Classification of Hyperpituitarism and Pathogenetic Mechanisms
Globally, hyperpituitarism is divided into partial and total. Total hyperpituitarism is extremely rare and its existence remains debatable. Partial hyperpituitarism encompasses a spectrum of endocrine disorders:
- Pituitary gigantism.
- Acromegaly.
- Hyperprolactinemia.
- Hypermelanotropinemia.
- Pituitary (true) precocious puberty syndrome.
- Pituitary hyperthyroidism.
- Pituitary hypercortisolism (Cushing's disease).
The development of gigantism and acromegaly involves disruptions at various levels of regulation. Three key pathogenetic mechanisms (initiating links) are distinguished:
- Centrogenic mechanism. Results from damage to the neurons of the cerebral cortex and/or hypothalamus. This leads to massive hyperproduction of growth hormone-releasing hormone (GHRH) and growth hormone (GH) itself. In some cases, the triggering factor is a decrease in the normal production of somatostatin, which normally inhibits GH secretion.
- Primary glandular (pituitary) mechanism. A direct consequence of increased GH synthesis directly by acidophilic cells of the adenohypophysis.
- Post-glandular (receptor) mechanism. In this case, hormone levels may not be critically elevated, but there is an increased hyperaffinity (pathological affinity) of target tissue and organ receptors for GH molecules.
Clinical Manifestations of Gigantism
Gigantism is characterized by large-scale systemic alterations affecting both appearance and internal organ systems.
Skeletal and Organ Changes The leading symptom is height growth exceeding physiological norms (more than 200 cm in males and 190 cm in females). This is based on accelerated epiphyseal and periosteal growth of tubular bones. There is often a mismatch between internal organ size and body parameters. As a rule, splanchnomegaly (enlargement of organs) develops, though in rare cases internal organs may relatively lag in growth. In both scenarios, this leads to functional insufficiency of organs such as the heart or liver, as their capacity cannot meet the increased demands of a massive body.
Muscular and Reproductive Systems Muscle development is disproportionate. Early in the disease, muscle mass volume still corresponds to overall body dimensions. However, as the disease progresses, muscle growth critically lags behind. Degenerative changes develop in myofibrils, and muscle tissue is replaced by connective tissue, clinically manifesting as hypotonia, hypotrophy, and marked muscle weakness. Concurrently, hypogenitalism (underdevelopment of internal and external genitalia) develops due to insufficient synthesis or effects of gonadotropins.
Metabolism and Mental Status Since GH is a potent counter-regulatory hormone, patients predictably experience impaired carbohydrate metabolism: hyperglycemia is recorded, and diabetes mellitus frequently manifests. The psychological status of patients is characterized by emotional instability, irritability, sleep disturbances, asthenia, and decreased cognitive performance. This is related to the dysfunction of cortical and subcortical neurons, the stress response to a severe chronic illness, and concomitant hyperthyroidism.
Specifics of the Clinical Presentation of Acromegaly
While gigantism occurs during active growth, acromegaly has its own specific course associated with the effects of excess GH on an already fully formed organism.
Musculoskeletal System and Soft Tissues Characterized by enlargement of the hands and feet due to somatotropin-stimulated periosteal bone growth. Soft tissues thicken, the skin coarsens, and facial features become coarse. Macroglossia (enlargement of the tongue) and splanchnomegaly are observed. These changes result from excessive proliferation of connective tissue and parenchymal elements directly influenced by GH.
Neurological and Psychological Symptoms Due to bone thickening and soft tissue hypertrophy, bone canals and depressions narrow. This leads to compression of passing nerve trunks. Clinically, this manifests as paresthesias, particularly acroparesthesias (marked discomfort, numbness, and tingling in the hands and feet). Various psychological disorders are also recorded.
Metabolism and Reproductive Function
- Carbohydrate metabolism: persistent hyperglycemia is noted in more than 50% of patients, and one in ten develops overt diabetes mellitus.
- Lipid metabolism: blood concentrations of cholesterol, lecithin, free fatty acids (FFAs), ketone bodies, and lipoproteins increase.
- Reproductive sphere: excessive GH effects provoke decreased libido, impotence, and in women, dysmenorrhea and galactorrhea.