Gigantism and acromegaly are two rare conditions that arise from the same underlying hormonal imbalance: an excessive production of growth hormone (GH). The pituitary gland, a small structure at the base of the brain, normally releases GH, which stimulates growth and metabolism. When this gland produces too much of this hormone, it triggers a cascade of effects, primarily through the intermediary hormone Insulin-like Growth Factor 1 (IGF-1), leading to abnormal growth patterns. The fundamental distinction between gigantism and acromegaly is the timing of this GH excess relative to a person’s skeletal maturity.
The Core Distinction: Age of Onset
The primary difference between these two conditions is determined by the status of the epiphyseal plates, commonly known as growth plates, within the long bones. Gigantism occurs when excessive GH secretion begins in childhood or adolescence, before these plates have fused. Growth plates are areas of cartilage near the ends of long bones that allow for linear growth.
Because the plates remain open in children, high levels of GH and IGF-1 stimulate rapid and excessive elongation of the bones, resulting in abnormally tall stature and proportional growth. Acromegaly develops when the overproduction of GH begins in adulthood, after the epiphyseal plates have naturally fused into solid bone. Once the growth plates are closed, the bones can no longer grow in length. Instead, the persistent GH and IGF-1 excess causes bones and soft tissues to thicken and enlarge laterally.
Clinical Presentation of Gigantism
The defining characteristic of gigantism is an accelerated rate of linear growth, resulting in a height significantly above average for the child’s age and gender. This excessive growth is generally proportional, meaning the limbs and trunk maintain a reasonable balance.
Children with gigantism often develop features related to the overgrowth of soft tissues and bone structures, such as enlarged hands and feet, coarse facial features, and a prominent jaw. Other symptoms can include headaches and visual disturbances caused by the pituitary tumor pressing on nearby structures, a delay in the onset of puberty, and general muscle weakness and fatigue.
Clinical Presentation of Acromegaly
Acromegaly occurs after the skeleton has matured and linear growth has ceased. The excessive GH and IGF-1 instead stimulate the proliferation and thickening of connective tissue, bone, and cartilage. This leads to a gradual, insidious enlargement of the acral parts of the body—the hands, feet, and face. Patients typically notice an increase in ring or shoe size as one of the earliest signs. Facial changes become pronounced over time, including a broadening of the nose, thickening of the lips, and the development of a prominent brow ridge (frontal bossing). The lower jaw often protrudes excessively (prognathism), which can cause dental spacing issues.
Soft tissues throughout the body are also hypertrophied. This can lead to carpal tunnel syndrome due to nerve compression in the wrist and visceromegaly, which is the enlargement of internal organs, particularly the heart and kidneys. Acromegaly is associated with metabolic complications, such as insulin resistance and an increased risk of developing type 2 diabetes and cardiovascular disease.
Underlying Causes and Management
For both gigantism and acromegaly, the cause is overwhelmingly the same: a benign tumor of the pituitary gland, known as a pituitary adenoma. These tumors secrete growth hormone autonomously, leading to the hormonal excess. In over 95% of cases, this pituitary adenoma is the source of the high GH levels, though rare genetic syndromes like McCune-Albright Syndrome or X-linked acrogigantism can be responsible.
The management strategy focuses on lowering the levels of GH and IGF-1 and addressing the tumor itself. The preferred treatment is usually transsphenoidal surgery, where the tumor is removed through the nasal cavity, offering a high chance of cure if the tumor is small. If surgery is unsuccessful or only partially effective, medical therapy is employed.
Medications include somatostatin analogs, which block the release of GH from the tumor, and GH receptor antagonists, which prevent the hormone from acting on target cells. Radiation therapy is reserved as a tertiary treatment for patients who have residual disease after surgery. While the treatment modalities are similar, the management goals differ: in gigantism, the priority is stopping the excessive linear growth, whereas in acromegaly, the focus is on halting disease progression and managing the associated long-term health complications.