PITUITARY DISORDERS

Pituitary (hypophysis) is a vital link in neuro-endocrinal system, consisting of two embryologically and func­tionally separate parts-anterior pituitary and posterior pituitary (neurohypophysis).

Anterior pituitary is derived from Rathke's pouch as an invagination of oral ectoderm and secretes seven different hormones (Table 22.2), which either regulate other endocrine glands or act directly on target organs, e.g. breast, melanocytes and gonads. Of these, MSH is structurally a part of ACTH (first 13 amino acids, no corticotrophin activity), and currently, ACTH, rather than MSH, is considered as the regulator of melanocyte function and pigmentation.

TABLE 22.2: Pituitary hormones

TABLE 22.3: Causes of hypopituitarism

Anterior pituitary (synthesis and release)

• Growth hormone (GH)

• Thyroid stimulating hormone (TSH)

• Adrenocorticotropic hormone (ACTH)

• Follicle stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Prolactin (PRL)

• Melanocyte stimulating hormone (MSH)[§§§§§§] [*******]

Posterior pituitary (storage and release)

• Oxytocin

• Vasopressin or ADH

*Seetext

Posterior pituitary is connected with hypothalamus via nerve fibers and stores primary hormones synthesized in hypothalamus, i.e. oxytocin and vasopressin. Release of these hormones is mainly regulated by higher neurological centers and changes in body homeostasis.

22.2.1 HYPOPITUITARISM___________________________

Hypopituitarism may be limited to single hormonal deficiency (commonest-Isolated GH deficiency) or involves multiple pituitary hormone deficiency (MPHD) Etiology: Hypopituitarism may be congenital or acquired (Table 22.3). Apart from primary pituitary lesions, similar abnormalities are also caused by deficiency of corresponding releasing factor due to hypothalamic lesions or end-organ resistance despite normal hormonal levels.

Clinical manifestations of hypopituitarism depend on the spectrum of hormonal deficiencies and the age of onset.

• Congenital hypopituitarism may present at birth with micropenis or hypoplastic labia minora, hypoglycemia or prolonged jaundice or subsequently with—(a) short stature with lower growth velocity and delayed bone age, (b) facial dysmorphism with frontal prominence, saddle nose, prominent eyes, midfacial hypoplasia, small hands and feet and delayed dentition, and (c) absent/delayed sexual maturation. Intelligence is usually normal.

• Acquired hypopituitarism presents at any age with arrested physical growth and sexual maturation, as well as features of multiple endocrine deficiencies (hypothyroidism, hypoadrenalism) and causative intracranial lesions (e.g. raised intracranial pressure, localizing signs).

Diagnosis depends on pituitary/target endocrinal hor­mone assays, response to hypothalamic hormones, e.g. failed GH stimulation test, low Free T4 and TSH and low cortisol and ACTH levels as well as radioimaging studies for intracranial lesions.

Treatment includes management of primary causes, e.g. tumor, as well as hormone replacement therapy,

a. Developmental defects (Pituitary a-#8725;hypoplasia)

- With/without CNS abnormalities

- Due to hypothalamic defects

- Empty sella syndrome

b. Genetic hormonal synthesis defects

- Isolated growth hormone (GH) deficiency

- Multiple hormonal deficiencies

c. Destructive lesions (acquired)

- Tumors: Craniopharyngioma

- Trauma: Basal fractures, surgery, radiation

- Hypoxic/vascular injuries

- Infiltrative: Histiocytosis

d. End-organ resistance

- GH receptor defects (Laron dwarfism)

- Insulin-like growth factor (IGF) deficiency

depending on the needs. Treatment of GH deficiency is discussed in next section.

22.2.2