Nelson's syndrome is the rapid enlargement of a pituitary adenoma

Pituitary adenoma

Pituitary adenomas are tumors that occur in the pituitary gland, and account for about 15% of intracranial neoplasms. Tumors which exceed 10 mm in size are defined as macroadenomas, and those smaller than 10 mm are referred to as microadenomas...

 that occurs after the removal of both adrenal gland

Adrenal gland

In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...

s.

Pathophysiology

Removal of both adrenal glands, or bilateral adrenalectomy

Adrenalectomy

Adrenalectomy is the surgical removal of one or both adrenal glands. It is usually advised for patients with tumors of the adrenal glands. The procedure can be performed using an open incision or laparoscopic technique....

, is an operation

Surgery

Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 for Cushing's syndrome

Cushing's syndrome

Cushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone or CRH...

. Removal of both adrenals eliminates production of cortisol

Cortisol

Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

, and the lack of cortisol's negative feedback

Negative feedback

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

 can allow any preexisting pituitary adenoma to grow unchecked. Continued growth can cause mass effect

Mass effect (medicine)

In medicine, a mass effect is the effect of a growing mass , for example the consequences of a growing cancer....

s due to physical compression of brain tissue, along with increased production of adrenocorticotrophic hormone (ACTH) and melanocyte stimulating hormone (MSH).

Presentation

The common signs

Signs

Signs is the plural of sign. See sign .Signs may also refer to:*Signs , a 2002 film by M. Night Shyamalan*Signs , a journal of women's studies...

 and symptoms include muscle weakness

Muscle weakness

Muscle weakness or myasthenia is a lack of muscle strength. The causes are many and can be divided into conditions that have true or perceived muscle weakness...

 and skin hyperpigmentation

Hyperpigmentation

In dermatology, hyperpigmentation is the darkening of an area of skin or nails caused by increased melanin.-Causes:Hyperpigmentation may be caused by sun damage, inflammation, or other skin injuries, including those related to acne vulgaris...

due to excess MSH. Nelson's syndrome is now rare because bilateral adrenalectomy is now only used in extreme circumstances.

Treatment

Pituitary surgery is performed in some cases.
The risk can also be minimized by pituitary irradiation.

History

The condition is named for the American endocrinologist Dr Don Nelson, who first reported on the phenomenon in 1960.