Hypofunction of anterior pituitary

Adenohypophyseal hypofunction is developed due to destruction of the anterior lobe of more than 75% because the anterior pituitary has a large functional reserve. Two important syndromes are: 1)panhypopituitarism and 2)dwarfism.

1. Panhypopituitarism. Three most common causes of panhypopituitarism are:

1. Non-secretory (chromophobe) adenoma, 2. Sheehan's syndrome and Simmond's disease, and 3) empty-sella syndrome.

Sheehan's syndrome it is pituitary insufficiency occurring due to postpartum pituitary necrosis. The main pathogenetic mechanism underlying Sheehan's necrosis is the enlargement of the pituitary occurring during pregnancy which may be damaged by hypotensive shock, DIC following delivery, traumatic injury to vessels, and excessive haemorrhage. The first clinical manifestation of Sheehan's syndrome is failure of lactation following delivery which is due to deficiency of prolactin.

The causes of Simmond's disease may be pituitary adenomas, pituitary surgery or radiation, ischemic necrosis, syphilis, tuberculosis, metastatic carcinoma, trauma ect.

The common signs of Sheehan's syndrome and Simmond's disease include loss of body (axillary and pubic) hair, amenorrhoea, sterility and loss of libido, premature aging, progressive emaciation, low blood pressure, fatigue, hyponatreamia. The sign of melanocyte-stimulating hormone loss is pallor. Concomitant deficiency of TSH and ACTH may result in hypothyroidism and adrenocortical insufficiency.

Empty-sella syndrome. Most commonly, it results from defect in diaphragma sella that allows the arachnoidea mater and cerebrospinal fluid to penetrate into the sella resulting compression of the pituitary Other less common causes are: Sheehan's syndrome, infarction and scarring, irradiation damage, or surgical removal of the gland.

       2) Pituitary dwarfism. Most commonly, isolated GH deficiency is the result of an inherited autosomal recessive disorder. Less often it may be due to a pituitary adenoma or craniopharyngioma, infarction and trauma to the pituitary. The clinical features of inherited cases appear after one year of age. These include proportionate retardation in growth of bones, normal mental state for age, poorly-developed genitalia, delayed puberty and episodes of hypoglycaemia.

       Hypofunction of posterior pituitary and hypothalamus is rare.

Deficient secretion of ADH causes diabetes insipidus. It can result from: inflammatory and neoplastic lesions of the hypothalamo-hypophyseal axis, destruction of neuro-hypophysis due to surgery, radiation, traumas of head. The main features are excretion of large volume of dilute urine of low specific gravity (below 1.010); serum sodium and osmolality are increased owing to excessive renal loss of free water resulting polyuria and polydipsia. May develop life-threatening dehydration.

Hyperpituitarism

Hyperpituitarism is characterised by oversecretion of one or more of the pituitary hormones.

Three common syndromes of adenohypophyseal hyperfunction are: gigantism and acromegaly, hyperprolactinaemia and Cushing's disease.

1. Gigantism and acromegaly. Both these clinical syndromes result from excess of growth hormone (GH), most commonly by somatotroph adenoma.

Gigantism is produced when GH excess occurs in prepubertal period. The main clinical feature in gigantism is the excessive and proportionate growth of the child. There is enlargement and thickening of the bones resulting in considerable increase in height and enlarged thoracic cage.

Acromegaly results when there is overproduction of GH in adults following cessation of bone growth and is more common than gigantism. The term 'acromegaly' means increased growth of extremities. There is enlargement of hands and feet, coarseness of facial features with increase in soft tissues, prominent supraorbital ridges and prognathism (a more prominent lower jaw and protrusion of the lower teeth in front of upper teeth). Other features include enlargement of the tongue and lips, thickening of the skin and kyphosis. Sometimes, may be thyrotoxicosis, and gonadotropin insufficiency causing amenorrhoea in the females and impotence in the male, generalized muscle weakness, hypertension, arthritis, congestive heart failure.

2. Hyperprolactinaemia is the excessive production of prolactin (PRL), most commonly by prolactinoma. Several classes of drugs can cause hyperprolactinaemia, including dopamine receptor antagonists such as neuroleptic drugs (phenothiazines, haloperidol) and antihypertensive drugs such as reserpine, which inhibit dopamine storage. Other causes of hyperprolactinaemia include estrogens, renal failure, and hypothyroidism. In the female, hyperprolactinaemia causes amenorrhoea-galactorrhoea syndrome characterized clinically by infertility and expression of milk from breast, not related to pregnancy or puerperium. In the male, it may cause impotence or reduced libido.

       3. Cushing's Disease or pituitary-dependent hypercortisolism (about 60-70% cases of hypercortisolism) results from АСTН excess. Most frequently, it is caused by corticotroph adenoma. The adrenal glands in patients with Cushing's disease are characterized by of nodular cortical hyperplasia caused by elevated levels of ACTH.