A 61-year-old man presents with generalised weakness and skin hyperpigmentation. His only past medical history of note is a bilateral adrenalectomy for Cushing’s syndrome 18 years earlier. On examination of his visual fields you discover a bitemporal hemianopia.
1. What is the most likely diagnosis?
This patient has a diagnosis of Nelson’s syndrome.
Nelson’s syndrome is a rare condition that occurs many years after a bilateral adrenalectomy for Cushing’s syndrome. It is thought that it develops due to loss of the negative feedback control that usually suppresses high cortisol levels. This in turn results in the re-establishment of CRH production by the hypothalamus, which subsequently goes on to stimulate growth of an adrenocorticotrophic hormone (ACTH) producing pituitary adenoma.
2. Why is this condition only seen rarely?
It is now very rarely seen as the procedure is no longer commonly performed. Even in patients that have had a bilateral adrenalectomy for a pituitary adenoma, only between 20-40% would go on to develop Nelson’s syndrome.
The following risk factors can help to predict which patients are likely to develop it:
- High ACTH levels one-year post adrenalectomy
- A long duration of Cushing’s disease prior to adrenalectomy
- Adrenalectomy performed at a younger age (children much higher risk)
3. What other symptoms and signs might you expect to be present?
Symptoms and signs relate to the growth of the pituitary adenoma and subsequent increased production of ACTH and melanocyte stimulating hormone (MSH) from the adenoma:
- Visual field defects (up to 50%)
- Increased skin pigmentation (linea nigra also often present)
- Hypopituitarism can also occur
4. What investigations should be performed?
ACTH levels will be markedly elevated (usually > 500 ng/L). MRI or CT scanning is helpful to identify the presence of an expanding pituitary mass. Thyroxine, TSH, gonadotrophin and sex hormone levels may all be low. Prolactin levels may be high but not as high as with a prolactin-producing tumour.
5. How is this condition managed?
A transsphenoidal resection of the pituitary is the treatment of choice, particularly in cases such as this where there is compression of the optic chiasm. There is a higher success rate for smaller tumours. For invasive adenomas that show evidence of progression radiotherapy may be the preferred option.
Medical therapy with dopamine agonists, such as cabergoline and bromocriptine, can be used in certain cases, but are generally less effective than surgery.
Prognosis is good if the condition is detected early enough. The overall mortality rate is currently around 5%.
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