Hypocalcaemia

I am sure there are many medical students who have read about this over and over again but may not have seen it. I take this opportunity to share one of my patients who has hypocalcaemia secondary to Albright Hereditary Osteodystrophy(very very rare cause) and in paeds. Actually he is followed up in paeds and was incidentally admitted to my ward because of low calcium. I elicited Chvostek's sign in him and immediately treated his hypocalcaemia

Symptoms

Symptoms generally correlate with the magnitude and rapidity of the fall in serum calcium: mild hypocalcaemia (2.00-2.12 mmol/l) can be asymptomatic whereas acute symptoms of neuromuscular irritability can develop in the more severe form(<1.9>

• Paraesthesia (usually fingers, toes and around mouth)
• Tetany
• Carpopedal spasm (wrist flexion and fingers drawn together)
• Muscle cramps

Signs

• Chvostek's sign (tapping over facial nerve causes facial muscles to twitch) Note: this may be present in some normocalcaemic individuals. (refer video)
  
• Trousseau's sign (carpopedal spasm after inflating a BP cuff on the upper arm) (refer video)
  
• Seizures
• Prolonged QT interval which may progress to VF or heart block
• Laryngospasm
• Bronchospasm

With prolonged hypocalcaemia

• Sub-capsular cataract
• Papilloedema
• Abnormal teeth
• Ectopic calcification (for example, in basal ganglia may cause extrapyramidal neurological symptoms)
• Dementia and confusion

Aetiology

Causes of true hypocalcaemia fall into two main classes:

With low PTH levels (hypoparathyroidism)

• Parathyroid agenesis- alone or along with other abnormalities e.g. Di George syndrome
• Parathyroid destruction- due to surgery, radiotherapy, infiltration by metastases or systemic disease
  
• Autoimmune
• Reduced parathyroid secretion - due to gene defects, hypomagnesaemia, neonatal hypocalcaemia (may be due to maternal hypercalcaemia), hungry bone disease (after parathyroidectomy), mutation in calcium-sensing receptor.

With high PTH levels (secondary hyperparathyroidism)

• Vitamin D deficiency- due to nutritional lack, malabsorption, liver disease, receptor defects
• Vitamin D resistance (rickets)- renal tubular dysfunction (Fanconi's syndrome) or receptor defect
• PTH resistance - pseudohypoparathyroidism, hypomagnesaemia

Important other causes

• Hyperventilation
• Drugs- calcium chelators (citrate in blood transfusion); bone resorption inhibitors (bisphosphonates, calcitonin, plicamycin); drugs affecting vitamin D (phenytoin, ketoconazole), foscarnet
• Acute pancreatitis
• Acute rhabdomyolysis - usually in relation to crush injuries
• Malignancy - tumour lysis(following chemotherapy) or osteoblastic metastases (most common in prostate and breast cancers)
• Toxic shock syndrome

Commonest causes are hypoparathyroidism (frequently following surgery), vitamin D deficiency or abnormal metabolism, renal failure, hypomagnesaemia.
Hypocalcemia is extremely common in patients in hospital and correlates with the severity of their illness.³

Differential diagnosis

	Serum phosphate	Serum PTH	Serum ALP	Other
Renal failure	Raised	Raised	Raised	Raised creatinine
Hypoparathyroidism	Raised	Low/undetectable		Normal Vitamin D metabolites
Pseudohypoparathyroidism	Raised	Raised
Vitamin D deficiency or malabsorption	Low	Raised	Raised	Raised 25 (OH)D3 levels

• Hypoalbuminaemia - correct for albumin
• Consider drug therapy, malignancy, acute pancreatitis and rhabdomyolysis

Investigations

• Is the patient really hypocalcaemic? (Ideally take fasting blood specimens, uncuffed -remove tourniquet after needle in vein, but before taking blood sample). Ensure use an adjusted calcium value
• Exclude renal failure (check U&Es), acute pancreatitis (check amylase), rhabdomyloysis (check serum CK)
• Estimate serum magnesium
• Estimate serum PTH
• Evaluate Vitamin D metabolism

Always assess the patient clinically. Patients vary: some may be symptomatic within the normal reference range since there are narrow individual ranges within the normal reference range.

Management

Acute hypocalcaemia

• Treat where symptomatic (seizures, tetany) or at high risk of complications with a serum calcium <1.90>
• Give calcium gluconate IV 10 ml (2.25 mmol) of calcium gluconate 10% by slow injection. Repeat as necessary or follow with infusion of calcium gluconate 10% infusion - 40 ml (9 mmol)/24 hours.
• Monitor serum calcium concentrations regularly to judge response.
• If likely to be persistent, give vitamin D by mouth.
• If hypomagnesemic, necessary to correct magnesium level before the hypocalcaemia will resolve.

Extracted from http://www.patient.co.uk/showdoc/40001110/