Gigantism and acromegaly are distinct endocrine disorders resulting from the overproduction of Growth Hormone (GH) and the subsequent increase in Insulin-like Growth Factor-1 (IGF-1). The fundamental difference between the two conditions is the patient’s age and the status of their skeletal growth plates when the hormone excess begins. This timing of onset dictates the physical manifestations and long-term consequences of each condition.
Gigantism: Growth Before Plate Closure
Gigantism occurs when the body produces an excessive amount of Growth Hormone during childhood or adolescence, before the growth plates of the long bones have fused. These growth plates (epiphyseal plates) are areas of cartilage at the ends of long bones that allow for longitudinal bone growth. Since these plates remain open, the excess GH stimulates continuous bone production, resulting in a rapid and proportional increase in height.
The primary manifestation of gigantism is an abnormally tall stature, defined as a height significantly above the norm for their age and sex. Children experience accelerated growth velocity, leading to unusually long arms and legs. Although the growth is generalized, the hands and feet can become very large, and facial features may coarsen. Delayed puberty and muscle weakness are also frequently observed symptoms.
Acromegaly: Growth After Plate Closure
Acromegaly develops when Growth Hormone hypersecretion begins in adulthood, after the long bones’ epiphyseal plates have fused. Once the growth plates are closed, the bones can no longer lengthen, preventing an increase in height. Instead, the excess GH and IGF-1 promote the thickening and enlargement of bones, cartilage, and soft tissues in specific areas of the body.
The physical changes in acromegaly are disproportionate and develop slowly, often leading to a diagnostic delay of several years. Patients frequently notice an increase in ring or shoe size, indicating the enlargement of the hands and feet. Coarsened facial features are characteristic, including a protruding lower jaw (prognathism), an enlarged nose and lips, and spacing between the teeth. Other common symptoms include thick and oily skin, excessive sweating (hyperhidrosis), joint pain, and the enlargement of internal organs, such as the heart (cardiomegaly).
The Underlying Cause
Despite the difference in manifestation, gigantism and acromegaly share the same primary cause: the unregulated overproduction of Growth Hormone. In over 95% of cases, this excessive GH secretion is traced to a benign tumor in the pituitary gland, known as a pituitary adenoma. The pituitary gland is a small structure at the base of the brain that regulates many body functions through hormone secretion.
The adenoma develops from somatotroph cells, which are responsible for producing GH. The tumor overrides the body’s natural regulatory mechanisms, leading to the continuous, uncontrolled release of Growth Hormone. This excess GH stimulates the liver to produce high levels of Insulin-like Growth Factor-1 (IGF-1). While a pituitary adenoma is the most common cause, a small number of cases may be due to tumors elsewhere in the body that produce GH or Growth Hormone-Releasing Hormone (GHRH).
Management and Prognosis
Diagnosis for both conditions begins with measuring the levels of IGF-1 in the blood, which are significantly elevated due to the excess Growth Hormone. A subsequent diagnostic test is the oral glucose tolerance test, where a lack of GH suppression after consuming a glucose solution confirms the diagnosis. Once the hormonal imbalance is confirmed, a magnetic resonance imaging (MRI) scan is performed to locate and determine the size of the pituitary adenoma.
The preferred first-line treatment for both gigantism and acromegaly is the surgical removal of the tumor, typically through transsphenoidal surgery. If surgery is not curative or feasible, medical therapies are used to manage the hormone levels. These include somatostatin analogs (such as octreotide or lanreotide), which suppress GH secretion, and GH receptor antagonists, which block the hormone’s action on tissues.
Radiation therapy, often stereotactic radiosurgery, may be utilized for residual tumor tissue that does not respond to surgery or medication. Early diagnosis and effective treatment are important, particularly in gigantism, as controlling GH levels prevents severe complications and maximizes the patient’s quality of life. Untreated hypersecretion of GH in either condition can lead to serious health issues, including cardiovascular disease, diabetes, and sleep apnea.