[Endocrine consequences of hemochromatosis]

Insights into non-classic and emerging causes of hypopituitarism

Hypopituitarism is defined as one or more partial or complete pituitary hormone deficiencies, which are related to the anterior and/or posterior gland and can have an onset in childhood or adulthood. The most common aetiology is a sellar or suprasellar lesion, often an adenoma, which causes hypopituitarism due to tumour mass effects, or the effects of surgery and/or radiation therapy. However, other clinical conditions, such as traumatic brain injury, and autoimmune and inflammatory diseases, can result in hypopituitarism, and there are also genetic causes of hypopituitarism. Furthermore, the use of immune checkpoint inhibitors to treat cancer is increasing the risk of hypopituitarism, with a pattern of hormone defects that is different from the classic patterns and depends on mechanisms that are specific for each drug. Moreover, autoantibody production against the pituitary and hypothalamus has been demonstrated in studies investigating the development or worsening of some cases of hypopituitarism. Finally, evidence suggests that posterior pituitary damage can affect oxytocin secretion. The aim of this Review is to summarize current knowledge on non-classic and emerging causes of hypopituitarism, so as to help clinicians improve early identification, avoid life-threatening events and improve the clinical care and quality of life of patients at risk of hypopituitarism.

DIAGNOSIS OF ENDOCRINE DISEASE: Expanding the cause of hypopituitarism

Hypopituitarism is defined as one or more pituitary hormone deficits due to a lesion in the hypothalamic-pituitary region. By far, the most common cause of hypopituitarism associated with a sellar mass is a pituitary adenoma. A high index of suspicion is required for diagnosing hypopituitarism in several other conditions such as other massess in the sellar and parasellar region, brain damage caused by radiation and by traumatic brain injury, vascular lesions, infiltrative/immunological/inflammatory diseases (lymphocytic hypophysitis, sarcoidosis and hemochromatosis), infectious diseases and genetic disorders. Hypopituitarism may be permanent and progressive with sequential pattern of hormone deficiencies (radiation-induced hypopituitarism) or transient after traumatic brain injury with possible recovery occurring years from the initial event. In recent years, there is increased reporting of less common and less reported causes of hypopituitarism with its delayed diagnosis. The aim of this review is to summarize the published data and to allow earlier identification of populations at risk of hypopituitarism as optimal hormonal replacement may significantly improve their quality of life and life expectancy.

The causes of hypopituitarism in the absence of abnormal pituitary imaging

BACKGROUND

Hypopituitarism in the absence of a history of pituitary pathology or abnormal pituitary imaging is rare.

AIM

To identify the cause of hypopituitarism in individuals in whom pituitary imaging was normal.

DESIGN

Retrospective analysis of electronic patient record.

METHOD

A review of the pituitary function in the 506 patients on the Morriston Hospital pituitary database revealed 230 had some degree of hypopituitarism and of these, 21 (9%) had normal pituitary imaging.

RESULTS

Of this group, six patients had a past medical history of subarachnoid haemorrhage, head injury or meningitis, and mainly suffered from a deficiency of antidiuretic hormone. One patient had a stroke resulting in multiple anterior hormone deficiencies and six individuals had idiopathic cranial diabetes insipidus (DI). Subsequent investigations of the remaining eight patients with normal pituitary imaging revealed that two had neurosarcoidosis both of whom had panhypopituitarism. Four patients had haemochromatosis which resulted in gonadotropin deficiency in two, DI in one and panhypopituitarism in the other. There were two individuals with confirmed hypopituitarism and multiple hormone deficiencies in which no cause could be identified.

CONCLUSION

These results show that hypopituitarism in the absence of pituitary pathology or an identifiable cause is rare. In patients with multiple anterior pituitary hormone deficiencies haemochromatosis and sarcoidosis should be considered.

Approach to the male patient with congenital hypogonadotropic hypogonadism

The term "congenital hypogonadotropic hypogonadism" (CHH) refers to a group of disorders featuring complete or partial pubertal failure due to insufficient secretion of the pituitary gonadotropins LH and FSH. Many boys (or their parents) will seek medical consultation because of partial or absent virilization after 14 yr of age. Small testes are very frequent, but height is generally normal. Laboratory diagnosis of hypogonadotropic hypogonadism is relatively simple, with very low circulating total testosterone and low to low-normal gonadotropin and inhibin B levels. This hormone profile rules out a primary testicular disorder. Before diagnosing CHH, however, it is necessary to rule out a pituitary tumor or pituitary infiltration by imaging studies, juvenile hemochromatosis, and a systemic disorder that, by undermining nutritional status, could affect gonadotropin secretion and pubertal development. Anterior pituitary function must be thoroughly investigated to rule out a more complex endocrine disorder with multiple hormone deficiencies and thus to conclude that the hypogonadotropic hypogonadism is isolated. The most likely differential diagnosis before age 18 yr is constitutional delay of puberty. Apart from non-Kallmann syndromic forms, which are often diagnosed during childhood, the two main forms of CHH seen by endocrinologists are Kallmann syndrome, in which CHH is associated with impaired sense of smell, and isolated CHH with normal olfaction. Anosmia can be easily diagnosed by questioning the patient, whereas olfactometry is necessary to determine reliably whether olfaction is normal or partially defective. This step is important before embarking on a search for genetic mutations, which will also be useful for genetic counseling. The choice of a particular hormone replacement therapy protocol aimed at virilizing the patient will depend on age at diagnosis and local practices.

Non-syndromic congenital hypogonadotropic hypogonadism: clinical presentation and genotype-phenotype relationships

Congenital hypogonadotropic hypogonadism (CHH) results from abnormal gonadotropin secretion, and it is characterized by impaired pubertal development. CHH is caused by defective GNRH release, or by a gonadotrope cell dysfunction in the pituitary. Identification of genetic abnormalities related to CHH has provided major insights into the pathways critical for the development, maturation, and function of the reproductive axis. Mutations in five genes have been found specifically in Kallmann's syndrome, a disorder in which CHH is related to abnormal GNRH neuron ontogenesis and is associated with anosmia or hyposmia. In combined pituitary hormone deficiency or in complex syndromic CHH in which gonadotropin deficiency is either incidental or only one aspect of a more complex endocrine disorder or a non-endocrine disorder, other mutations affecting GNRH and/or gonadotropin secretion have been reported. Often, the CHH phenotype is tightly linked to an isolated deficiency of gonadotropin secretion. These patients, who have no associated signs or hormone deficiencies independent of the deficiency in gonadotropin and sex steroids, have isolated CHH. In some familial cases, they are due to genetic alterations affecting GNRH secretion (mutations in GNRH1, GPR54/KISS1R and TAC3 and TACR3) or the GNRH sensitivity of the gonadotropic cells (GNRHR). A minority of patients with Kallmann's syndrome or a syndromic form of CHH may also appear to have isolated CHH, but close clinical, familial, and genetic studies can reorient the diagnosis, which is important for genetic counseling in the context of assisted reproductive medicine. This review focuses on published cases of isolated CHH, its clinical and endocrine features, genetic causes, and genotype-phenotype relationships.