Metabolic Bone Diseases (except Osteoporosis And Osteomyelitis)

Question 1

Paget’s disease(osteitis deformans)

Answer 1

• described by sir James Paget (1876)
• incidence increases with age
• any bone may be involved
• common in spine, skull, pelvis and femur

Pathological features

• increased osteoclastic bone resorption followed by compensatory bone formation (overall increase in bone turnover)
• bone is softer, thicker and prone to pathological fractures

Clinical presentation
- usually asymptomatic
Diagnosis
- may be an incidental finding on x Ray / raised alkaline phosphate see (ALP) found on investigation of other pathologies
- increased bone thickness may be the only symptom / sign the patient complains of
- subcutaneous bones may be deformed, classically the tibia when it becomes sabre-shaped
- pain may be present but is unusual. It may represent high turn over at the time/more likely a pathological fracture
- in known paget’s patients, pain must be taken seriously as it may be a marker of sarcomatous change in the bone

• serum calcium and and phosphorus are normal
• alkaline phosphatase (ALP) is high (due to increased osteoblasts activity)
• Urinary excretion of hydroxyproline is high (increases bone turnover)
• isotope bone scan shows hot spots in affected areas
• x Ray shows both sclerosis and osteoporosis
• the cortex is thickened and the bone deformed
• pathological fractures
• the normal bone architecture is replaced by coarse trabecular pattern

Complications

• pathological fractures
• osteosarcomatous change (less than 5% and the prognosis is very poor)
• high output cardiac failure may develop due to increased vascularity of Paget’s bone (the bone acts as a arteriovenous fistula)
• deafness- bone deformation in the ear may cause nerve damage
• Osteoarthritis
• leonitiasis ossea: thickening of facial bones (rare)
• paraplegia due to cerebral involvement (rare)

Treatment

• squally no treatment required
• fracture will heal normally but bone deformity with a fracture may be a difficult challenge!
• drugs that reduce bone turnover such as calcitonin(lowers blood Ca)/ bisphosphonates are effective in relieving pain and may also relieve neurological complications such as deafness

Question 2

Osteitis fibrosa cystica

Answer 2

A complication of hyper-parathyroidism in which the bones turn soft and deformed

Etiology

• PTH regulates calcium use and removal from the body
• PTH helps control calcium, phosphorus and vitamin d levels within the blood and bone
• hyperparathyroidism may lead to increased bone breakdown, which can cause bones to turn soft
• Parathyroid cancer may cause osteitis fibrosa (rare)

Clinical presentation

• may cause bone pain/tenderness/fractures(arms, legs, spine)/other bone problems
• hyperparathyroidism may cause nausea, constipation, fatigue, and weakness

Diagnosis

• blood tests show high level of calcium, PTH, and ALP
• phosphorus may be low
• x ray may show thin bones, fractures, bowing and cysts
• teeth x Ray may also be abnormal
• people with parathyroidism are more likely to have osteopenia(thin bones)/ osteoporosis (very thin bones) than to have full blown osteitis fibrosa

Treatment

• most of the bone problems may be reversed by removing theabnormal parathyroid glands
• people may choose not to have surgery and instead be followed through blood tests and bone measurements
• if surgery is not possible, drugs may sometimes be used to lower calcium levels

Complications

• bone fractures
• deformities
• pain
• problems caused by hyperparathyroidism such as kidney stones and failure

Question 3

Renal osteodystrophy

Answer 3

Renal osteodystrophy (ROD), also known as uremic osteopathy, is the constellation of musculoskeletal abnormalities that occur in patients with chronic renal failure, due to concurrent and superimposed:
• osteomalacia (adults) / rickets (children)
• secondary hyperparathyroidism: abnormal calcium and phosphate metabolism
o bone resorption
o osteosclerosis
o soft tissue and vascular calcifications
o brown tumours
• aluminum intoxication, e.g. if the patient is on dialysis

Imaging findings are many and varied:
• osteopenia: (often seen early) thinning of cortices and trabeculae
• demineralization: usually subperiosteal, however it may also involve joint margins, endosteal, subchondral, subligamentous areas, cortical bone, or trabeculae
• subperiosteal resorption: characteristic subperiosteal resorption may be seen on radial aspects of middle phalanges of index and long fingers
• bone sclerosis
o diffuse bony sclerosis
o rugger-jersey spine: sclerosis of the vertebral body end plates
• soft tissue calcification
• amyloid deposition: erosion in and around joint
• insufficiency fractures

Treatment for renal osteodystrophy includes the following:
• calcium and/or native vitamin D supplementation
• restriction of dietary phosphate (especially inorganic phosphate contained in additives)
• phosphate binders such as calcium carbonate, calcium acetate
• active forms of vitamin D (calcitriol)
• renal transplantation
• hemodialysis five times a week is thought to be of benefit
• parathyroidectomy for symptomatic medication refractive end stage disease