Disorders of Calcium homeostasis Flashcards
What are the clinical manifestations of hypercalcaemia?
‘Stones, bones, abdominal moans and psychic groans’
Includes muscle weakness, central effects, renal effects, bone involvement, abdominal pain, and ECG changes.
What are the central effects of hypercalcaemia?
- Anorexia
- Nausea
- Mood change
- Depression
What renal effects are associated with hypercalcaemia?
- Impaired water concentration
- Renal stone formation
What ECG changes are seen in hypercalcaemia?
Shortened QT interval
What is factitious hypercalcaemia?
Raised [calcium] due to high plasma [albumin]
What are some causes of factitious hypercalcaemia?
- Venous stasis
- Dehydration
- IV albumin
What is the prevalence of primary hyperparathyroidism?
1 in 500 to 1 in 1000
In which decade is primary hyperparathyroidism most common?
6th decade
What is the gender ratio for primary hyperparathyroidism?
Women > men, 3:2 ratio
What is the most common etiology of primary hyperparathyroidism in outpatients?
90% solitary adenoma; hyperplasia; carcinoma (rare)
What distinguishes 1y hyperparathyroidism from 2y and 3y?
1y is autonomous overproduction of PTH; 2y is appropriate increase in PTH due to hypocalcaemia; 3y is rare overactivity of a 2y gland.
What are the diagnostic criteria for 1y hyperparathyroidism?
Raised Ca2+ with inappropriately increased PTH
What happens to phosphate and bicarbonate levels in 1y hyperparathyroidism?
They tend to be low in serum.
What imaging technique is used for parathyroid diagnosis?
Sestamibi scan (99m Tc-MIBI)
What is the acute treatment for high ionised calcium in 1y hyperparathyroidism?
- Re-hydration
- Drugs
What is the definitive treatment for 1y hyperparathyroidism?
Removal of parathyroid adenoma (surgery)
What drugs are used to treat hypercalcaemia?
- Bisphosphonates
- Furosemide
- Calcitonin
- Glucocorticoids
What is the mechanism of action for bisphosphonates?
Inhibit osteoclast action and bone resorption
What is the most common cause of hypercalcaemia in hospitalised patients?
Malignant disease
What percentage of cancer patients may develop hypercalcaemia?
20-30%
What are the two broad reasons for hypercalcaemia in malignancy?
- Endocrine factors secreted by malignant cells
- Metastatic tumour deposits in bone
What tumour types commonly cause hypercalcaemia?
- Lung (35%)
- Breast (25%)
- Haematological (14%)
- Head & Neck (6%)
- Renal (3%)
- Prostate (3%)
- Unknown primary (3%)
- Others (3%)
What is humoral hypercalcaemia of malignancy?
Caused by PTH-related peptide (PTHrP) secreted by solid tumours.
What diagnosis is indicated by raised Ca2+ with suppressed PTH?
Malignancy
What are the principles of treatment for malignant hypercalcaemia?
- Re-hydrate the patient
- Use drugs to lower calcium
- Treat underlying malignancy
What is familial hypocalciuric hypercalcemia (FHH)?
A rare condition where Ca2+ sensor on parathyroid glands is less sensitive to Ca2+ suppression of PTH.
In FHH, what happens to urine Ca2+ excretion?
Low relative to plasma Ca2+.
What is the summary of pathological hypercalcaemia?
Common condition, potentially life-threatening; usually due to primary hyperparathyroidism or malignant disease (>90%).
What is the predominant cause of clinical manifestations of hypocalcaemia?
Increase in neuromuscular excitability
This is often linked to increased inward Na+ movement.
List three neuromuscular symptoms of hypocalcaemia.
- Numbness and paraesthesiae
- Muscle cramps
- Bronchial or laryngeal spasm
What mental state changes can occur due to hypocalcaemia?
- Personality change
- Mental confusion
- Impaired intellectual ability
What is factitious hypocalcaemia?
A consequence of low plasma [albumin]
This can occur due to conditions such as malnutrition, liver disease, or nephrotic syndrome.
Name two conditions that can lead to low plasma albumin.
- Acute phase response
- Nephrotic syndrome
What are the causes of vitamin D deficiency?
- Lack of sunlight
- Inadequate dietary source
- Malabsorption
True or False: Chronic renal disease is a relatively rare cause of vitamin D deficiency.
False
Chronic renal disease is a relatively common cause.
What are the biochemical features of vitamin D deficiency?
- Low 25-D3 and 1,25-D3
- Low Ca2+
- High PTH
- Low phosphate
What pathological bone problem is associated with vitamin D deficiency?
Osteomalacia
In children, this condition is referred to as ‘Rickets’.
What is the consequence of osteoid laid down by osteoblasts not being adequately calcified?
Bones become softened, weak, and susceptible to fracture.
What are two inherited causes of osteomalacia?
- Deficient 1-hydroxylase
- Defective receptor for calcitriol
What symptoms are associated with hypoparathyroidism?
- Low Ca2+
- Inappropriately low PTH
- Increased phosphate
In acute situations, what treatment may be required for hypocalcaemia?
IV calcium
What is the common treatment for chronic hypocalcaemia?
- Oral calcium
- Vitamin D
- Magnesium (sometimes)
What is osteoporosis?
Commonest bone disease characterized by reduced bone mineral density and increased risk of fracture.
How is osteoporosis assessed?
Dual-energy X-ray absorptiometry (DEXA)
What distinguishes osteoporosis from osteomalacia?
- Osteoporosis: Normal histology, less bone, normal biochemistry
- Osteomalacia: Abnormal histology, uncalcified osteoid, abnormal biochemistry
Summarize the cause of pathological hypocalcaemia.
Most commonly due to calcitriol deficiency from nutritional or other causes.
What is the treatment approach for pathological hypocalcaemia?
Directed at the root cause, with therapeutic strategies to overcome hypocalcaemia.
