INTRODUCTION

Pituitary gigantism refers to growth hormone (GH) excess that occurs before fusion of the epiphyseal growth plates. Therefore, by definition the condition is only seen in growing children. In this setting, elevated levels of serum GH and IGF-I cause rapid, excessive linear growth and, if unchecked, extremely tall adult stature. In contrast, GH excess that begins in adulthood, after complete epiphyseal fusion, has no effect on stature and is called acromegaly. Although many historical claims of gigantism have been exaggerated, case reports of true pituitary giants with heights of up to 8 feet 11 inches (272 cm) are documented in the medical literature [1]. (See "Causes and clinical manifestations of acromegaly".)

EPIDEMIOLOGY

Pituitary gigantism is a rare disorder. Most pediatric endocrinologists may see at most one or two patients with the condition during their careers. In one large series of 2367 children and adolescents with pituitary adenomas, only 15 (0.6 percent) had pituitary gigantism [2]. Much of our understanding of this disease is derived from isolated case reports and extrapolation from the adult literature [3]. No sex predilection is known. Gigantism may occur at any age, and has been observed as early as the first six to nine months of age.

ASSOCIATED CONDITIONS

Pituitary gigantism typically is a sporadic and isolated condition. However, it may occur within the context of a coexisting disorder or arise according to a pattern of familial inheritance.

Syndromes in which gigantism is a well-recognized feature include McCune Albright Syndrome (MAS), multiple endocrine neoplasia type I (MEN1), and Carney complex. The frequency of gigantism seen in these conditions varies:

• Approximately 20 percent of patients with MAS are thought to have GH hypersecretion [4,5], although few large case series are available [6]. Subclinical GH excess also has been reported in MAS, where it results in unexpected normal (rather than short) stature in the setting of untreated precocious puberty [7]. (See "Definition, etiology, and evaluation of precocious puberty", section on 'Causes of gonadotropin independent precocious puberty (GIPP)'.)
• GH excess eventually develops in up to 60 percent of patients affected with MEN1, usually with onset in the fourth and fifth decades of life [8,9]. GH excess in MEN1 is extremely rare in individuals younger than 40 years, although it has been reported in a child as young as age five years [10]. (See "Clinical manifestations and diagnosis of multiple endocrine neoplasia type 1".)
• GH-secreting pituitary tumors are reported in approximately 15 percent of cases of the Carney complex, and typically begin during the third and fourth decades of life [11,12]. (See "Cushing's syndrome due to primary pigmented nodular adrenocortical disease", section on 'Carney complex (CNC)'.)
• Gigantism also has been observed infrequently in the setting of neurofibromatosis and optic nerve tumors [13-15]. (See "Neurofibromatosis type 1 (von Recklinghausen's disease)".)
• Multiple kindreds have been identified in whom isolated GH excess is transmitted in an autosomal dominant fashion, resulting in an entity known as isolated familial somatotrophinomas. Affected individuals in these families have been as young as nine years of age at diagnosis [16].