Metabolic Bone Disease Flashcards
What is the composition of Bone
Composition of Bone
•INORGANIC (65%)
- Consists of calcium hydroxyapatite
- Stores 99% of total body calcium
•ORGANIC (35%)
- Bone cells and protein matrix
What is the classification of Bone?
- Lamellar = mature bone composed of parallel lamellae or concentric lamellae
- Woven = immature bone composed of irregularly arranged collagen fibres
Cortical and Cancellous describe the structures of the bone – these are both types of MATURE adult bone (i.e. they are both lamellar bone)
- Cortical bone – consists of parallel lamellae
- Cancellous bone – consists of concentric lamellae
Define Ossification, what are the different types?
The process of turning a structure into bone is called ossification
There are two main forms of ossification
- Intramembranous ossification – occurs in flat bones
- Endochondral ossification – occurs in long bones
What are the different types of Bone Biopsy?
Why would we conduct one?
Types
- Closed – core biopsy using a Jamshidi needle
- Open – used for sclerotic or inaccessible lesions
Indications
- Investigate bone pain or tenderness
- Investigate abnormality seen on X-ray
- Bone tumour diagnosis
- Determine cause of an unexplained infection
- Evaluate effectiveness of therapy
Define Metabolic Bone Disease and state the five most common
a group of diseases that cause a change in bone density and strength by increasing bone resorption, decreasing bone formation and altering bone structure. It may be associated with disturbances in mineral metabolism.
FIVE common MBDs
- Primary Hyperparathyroidism
- Rickets/Osteomalacia
- Osteoporosis
- Paget’s Disease
- Renal Osteodystrophy
Define Primary Hyperparathyroidism
Statet the main causes
What are the PTH actions
What would blood tests show on a patient like that?
What are the symptoms displayed
Increased secretion of PTH, unrelated to the plasma calcium concentration
Causes:
- Parathyroid adenoma (80%)
- Parathyroid hyperplasia (20%)
- Parathyroid cancer
- Familial syndromes (e.g. MEN-1)
Diagnosis:
Blood test will show:
- HIGH Ca2+
- LOW PO43-
- HIGH/NORMAL PTH
IMPORTANT: PTH should be LOW if Ca2+ is high
PTH actions:
- Increase resorption of bone (increased release of Ca2+ and PO43- from bone)
- Increased renal calcium reabsorption
- Increased renal phosphate excretion
- Increased calcitriol formation
Symptoms:
- Stones (Calcium oxalate renal stones)
- Bones (osteitis fibrosa cystica, bone resorption)
- Abdominal groans (acute pancreatitis)
- Moans (psychosis & depression)
Define Osteomalacia and Rickets
What are the actions of Vitamin D
What are the main causes of Ostemalacia/Rickets?
Definition: a lack of bone mineralisation leading to softening of bones, caused by a deficiency of Vitamin D or phosphate
- Rickets – in children (cartilaginous growth plate is affected)
- Osteomalacia – in adults
Vitamin D Actions:
- Intestine – increase Ca2+ and PO43- absorption
- Bone – increase bone resorption
- Kidneys – increase Ca2+ reabsorption and PO43- excretion
Causes:
- Poor dietary Vit D intake
- GI disturbance (e.g. malabsorption)
- Chronic renal failure
- Rare hereditary forms (e.g. defective vit D receptor)
- Renal phosphate loss can also cause osteomalacia/rickets (due to FGF-23 and Fanconi Syndrome)
What are the Radiological, Biochemistry and and clinical signs of Osteomalacia/ Rickets?
Osteomalacia/Rickets Biochemistry
- Low/Normal Ca2+
- Low PO43-
- High ALP
- Low calcitriol
- High PTH (secondary)
Signs of Osteomalacia/Rickets
- Bone pain/tenderness
- Fracture
- Proximal weakness
- Bone deformity
Radiological Signs:
- Looser’s Zones – transverse lucencies traversing part way through the bone, usually at right-angles to the cortex
- Codfish Vertebrae – biconcave vertebrae
- Metaphysis Changes – indistinct frayed metaphyseal margins and widened growth plate (only in Rickets, not osteomalacia)
- Bowing of the legs
- Rickety rosary (enlargement of anterior ribs)
Clinical Signs:
- Bone pain/tenderness
- Fracture
- Proximal weakness
- Bone deformity
Define Osteoporosis
State the main causes
How can diagnosis be mede?
Reduced bone density > 2.5 standard deviations below the peak bone mass achieved by healthy adults, resulting in bone fragility and increased risk of fractures
Causes
- Primary – age, post-menopausal (oestrogen has a protective effeect)
- Secondary – drugs (steroids), systemic disease (hyperparathyroidism, hyperthyroidism)
Diagnosis:
Define Renal Osteodystrophy
State the Biochemical Changes
An alteration in bone morphology in patients with chronic kidney disease
Biochemical Changes
- High PO43-
- Low calcitriol (1a-hydroxylate does not activate)
- Low Ca2+
- High PTH (secondary)
Define Paget’s Disease
State the symptoms
What are the most commopnly affected bones
A disorder of bone turnover that is common amongst the elderly
Symptoms: pain, microfractures, deafness, skull changes, warmth over affected area
Commonly affected sites: skull, vertebral column
What is Primary, Secondary and Tertiary Hyperparathyroidism?
TERTIARY hyperparathyroidism – the secondary hyperparathyroidism caused by renal failure will lead to parathyroid hyperplasia and, eventually, the parathyoid cells will stop responding to the Ca2+ feedback and become autonomous. This is tertiary hyperparathyroidism.
