HYPERPITUITARISM; HYPER FUNCTION OF PITUITARY
Hyperpituitarism is characterized by oversecretion of one or more of the pituitary hormones. Such hypersecretion may be due to diseases of the anterior pituitary, posterior pituitary or hypothalamus.
A. Hyper function of Anterior Pituitary causing Hyperpituitarism:
Three common syndromes of adenohypophyseal hyperfunction are: gigantism and acromegaly, hyperprolactinemia, and Cushing’s syndrome.
GIGANTISM AND ACROMEGALY.
Both these clinical syndromes result from sustained excess of growth hormone (GH), most commonly by somatotroph (GH-secreting) adenoma.
When GH( growth hormone) level increases before epiphyseal closure, then gigantism is produced. Gigantism, therefore, occurs in boys and girls of prepubertal category and occurs less frequently than acromegaly. The main clinical feature in gigantism is the excessive and proportionate growth of the child. There is enlargement as well as thickening of the bones resulting in a 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 (acro=extremity).
There is enlargement of hands and feet, the coarseness of facial features with an increase in soft tissues, prominent supraorbital ridges, and a more prominent lower jaw which when clenched results in protrusion of the lower teeth in front of upper teeth (prognathism). Other features include enlargement of the tongue and lips, thickening of the skin, and kyphosis.
Sometimes, a few associated features such as TSH excess resulting in thyrotoxicosis, and gonadotropin insufficiency causing amenorrhoea in the females and impotence in the male, are found.
Hyperprolactinemia is the excessive production of prolactin (PRL), most commonly by lactotroph (PRL-secreting) adenoma, also called prolactinoma. Occasionally, hyperprolactinemia results from hypothalamic inhibition of PRL secretion by certain drugs (e.g. chlorpromazine, reserpine, and methyl-dopa).
In the female, hyperprolactinemia causes amenorrhoea-galactorrhoea syndrome characterized clinically by infertility and expression of a drop or two of milk from the breast, not related to pregnancy or puerperium. In the male, it may cause impotence or reduced libido. These features result either from associated inhibition of gonadotropin secretion or interference in gonadotropin effects.
Pituitary-dependent Cushing’s syndrome results from ACTH excess. Most frequently, it is caused by corticotroph (ACTH-secreting) adenoma.
B. Hyper function of Posterior Pituitary and Hypothalamus causing Hyperpituitarism:
Lesions of posterior pituitary and hypothalamus are uncommon. Two of the syndromes associated with hyperfunction of the posterior pituitary and hypothalamus are inappropriate release of ADH and precocious puberty.
INAPPROPRIATE RELEASE OF ADH.
It results in its excessive secretion which manifests clinically by passage of concentrated urine due to increased reabsorption of water and loss of sodium in the urine, consequent hyponatremia, haemodilution, and expansion of intra and extracellular fluid volume.
Inappropriate release of ADH occurs most often in paraneoplastic syndrome e.g. in oat cell carcinoma of the lung, carcinoma of the pancreas, lymphoma, and thymoma.
Infrequently, lesions of the hypothalamus such as trauma, hemorrhage, and meningitis may produce ADH hypersecretion. Rarely, pulmonary diseases such as tuberculosis, lung abscess, pneumoconiosis, empyema, and pneumonia may cause overproduction of ADH.
A tumor in the region of the hypothalamus or the pineal gland may result in the premature release of gonadotropins causing the onset of pubertal changes prior to the age of 9 years. The features include premature development of genitalia both in the male and in the female, growth of pubic hair, and axillary hair. In the female, there is breast growth and the onset of menstruation.