk of parathyroid gland interference should have serum calcium levels checked immediately postoperatively and prior to discharge, with initial supplementation recommended.