hyperparathyroidism

Primary hyperparathyroidism

· syn. osteitis fibrosa cystica

definition

· disorder of calcium metabolism secondary to raised serum parathyroid hormone

· characterised by hypercalcaemia and hypophosphataemia

Epidemiology

· common endocrine disorder

· ranks behind diabetes and hyperthyroidism

· increased incidence due to routine analysis of calcium

· more common in old wome

· peak incidence in 70’s

· F:M = 3:2

· occurs in children as part of MEN I or II

aetiology

· excessive secretion of PTH by parathyroid with failure to respond to resultant excess calcium levels

· hyperfunction may be due to

· solitary adenoma (80%)

· hyperplasia of all glands (15%)

· carcinoma (3%)

· may be part of multiple endocrine neoplasia (MEN)

· MEN I is hyperparathyroidism with

· pituitary tumour

· pancreatic tumour (usually gastrinoma with Zollinger-Ellison syndrome, ie. peptic ulcer and gastric hypersecretion)

· MEN IIa is hyperparathyroidism with

· thyroid tumour (medullary)

· adrenal medulla tumour (phaeochromocytoma)

pathophysiology

· PTH enhances synthesis of 1,25-D

· PTH and 1,25-D together

· increase gastrointestinal absorption of calcium

· increase tubular reabsorption of calcium

· degrade bone by breakdown of hydroxyapatite crystals

· destroy bone by osteoclastic stimulation

· decrease tubular reabsorption of phosphate

PATHOLOGY

Histology

Osteitis fibrosa cystica

· fibrous replacement of marrow

· osteoclastic resorption of bone

· defective new bone formation

· new and incompletely mineralised lamellar bone trabeculae

· osteoblastic rimming

Brown tumour

· areas of brownish tumour like-masses in bone

· composed of

· granulation tissue

· inflammatory cells

· giant cells

· little bone at all

clinical

· usually middle-aged women

· age 40-65, M:F = 2:1

· may be incidental finding in asymptomatic patient

· classical presentation is

· stones (renal calculi)

· bones (bone pain and tenderness)

· groans (abdominal pain)

· moans (confusion and dementia)

· presentation usually much more subtle because of greater awareness and use of screening tests

· most common presentation is hypercalcaemia in presence of low back pain or osteopaenia

Renal

· polyuria and polydipsia

· renal calculi

· urinary tract infections

· impaired renal function

· renal failure

Bone

· pain

· deformity

· fracture

Psyche

· depression and lability

· confusion

· dementia

Gut

· anorexia and nausea

· abdominal cramps

· gastric ulcers

· pancreatitis

Other

· ectopic calcification

· proximal muscle weakness

INVESTIGATIONS

Biochemical

· elevated serum Ca++

· lowered serum PO₄--

· elevated serum ALP

· increased bone formation in response to destruction

· elevated serum urate

· increased tissue destruction

· elevated serum PTH

· special assays available

Radiology

Plain x-ray

Bone

· generalised osteopenia

· localised subperiosteal bone resorption

· best seen on radial border of middle phalanx of middle fingers

· erosion of

· outer 1cm of clavicle

· proximal humerus

· pubic symphysis

· sacro-iliac joints

· salt-and-pepper skull

· bone cysts

· osteitis fibrosa cystica

· brown tumours

· codfish vertebra

· compression fracture of verteba

· pathological fractures

Soft tissue

· renal calculi

· calcification in

· triangular fibrocartilage

· menisci

· articular cartilage

· chondrocalcinosis

MANAGEMENT

· principal role is in making diagnosis

· main treatment is

· reduction of hypercalcaemia

· surgical removal of parathyroid

Other

Secondary hyperparathyroidism

· oversecretion of PTH due to partial resistance to metabolic actions of hormone

· resistance to normal level of PTH leads to hypocalcaemia

· this leads to enlargement of parathyroids

· occurs in

· renal failure

· vitamin D deficiency (rickets)

· pseudohyperparathyroidism (deficient response to PTH at receptor)

Tertiary hyperparathyroidism

· development of pituitary adenoma due to secondary hyperplasia