Sellarsuprasellar tumours pituitary adenoma

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2. HYPOSECRETION

Many pituitary tumours are diagnosed before panhypopituitarism develops, but large tumours may cause gradual impairment of pituitary hormone secretion. Growth hormone and the gonadotrophins are first affected, followed by TSH and ACTH. Panhypopituitarism only occurs when more than 80% of the anterior pituitary is destroyed.

Impaired secretion

Adults

Gonadotrophins -ACTH-

TSH -Prolactin* -

'Adult GH deficiency syndrome' -weight gain, loss of libido, fatigue Amenorrhoea, sterility, loss of libido Glucocorticoid and androgen deficiency, muscle weakness and fatigue Secondary hypothyroidism -sensitivity to cold, dry skin, physical and mental sluggishness, coarseness of hair Failure of lactation

Pituitary dwarfism -diminished somatic growth, retarded sexual development, hypoglycaemic episodes, normal intelligence

*Prolactin secretion is most resistant to pituitary damage. Deficiency is seldom evident, usually only presenting after postpartum haemorrhage (Sheehan's syndrome) as a failure of lactation associated with the other features of panhypopituitarism.

Pituitary hormone assay cannot distinguish low 'normal' levels from impaired secretion, but low levels of pituitary hormone in the presence of low target gland hormones confirm hyposecretion, e.g. low TSH levels despite a low serum thyroxine. Basal levels guide replacement therapy.

The lack of response to tests designed to increase specific pituitary hormones provides additional confirmation of hypofunction:

Insulin tolerance test: Hypoglycaemia acting via the hypothalamic pituitary axis should elevate GH and ACTH levels, the latter causing a significant rise in plasma Cortisol.

Gonadotrophs releasing hormone (GnRH) injection should produce a rapid rise in LH and a slower rise in FSH. Thyrotropin releasing hormone (TRH) injection should increase plasma levels of both TSH and prolactin.

The above tests can be carried out simultaneously as the Combined pituitary stimulation lest. Insulin, GnRH and TRH are injected intravenously and all anterior pituitary hormones measured from repeated blood samples taken over a 2-hour period. Glucose levels are also checked to ensure adequacy of the hypoglycaemia.

PITUITARY APOPLEXY

This is an uncommon complication of pituitary tumours due to the occurrence of haemorrhage into the tumour substance. Severe headache of sudden onset simulating subarachnoid haemorrhage, rapidly progressive visual failure and extraocular nerve palsies accompany acute pituitary insufficiency. Death may follow unless urgent steroid treatment 330 is instituted.

2. Gonadotrophin -

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