Page 832 - Textbook of Pathology, 6th Edition

816 HYPERPARATHYROIDISM
Hyperfunction of the parathyroid glands occurs due to
excessive production of parathyroid hormone. It is classified
into 3 types—primary, secondary and tertiary.
Primary hyperparathyroidism occurs from oversecretion of
parathyroid hormone due to disease of the parathyroid
glands.
Secondary hyperparathyroidism is caused by diseases in
other parts of the body.
Tertiary hyperparathyroidism develops from secondary
hyperplasia after removal of the cause of secondary
hyperplasia.

Primary Hyperparathyroidism
Primary hyperparathyroidism is not uncommon and occurs
more commonly with increasing age. It is especially likely
to occur in women near the time of menopause.

ETIOLOGY. Common causes of primary hyperpara-
thyroidism are as follows:
1. Most commonly, parathyroid adenomas in approxi-
mately 80% cases.
Figure 27.20 Role of parathormone in regulating calcium metabo- 2. Carcinoma of the parathyroid glands in 2-3% patients.
lism in the body.
3. Primary hyperplasia in about 15% cases (usually chief
cell hyperplasia).
of parenchymal cells and variable amount of stromal fat. The Also included above are the familial cases of multiple
parenchymal cells are of 3 types: chief cells, oxyphil cells and endocrine neoplasia (MEN) syndromes where parathyroid
water-clear cells. The chief cells are most numerous and are adenoma or primary hyperplasia is one of the components.
SECTION III
the major source of parathyroid hormone. The latter two CLINICAL FEATURES. The patients with primary hyper-
types of cells appear to be derived from the chief cells and parathyroidism have the following characteristic biochemical
have sparse secretory granules but are potentially capable abnormalities:
of secreting parathyroid hormone. 1. Elevated levels of parathyroid hormone
The major function of the parathyroid hormone, in
conjunction with calcitonin and vitamin D, is to regulate 2. Hypercalcaemia
3. Hypophosphataemia
serum calcium levels and metabolism of bone. Parathyroid 4. Hypercalciuria
hormone tends to elevate serum calcium level and reduce
serum phosphate level. Secretion of parathyroid hormone Clinical presentation of individuals with primary hyper-
takes place in response to serum levels of calcium by a parathyroidism may be in a variety of ways:
feedback mechanism—lowered serum calcium stimulates 1. Most commonly, nephrolithiasis and or/nephrocalcinosis
Systemic Pathology
secretion of parathyroid hormone, while elevated serum (page 690). These dysfunctions result from excessive
calcium causes decreased secretion of the hormone. The role excretion of calcium in the urine due to hypercalcaemia
of parathyroid hormone in regulating calcium metabolism induced by increased parathyroid hormone level.
in the body is at the following 3 levels (Fig. 27.20): 2. Metastatic calcification, especially in the blood vessels,
1. Parathyroid hormone stimulates osteoclastic activity and kidneys, lungs, stomach, eyes and other tissues (page 53).
results in resorption of bone and release of calcium. Calci- 3. Generalised osteitis fibrosa cystica due to osteoclastic
tonin released by C-cells, on the other hand, opposes resorption of bone and its replacement by connective tissue
parathyroid hormone by preventing resorption of bone and (page 835).
lowering serum calcium level. 4. Neuropsychiatric disturbances such as depression, anxiety,
2. Parathyroid hormone acts directly on renal tubular epithe- psychosis and coma.
lial cells and increases renal reabsorption of calcium and 5. Hypertension is found in about half the cases.
inhibits reabsorption of phosphate; calcitonin enhances renal
excretion of phosphate. 6. Other changes such as pancreatitis, cholelithiasis and
3. Parathyroid hormone increases renal production of the peptic ulcers due to hypercalcaemia and high parathyroid
most active metabolite of vitamin D, i.e. 1, 25-dihydrocholecalci- hormone level are less constant features.
ferol, which in turn increases calcium absorption from the
small intestine. Secondary Hyperparathyroidism
The major parathyroid disorders are its functional Secondary hyperparathyroidism occurs due to increased
disorders (hyper- and hypoparathyroidism) and neoplasms. parathyroid hormone elaboration secondary to a disease