Lecture 10: Calcium metabolism

Question 1

Primary hyperparathyroidism presentation?

Answer 1

Most often present with no specidic symtoms but rather eg:

• 60 y/o male with 2 year history of tiredness
• previous episode of haematuria
• no thirst, polyuria, constipation or bone pain
• Mildly elevated plasma calcium and ionized calcium
• mildly decreased GFR

Diagnosis made by PTH being raised

Question 2

Cancers causing hypercalcaemia?

Answer 2

• Solid tumours secreting PTHrP (eg. carcinoma of bronchus)
• Multiple skeletal metastasesm (eg. advanced breast cancer)
• Bone marrow malignancy -(secretion of cytokines stimulating bone resorption. eg. multiple myeloma)

Question 3

Diagnosis of humeral hypercalcaemia of malignancy?

Answer 3

PTH independent hypercalcaemia diagnosed by undetectable levels of PTH <0.2 when should be 1-6

AND

Parathyroid hormone-related peptide (PTHrP) is detectable in large amounts compared to the normal value of <1.3

Question 4

Treatment for humoral hypercalcaemia of malignancy

Answer 4

If possible then treat the underlying cancer

Paliation by bisphosphonates inhibit the osteoclastic bone resorption provides short to medium term relief from this component of the disease.

Question 5

Coeliac disease leading to Hypocalcaemia?

Answer 5

PTH will be high but serum 25 OH vitamin D is undetectable (normally lipid soluable). Faecal fat is extremely high indicating non-absorption.

Bloods show decreased calcium and markidly increased alkaline phosphatase.

folate, iron deficiency, anaemia, generalised muscle wasting and weight loss. On top of this osteomalacia from failure to mineralise bones correctly is all due to Vitamin D deficiency from coeliac disease.

Question 6

Classification of osteomalacia?

Answer 6

Calciopenic

• Low dietary Ca or malabsorption
• Low calcidiol or disordered VitD metabolism

Phosphopenic

• Disordered VitD metabolism
• increased renal phosphate loss (genetic or tumour)

Osteoblast dysfunction

• Aluminium
• Etidronate
• Hypophosphatasia

Question 7

Causes of Vitamin D deficiency?

Answer 7

1. inadequate exposure
2. enzyme induction (increased catabolism of precursors)
3. impaired 1a hydroxylase
4. poor diet or more importantly GI disease

Question 8

Diagnosis of pseudohypoparathyroidism (PTH resistance)?

Answer 8

Calcium is low and PTH is high showing an intact feedback loop

short in stature and short 4th and 5th metacarpal bones

Question 9

Hypocalcaemic, hypophosphatemic and sings of neuromuscular irritability? Differential?

Answer 9

Suggestive of hypoparathyroidism

Aquired:

• Post thyroid surgery
• hypomagnesaemia
• Iron overload (thalassaemia)
• Rare associations: lupus, systemic sclerosis, Wilson’s disease

Idiopathic/Genetic syndromes

Question 10

Autosomal dominant hypercalciuric hypocalcaemia? Treatment?

Answer 10

ADHH

Constitutive activation of CaSR reading the ECF levels are higher than they are leading to low PTH even in low Ca. Difficult to distinguish from idiopathic hypoparathyroidism (see family history)

Relative hypercalciuria

No treatment if asymptomatic -risk increasing hypercalciuria with nephrocalcinosis if treated with Vitamin D

Small doses of Vitamin D will help to keep calcium at an asymptomatic value.

Question 11

FHH is? suspect if? diagnose by?

Answer 11

Familial hypocalciuric hypercalcemia

Suspect if:

• PTH in normal range
• Family history of hypercalcemia

Diagnose by:

• Screening immediate relatives
• Ratio of fasting urine calcium to creatinine clearance (vitamin D replete, no thiazides) - relative hypercalcuria
• CaR genotyping