HyperParathyroidism

Aetiology:

Hyperfunction of the parathyroid may result from

1. Primary hyperparathyroidism: usually due to a parathyroid adenoma (up to 90%), or hyperplasia (10%) including MEN I & II syndromes and rarely carcinoma (<5%)>

2. Secondary hyperparathyroidism: hyperplasia usually in response to hypocalcaemia as in chronic renal failure; less commonly e.g. Vitamin D deficiency, intestinal malabsorption, calcitonin producing tumour, pseudo-hypoparathyroidism

3. Tertiary hyperparathyroidism: where a functioning autonomous adenoma arises in the hyperplastic glands of secondary hyperparathyroidism; includes ectopic secretions PTH-like-substance by non-parathyroid tumours (e.g. lung, renal and ovarian cancer)

Parathyroid adenoma:

• Typically solitary (suspect nodular hyperplasia if >1)

• Most in inferior glands (may be ectopic and difficult to locate)

• Usually chief cell type, monoclonal origin; rarely associated with MEN I

• Most are sporadic; of these 25% have similar mutation to familial forms on chromosome 11.

Parathyroid hyperplasia:

• Typically involves all glands (may be asymmetrical)

• Mainly chief cells, may have a nodular pattern, polyclonal origin

• May be familial (homozygous loss of suppressor gene on chromosome 11, MEN I or less commonly MEN IIa)

Parathyroid carcinoma:

• Very rare, variable size

• Diagnosis difficult (require invasion  metastasis)

• Normally slowly progressive

Consequences and complications:

Hyperparathyroidism   PTH   serum Ca²⁺ levels (hypercalcemia)  metastatic calcification in kidneys, blood vessels, lungs, gastro-intestinal tract, skin conjunctiva etc.

Characterized by ‘painful bones, renal stones, abdominal groans’ and psychic moans’ with:

• Resorption of bone leading to osteoporosis or osteitis fibrosa cystica, collections of osteoclasts with haemorrhage (‘brown tumours’) and possibly pathological fractures.

• Renal stone formation is a feature of hypercalcemia and may interfere with renal function (nephrocalcinosis).

• Gastrointestinal disturbances including constipation, peptic ulcers, pancreatitis and gall stones.

• Central nervous system alterations (emotional disorders) including depression and lethargy.

(May also exhibit muscle atrophy)

Category: Pathology Notes