ACTH-independent macronodular adrenal hyperplasia
Other Names: AIMAH; Massive macronodular adrenocortical disease; MMAD; Adrenocorticotropic hormone-independent macronodular adrenal hyperplasia; Corticotropin-independent macronodular adrenal hyperplasia; ACTH-independent macronodular adrenocortical hyperplasia; Primary macronodular adrenal hyperplasia
A rare cause of Cushing syndrome (CS) 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.
Prevalence of endogenous CS is estimated at 1/26,000 and Cushing syndrome due to macronodular adrenal hyperplasia (CSMAH) represents less than 1% of the cases.
The exact etiology is unknown but the adrenal overgrowth seen in CSMAH 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).
Signs and symptoms
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. CSMAH 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.
For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms
- Failure to thrive(Faltering weight)
- Macronodular adrenal hyperplasia
- Round face(Circular face)
- Thin skin
- Truncal obesity
30%-79% of people have these symptoms
- Bruising susceptibility(Bruise easily)
- Diabetes mellitus
- Generalized hirsutism(Excessive hairiness over body)
- Muscle weakness(Muscular weakness)
- Nephrolithiasis(Kidney stones)
5%-29% of people have these symptoms
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 diagnosis 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.
CSMAH 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.
NIH genetic and rare disease info
ACTH-independent macronodular adrenal hyperplasia is a rare disease.