Hypopituitarism is the decreased (hypo) secretion of one or more of the eight hormones normally produced by the pituitary gland at the base of the brain.If there is decreased secretion of one specific pituitary hormone, the condition is known as selective hypopituitarism. If there is decreased secretion of most or all pituitary hormones, the term panhypopituitarism is used.

Hypopituitarism is a complex medical condition associated with increased morbidity and mortality, requires complicated treatment regimens, and necessitates lifelong follow up by the endocrinologist.

Aetiology

Of the various causes of hypopituitarism in adults (see box), pituitary adenoma or its treatment by surgery and/or radiotherapy is by far the commonest. Macroadenomas (greater than 1 cm) are associated with one or more trophic hormone deficits in 30% of cases direct compression and destruction of the surrounding normal pituitary leads to hyposecretion. Other postulated mechanisms include primary mass effect of the tumour on the vascular portal system/pituitary stalk, raised intrasellar pressure affecting portal circulation, and focal pituitary necrosis secondary to prolonged interruption of portal blood supply. While microadenomas (less than 1 cm) rarely affect pituitary function, prolactin producing microadenomas often present with hypogonadism because of the suppressive action of a high prolactin (PRL) level on gonadotrophins' (follicle stimulating hormone FSH and luteinising hormone LH) secretion. Among the peripituitary tumours causing central endocrine dysfunction, craniopharyngioma is the commonest.

Occurrence of hypopituitarism after pituitary surgery is influenced by tumour size, extent of invasion into surrounding structures, remaining viable normal pituitary, and the skill of the neurosurgeon. Transient postoperative diabetes insipidus (DI) is seen in 5% of cases but permanent DI occurs less frequently. At least partial recovery of pituitary function in 40%–65% of patients has been reported after surgery but postoperative deterioration has also been reported.Patients should be made aware of the possibility of hypopituitarism before surgery. Post‐surgical endocrine assessment is mandatory.

Anterior hypopituitarism may follow cranial radiotherapy used in treating various intracranial tumours, acute lymphoblastic leukaemia (prophylactic cranial radiotherapy), and those receiving total body irradiation. The impact is dependent on the total dose, fractionation, duration of treatment, and time elapsed since radiation exposure to the hypothalamic‐pituitary axis.In one series after a radiotherapy dose to the hypothalamic‐pituitary axis of 37.5 to 42.5 Gy, after five years all patients were growth hormone (GH) deficient, 90% gonadotrophin deficient, 77

On the basis of the GH response to ARG+GHRH, 41 patients had very severe GHD (GH peak, 0.9 ± 0.08 μg/L; group 1), 25 patients had severe GHD (GH peak, 4.7 ± 0.4 μg/L; group 2), 18 patients had partial GHD (GH peak, 11.0 ± 0.3 μg/L; group 3), and 17 patients had normal GH responses (GH peak, 28.3 ± 4.3 μg/L; group 4). In the 35 controls (group 5), the GH response after ARG+GHRH was 40.7 ± 2.2 μg/L.

Plasma IGF-I concentrations in patients in groups 1 (76.5 ± 7.6μ g/L) and 2 (80.3 ± 7.5 μg/L) were similar and lower (P < 0>P< 0>P < 0>

Management of hypopituitarism

The treatment of hypopituitarism includes therapies directed at the underlying disease process, and endocrine replacement therapy. The pituitary tumours may be treated with medical therapy, surgery, radiotherapy, or a combination of these modalities. A macroprolactinoma, for instance, is amenable to treatment with dopamine agonists, there is a high surgical cure rate for GH secreting microadenoma by skilled surgeons.

Hormone Replacement Therapy

The goals of HRT in hypopituitarism are to achieve normal levels of the circulating hormones, to restore normal physiology as closely as possible, and to avoid the symptoms of deficiency with minimal side effects.

GHD in adults is associated with increased fat mass, reduced lean mass, osteopenia, impaired fibrinolysis, altered cardiac structure and function, unfavorable glucose and lipid metabolism, reduced exercise capacity, and reduced quality of life (3, 13, 14). Reduced BMD has been widely reported in hypo pituitary patients (3, 4–8), although the roles of individual pituitary hormone deficiency and/or of replacement therapy in the development of bone loss have not been firmly elucidated.

Conclusion

Hypopituitarism is associated with increased mortality and morbidity, necessitates complicated treatment regimens, and significantly affects the economy of the healthcare system. Strategies to limit the use of conventional radiotherapy may well lead to a reduced incidence of hypopitutarism. It is probable that hormonal treatment that approaches normal physiology might have a favourable influence on the adverse outcomes; therefore optimising replacement and lifelong follow up is appropriate.