Acromegaly And Gigantism
Chronic, progressive diseases, acromegaly and gigantism are marked by hormonal dysfunction and startling skeletal overgrowth. Acromegaly occurs after epiphyseal closure, causing bone thickening and transverse growth and visceromegaly. Gigantism begins before epiphyseal closure and causes proportional overgrowth of all body tissues. Although the prognosis depends on the causative factor, these disorders usually reduce life expectancy unless treated in a timely way.
Typically, oversecretion of human growth hormone (HGH) produces changes throughout the entire body, resulting in acromegaly and, when oversecretion occurs before puberty, gigantism. Eosinophilic or mixed-cell adenomas of the anterior pituitary gland may cause this oversecretion, but the cause of the tumors themselves remains unclear. Rarely, HGH levels are elevated in more than one family member, which suggests the possibility of a genetic cause.
The earliest clinical sign of acromegaly is soft tissue swelling of the extremities, which causes coarsening of the facial features. This rare form of hyperpituitarism occurs equally among men and women, usually between ages 30 and 50.
In gigantism, proportional overgrowth of all body tissues starts before epiphyseal closure. This causes remarkable height increases of as much as 6" (15 cm) a year. Gigantism affects infants and children, causing them to attain as much as three times the normal height for their age. As adults, they may ultimately reach a height of more than 80" (203 cm).
Signs and symptoms
Acromegaly develops slowly, whereas gigantism develops abruptly.
Acromegaly :- Acromegaly typically produces diaphoresis, oily skin, hypermetabolism, and hypertrichosis. Severe headache, central nervous system impairment, bitemporal hemianopia, loss of visual acuity, and blindness may result from the intrasellar tumor compressing the optic chiasm or nerves.
Hypersecretion of HGH produces cartilaginous and connective tissue overgrowth, resulting in a characteristic hulking appearance, with an enlarged supraorbital ridge and thickened ears and nose. Prognathism, projection of the jaw, becomes marked and may interfere with chewing. Laryngeal hypertrophy, paranasal sinus enlargement, and thickening of the tongue cause the voice to sound deep and hollow. Distal phalanges display an arrowhead appearance on Xrays, and the fingers are thickened. Irritability, hostility, and various psychological disturbances may occur.
Prolonged effects of excessive HGH secretion include bowlegs, barrel chest, arthritis, osteoporosis, kyphosis, hypertension, and arteriosclerosis. Both gigantism and acromegaly may also cause signs of glucose intolerance and clinically apparent diabetes mellitus because of the insulin-antagonistic character of HGH.
Gigantism produces some of the same skeletal abnormalities seen in acromegaly. As the disease progresses, the pituitary tumor enlarges and invades normal tissue, resulting in the loss of other trophic hormones, such as thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, and corticotropin, thus causing the target organ to stop functioning.
Plasma HGH levels measured by radioimmunoassay typically are elevated. However, because HGH secretion is pulsatile, the results of random sampling may be misleading. IGF-I (somatomedin-C) levels offer a better screening alternative.
The glucose suppression test offers more reliable information. Glucose normally suppresses HGH secretion; therefore, a glucose infusion that doesn't suppress the hormone level to below the accepted normal value of 2 ng/ml, when combined with characteristic clinical features, strongly suggests hyperpituitarism.
In addition, skull X-rays, a computed tomography scan, arteriography, and magnetic resonance imaging determine the presence and extent of the pituitary lesion. Bone X-rays showing a thickening of the cranium (especially of frontal, occipital, and parietal bones) and of the long bones as well as osteoarthritis in the spine support this diagnosis.
Overproduction of HGH is curbed through removal of the underlying tumor by cranial or transsphenoidal hypophysectomy or pituitary radiation therapy. In acromegaly, surgery is mandatory when a tumor causes blindness or other severe neurologic disturbances.
Postoperative therapy often requires replacement of thyroid and gonadal hormones and cortisone. Adjunctive treatment may include administration of bromocriptine and octreotide, which inhibit HGH synthesis.
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