Nelson syndrome is a medical disorder which is characterized by abnormal secretion of hormones and enlargement of the pituitary gland. This condition occurs after an adrenalectomy, which causes the growth of a pituitary tumor. This is a rare disorder, thus doing research on it is a great challenge. Before the 1980's, 20-40% of patients with a pituitary adenoma who under went bilateral adrenalectomy, developed Nelson syndrome within 1-4 years (UCLA, 25 Jul 2003). Reports have shown a steady decline in cases of Nelson syndrome since the 1980's and this has been credited to the better assessment and management of patients with Cushing's disease (Chrousos, 25 Jul 2003). .
Studies have proven that more than 99% of all cases relating to Nelson Syndrome arise after a patient has had a bilateral adrenalectomy done for Cushing Disease (Chrousos, 25 Jul 2003). The single most common cause of the developing tumor with high levels of adrenocorticotropin or ACTH is primary adrenal insufficiency and this can either be congenital or acquired (Chrousos, 25 Jul 2003). The congenital cause includes hypoplasia or adrenal hyperplasia (Chrousos, 25 Jul 2003). The acquired cases of adrenal insufficiency include Addison disease and adrenoleukodystrophy (Chrousos, 25 Jul 2003).
Nelson syndrome primarily affects younger individuals and women (Chrousos, 25 March 2003). It affects people of all races equally and is not confined to a certain geographic location. Pregnancy and young age increase the risk factors for acquiring this disease. Mortality from Nelson syndrome occurs from local tumor extension or invasion. Patients become deeply pigmented and in rare cases and malignant formation of ACTH or adrenocorticotropin start secreting Nelson tumors (Chrousos, 25 Jul 2003). Death may occur due to loss of pituitary function which may result from compression or replacement of normal pituitary tissue by the tumor.