Adrenal insufficiency
·
1o adrenal failure: results in both reduced
glucocorticoid (cortisol) and mineralocorticoid
(aldosterone) production. Adrenocorticotrophin (ACTH) levels are elevated due
to reduced cortisol negative feedback drive.
·
2o adrenal failure: is due to either reduced
corticotrophin-releasing factor
(CoRF) or reduced ACTH production (or both) and results in reduced cortisol
production only. Mineralocorticoid activity remains normal as this is mainly
regulated by the angiotensin–renin system.
· Autoimmune adrenalitis (Addison’s
disease).
· Adrenal infection, e.g. tuberculosis.
· Adrenal haemorrhage/infarction.
· Latrogenic: adrenolectomy; drugs
(e.g. ketoconazole).
· Congenital adrenal hyperplasia.
· Congenital adrenal hypoplasia.
· Adrenoleucodystrophy.
· Familial glucocorticoid
deficiency.
· Defects of hypothalamus/pituitary
structures:
· congenital—pituitary hypoplasia;
· intracranial masses: tumours (e.g.
glioma, germinoma); craniopharyngioma;
· intracranial inflammation:
Langerhan’s histiocytosis;
· intracranial infections;
· cranial radiotherapy/irradiation;
· neurosurgery;
· traumatic brain injury.
· Suppression of
hypothalamic–pituitary–adrenal axis:
· glucocorticoid therapy;
Cushing’s disease (after pituitary
tumour removal).
The age of onset and
manifestations will depend on the underlying cause. Clinical features may be
subtle and a high index of suspicion is often re-quired. Typically, clinical
features are gradual in onset with partial insuf-ficiency leading to complete
adrenal insufficiency with impaired cortisol responses to stress and illness
(adrenal crises):
·anorexia and weight loss;
·fatigue and generalized weakness;
·dizziness (hypotension);
·salt craving (primary adrenal
insufficiency);
·hyperpigmentation (primary adrenal
insufficiency);
·reduced pubic/axillary hair
(primary adrenal insufficiency);
·hypoglycaemia (neonates/infants).
Note:
Random basal cortisol levels are
often within the normal range and cannot
be relied on. Inappropriately low basal cortisol during ‘stress’ sug-gests
adrenal insufficiency. A basal cortisol level of >550nmol/L usually excludes
this diagnosis. An elevated early morning (09.00 hours) ACTH level for the
level of cortisol is suggestive of primary adrenal insufficiency.
Usually required to establish a
diagnosis of adrenal insufficiency and are used to demonstrate inappropriately
low serum cortisol responses to physiological or pharmacological stimulation of
the adrenal glands.
·Insulin
tolerance test: considered
the gold standard test. Insulin-induced mild
hypoglycaemia is used to assess the integrity of the entire
hypothalamic–pituitary–adrenal axis. Serum cortisol response to hypoglycaemia
(>550nmol/L) is normal.
·ACTH
stimulation (synacthen) test: serum cortisol is measured at
baseline and at +30 and +60min after IV/IM of synthetic ACTH (short
synacthen test). Serum cortisol response >550nmol/L at 60min is considered
normal. Recent onset secondary adrenal insufficiency may produce a normal
response to a short synacthen test.
·Serum
electrolytes: serum
sodium (low); serum potassium (high).
·Adrenal antibody titres (Addison’s
disease).
·Adrenal
imaging: US; CT scan.
·Adrenal androgen profile:
serum/urine.
·Molecular genetic studies.
Pituitary
imaging: CT or MRI scan
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