Cushing's Disease
Definition and Presentation
A disease caused by overproduction of cortisone. The
overproduction is stimulated by an excess of the pituitary hormone
ACTH that regulates adrenal gland production of cortisone. In
Cushing's disease the ACTH overproduction usually comes from a
benign tumour in, or very close to the pituitary gland. In
Cushing's syndrome the clinical features are the same as in
Cushing's disease but the ACTH regulatory hormone emanates from a
tumour in another location or by a condition in the adrenal gland
itself. A Cushing syndrome can also be produced by medication with
cortisone or cortisone derivatives.
A patient with pronounced Cushing's
disease may present with the classic features of moon-face,
redistribution of fat to abdomen and upper back, thin skin with
bruising and hypertension. There may also be emotional disorders,
back pain from decalcification from the skeleton and generalised
muscular weakness. In more than 50% of the patients only a milder
form of the characteristic symptoms are found. Due to hypertension,
hypercholesterolemia and impaired immune function, patients with an
active untreated disease run a risk of death from cardiovascular
and infectious complications.
Diagnosis
The ultimate diagnosis rests on
an assessment of cortisol and ACTH hormone levels in the blood.
Only 60% of ACTH producing pituitary tumours can be visualised by
MRI. Cushing's disease is established when it can be shown that the
increased level of cortisol in the blood is caused by an excessive
ACTH production from the pituitary gland. Sometimes blood sampling
from veins draining the pituitary area as well as from peripheral
blood is required.
Treatment
Many pituitary tumours producing excessive ACTH (or so-called
microadenomas) are less than 5mm in diameter and some are not
visible on MRI scans. However, most of them can be identified
during transphenoidal surgery. This is therefore the treatment of
choice when diagnosis has been established. The success rate is
65-85%. The risk of recurring disease is 10-20%. It has been shown
that Gamma Knife surgery up-front can be equally effective but due
to the frequent problems of visualisation of the small tumour it is
still not considered the primary choice. This may change with
improving imaging techniques. Cortisol production and the
manifestations of the disease can also be suppressed by certain
drugs (e.g. ketoconazole). Drug treatment is currently recommended
only as a temporary solution when the patient is awaiting
definitive treatment.