Secondary adrenal insufficiency

Secondary adrenal insufficiency
Name	Secondary adrenal insufficiency
Synonyms	Secondary hypocortisolism, Secondary adrenocortical insufficiency
Field	Endocrinology
Symptoms	Fatigue, weakness, weight loss, low blood pressure
Complications	Adrenal crisis
Causes	Pituitary gland dysfunction, Hypothalamus dysfunction, exogenous glucocorticoid use
Diagnostic method	ACTH stimulation test, Insulin tolerance test, CRH stimulation test
Treatment	Hydrocortisone, Prednisone
Medication	Corticosteroid

Secondary adrenal insufficiency. It is a form of adrenal insufficiency characterized by deficient production of cortisol due to inadequate stimulation of the adrenal glands by adrenocorticotropic hormone (ACTH). This condition results from a problem in the pituitary gland or the hypothalamus, rather than a primary defect in the adrenal cortex itself. It leads to a distinctive hormonal profile and requires specific diagnostic and management strategies distinct from Addison's disease.

Definition and pathophysiology

Secondary adrenal insufficiency is defined by an inadequate cortisol response from the adrenal glands caused by insufficient secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary. The pathophysiology typically involves a lesion or functional impairment at the level of the pituitary gland or the hypothalamus, which disrupts the normal hypothalamic-pituitary-adrenal axis. In this condition, the adrenal cortex itself is generally intact but becomes atrophic from disuse due to the lack of trophic stimulation from ACTH. This contrasts sharply with Addison's disease, where destruction of the adrenal cortex occurs. The renin-angiotensin-aldosterone system remains largely functional, so electrolyte disturbances like hyperkalemia are uncommon.

Causes

The most common cause of secondary adrenal insufficiency is prolonged exogenous glucocorticoid administration, which suppresses the hypothalamic-pituitary-adrenal axis. Other causes involve structural or functional disorders of the pituitary gland or hypothalamus. These include pituitary adenomas, such as non-functioning adenomas or those following treatment for Cushing's disease, craniopharyngioma, metastasis from cancers like breast cancer or lung cancer, and infiltrative diseases like sarcoidosis or hemochromatosis. Additional causes are Sheehan's syndrome, traumatic brain injury, pituitary apoplexy, and genetic conditions affecting pituitary development like mutations in the PROP1 gene. Radiation therapy to the sella turcica for tumors like nasopharyngeal carcinoma is also a recognized cause.

Signs and symptoms

Clinical manifestations are often insidious and non-specific, primarily reflecting glucocorticoid deficiency. Common symptoms include profound fatigue, general weakness, weight loss, anorexia, nausea, and myalgia. Unlike Addison's disease, symptoms of mineralocorticoid deficiency such as salt craving, hyperkalemia, and severe hypotension are typically absent because the renin-angiotensin-aldosterone system is independent of ACTH. Patients may exhibit hypoglycemia, especially in children, and experience symptoms of other concurrent pituitary hormone deficiencies, such as those from lack of thyroid-stimulating hormone or gonadotropins. An adrenal crisis, characterized by vomiting, hypotension, and shock, can be precipitated by stress, infection, or surgery.

Diagnosis

Diagnosis involves assessing the integrity of the hypothalamic-pituitary-adrenal axis. The initial step is often a morning serum cortisol and ACTH level, which typically shows a low cortisol with an inappropriately low or normal ACTH. The definitive test is the ACTH stimulation test (cosyntropin stimulation test); a subnormal cortisol response confirms adrenal insufficiency. To distinguish secondary from primary causes, a prolonged ACTH stimulation test or measurement of plasma ACTH is used. Other dynamic tests include the insulin tolerance test and the CRH stimulation test, which can help localize the defect to the pituitary versus the hypothalamus. Imaging with MRI of the pituitary gland and sella turcica is crucial to identify structural causes like a pituitary adenoma.

Treatment

The cornerstone of treatment is physiological glucocorticoid replacement therapy. Hydrocortisone is the preferred agent due to its short half-life, typically administered in two or three divided doses daily to mimic the normal circadian rhythm of cortisol secretion. Alternative steroids include prednisone or dexamethasone. Dosing must be individualized, with the lowest effective dose used to avoid side effects of iatrogenic Cushing's syndrome. During periods of physiological stress, such as febrile illness, trauma, or surgery, the dose must be increased significantly (stress-dose steroids) to prevent an adrenal crisis. Patient education on sick day rules and carrying a steroid emergency card is paramount. Any identified underlying cause, such as a pituitary adenoma, may require specific treatment by an endocrinologist or neurosurgeon.

Prognosis and complications

With appropriate diagnosis and lifelong glucocorticoid replacement, the prognosis for patients is generally excellent, allowing for a normal life expectancy and quality of life. The most serious acute complication is an adrenal crisis, which is a medical emergency requiring immediate parenteral hydrocortisone and fluid resuscitation. Long-term complications can arise from chronic over-replacement, leading to osteoporosis, hypertension, impaired glucose tolerance, and weight gain. Under-replacement results in persistent symptoms of fatigue and increased risk of crisis. Management requires regular follow-up with an endocrinologist to adjust doses and monitor for development of other pituitary hormone deficiencies, which are common in conditions like pituitary adenomas.

Category:Endocrine diseases Category:Adrenal gland disorders