Endocrine Abstracts

The diagnosis of Cushing’s syndrome firstly involves making or excluding the diagnosis. If the diagnosis is confirmed then an accurate diagnosis is needed as treatment modalities are in general specific to the aetiology. The diagnosis can be straightforward when symptoms and signs are classical and advanced. In these patients 24 h urinary free cortisol levels are markedly raised, late evening serum and salivary cortisol levels are raised and there is failure to suppress serum cortisol to control levels after low dose dexamethasone suppression. However because the clinical manifestations are often nonspecific the diagnosis can often be challenging. Difficulties also occur in cases with less marked or variable elevations in 24 h urinary cortisol and in those with concomitant conditions such as alcohol dependency, depression. In such cases it can be difficult to exclude or definitively diagnose the syndrome and in all a careful clinical judgment has to be made as to when to stop investigating. In some cases extended collections are required to establish cyclical or episodic unpredictable production and in others an extended time of observation confirms or refutes the diagnosis.

The differential diagnosis of adrenal adenoma and carcinoma is usually clear with suppressed ACTH level and unilateral adrenal mass on scanning. Investigations for other causes of ACTH-independent hypercortisolism must be considered when ACTH levels are suppressed and there is no unilateral abnormality. These include abnormal receptor regulation and function.

Perhaps the most difficult problem is in the differential diagnosis of ACTH-dependent cases. After a review of our Belfast experience looking at stringent responses to high dose dexamethasone testing and CRH testing, and bilateral inferior petrosal sinus sampling (IPSS) we concluded that the best evidence was from IPSS and that it is still required in a significant proportion of patients.

Illustrative cases will be presented and discussed.