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Cushing syndrome due to macronodular adrenal hyperplasia
ACTH-independent macronodular adrenal hyperplasia (AIMAH) is a rare cause of Cushing syndrome (CS; see this term) characterized by nodular enlargement of both adrenal glands (multiple nodules above 1 cm in diameter) that produce excess cortisol and features of adrenocorticotropic hormone (ACTH) independent CS (see this term).
Prevalence of endogenous CS is estimated at 1/26,000 and AIMAH represents less than 1% of the cases.
The disease presents a bimodal age distribution with a rare subset presenting in the first years of life, particularly associated to McCune-Albright syndrome (MAS; see this term). Most patients present in their 5th or 6th decade and the disease might be more prevalent in females. AIMAH most frequently presents as clinical or subclinical CS and signs usually become apparent only after several decades of life. However, in some patients the adrenal lesions are found incidentally, in the process of radiological investigation of another disease. The adrenal glands can be massively enlarged bilaterally with the presence of numerous macronodules; however diffuse adrenal enlargement without nodules has been described.
The exact etiology is unknown but the adrenal overgrowth seen in AIMAH may be due to the expression of aberrant membrane receptors found in the adrenal cortex that regulate cortisol secretion and which are stimulated by gastric inhibitory polypeptide (GIP), vasopressin, serotonin, catecholamines and luteinizing hormone (LH).
Diagnosis is based on the clinical picture of CS, the demonstration of ACTH-independent hypercortisolism (decreased levels of ACTH in plasma, non suppressible cortisol level after dexamethasone administration), and bilateral adrenal nodular enlargement on radiological imaging. Diagnosis is often difficult because hypercortisolism usually develops slowly over years, may be cyclical and is often associated with subtle CS. Radiological imaging is helpful, but occasionally nodularity is indistinguishable from that in normal elderly persons. Diagnosis can be confirmed by histological examination. Hormonal investigations can demonstrate aberrant receptor expression with abnormal stimulation of cortisol secretion by various hormones such as GIP in cases of food-dependent CS and gonadotropin-releasing hormone (GnRH) in cases of LH-dependent CS.
Differential diagnoses include other causes of ACTH-independent CS (adrenal adenoma and carcinoma), ACTH-dependent CS including pituitary (Cushing disease) or extra-pituitary tumors (ectopic ACTH secretion; see these terms), polycystic ovary syndrome and metabolic syndrome.
AIMAH is most often reported as sporadic but there are increasing reports of familial cases with autosomal dominant transmission. As the genetics of this disease are largely unknown genetic counseling is not yet possible.
Management and treatment
Treatment can be medical if aberrant adrenal receptors are identified and can be blocked (i.e. with propranolol, somatostatin or GnRH analogs). If the blockade is not possible, treatment will be chosen depending on the level of steroid excess. Unilateral adrenalectomy can be proposed for patients with a moderate increase in hormone production, while bilateral adrenalectomy is recommended for patients with significant overproduction. After bilateral adrenalectomy, glucocorticoid and mineralocorticoid replacement is required.
Prognosis after treatment is good but quality of life may be affected due to the long-term effects of hypercortisolemia. Without treatment the disease is life-threatening as in the case of manifest hypercortisolism. In cases of moderate hypercortisolism, long-term morbidity is due to the increased cardiovascular and metabolic risk factors associated with mild CS.
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