Calcium homeostasis disorders

What is hyperparathyroidism?

Excessive secretion of parathyroid hormone (PTH) causing high calcium levels - hypercalcemia

What causes hyperparathyroidism?

• typically caused by parathyroid adnoma - a bengign tumour on the parathyroid hormone or can be cause by hyperplasia of gland or carcinoma (rarely)

Secondary cause

• compensatory PTH release due to chronic low levels of caclium and vitamin D

• chronic kidney disease causes phosphate retention, low calcium and increase PTH

• Vitamin D deficiency means calcium not absorbed - increase in PTH

What do we see in terms of blood in hyperparathyroidism?

• parathyroid hormone secretion increases causes:

  • Increased bone reabsorption

  • increased renal calcium reabsorption

  • Increased activation of vitamin D

• leads to hypercalcaemia

What are the consequences / symptoms of hyperparathyroidism?

• bone fractures, bone pain from bone reabsorption - bone cysts or lesions may also occur as a result

• lethargy, excessive thirst, anorexia, polyuria, heart block

• Hypercalciuria leads to kidney stones

• GI - nausea, constipation, peptic ulcers

• fatifue and depression

How do we treat hyperparathyroidism?

1st line - surgery - surgical removal of overactive tissue

Cinacalcet - lowers parathyroid hormone if surgery cannot be performed

correct underlying causes of hyperparathyroid hormone e.g.

• vitamin D analogues e.g. calcitriol, alfacalcidol

What is hypoparathyroidism?

Hypoparathyroidism is inadequate parathyroid hormone release which causes low calcium levels (hypocalcaemia) and high phosphate levels (hyperphosphatemia)

What causes hyperparathyroidism?

• damage to thyroid hormone during surgery

• autoimmune conditions

• genetic

What do we see in terms of the pathophysiology of hypoparathyroidism?

Low parathyroid hormone results in:

• low bone reabsorption → less calcium release

• Low renal calcium reabsorption → more calcium excreted

• Low activation of vitamin D → Low GI calcium absorption

Result - hypocalcemia, hyperphosphatemia

What symptoms do we see in hypoparathyroidism?

• symptoms due to low calcium levels

• Hyperexcitability of nerves - pins and needles, muscle spasms, and cramps, seizures and convulsions

• chvostek sign - twitching of facial muscles

• dental abnormalities

• dry scaly skin

• brittle hair and nails

• cataracts

How do we treat hypoparathyroidism?

• vitamin D supplements to enhance Ca2+ reabsorption and utilisation

• oral calcium supplements

What is pagets disease?

Excessive osteoclastic activity which increase bone breakdown, followed by disorganised osteoblastic repair - bone is dense but structurally weak leading to enlarged, deformed bones prone to fracture

Commonly affects the skull, pelvis, spine, femur and tibia

How do we treat pagents disease?

Bisphosphonates e.g. zoledronic acid IV given to reduce osteoclast activity

vitamin D and calcium - support bone health (as patients prone to fractures)

pain management

What is rickets?

Caused by vitamin D deficiency - vitamin D deficiency in children causes rickets but in adults causes osteomalacia

Rickets causes bowed legs due to inadequate vitamin D, meaning hypocalcaemia as calcium requires vitamin D for absorption

How do we treat rickets?

• dietary prevention

• calcium and vitamin D supplementation

• e.g. calcichew D3 tablets

• colecalciferol - vitamin d3

Note vitamin D also called calcitriol of cholecalciferol