Differential diagnosis of Cushing’s syndrome

Factitious Cushing’s syndrome is extremely rare. The diagnosis is challenging as cross-reactivity of synthetic corticosteroids or their metabolites in immunoassay measurements of plasma or urinary cortisol can make distinguishing between true and factitious Cushing’s syndrome difficult. Thynne et al. report on a case of a 54-year old woman who presented with clinical and biochemical features of Cushing’s syndrome and an unsuppressed ACTH concentration.  They show that the key to the diagnosis of factitious Cushing’s syndrome in their patient was the recognition of the discordance between the normal plasma cortisol, mildly elevated salivary cortisol, and marked elevation of urine cortisol concentrations. This discrepancy was present during the initial investigations, but the significance was not fully appreciated until treatment with ketoconazole amplified the discordance. Factitious Cushing’s syndrome can mimic endogenous ACTH-dependent hypercortisolism during initial investigations and inferior petrosal sinus sampling (IPSS). This case highlights the importance of (i) recognizing the significance of discordant results; (ii) using an ACTH assay capable of reliably differentiating ACTH-dependent from ACTH-independent Cushing’s syndrome; and (iii) appreciating that IPSS is only useful to localize the source of ACTH in confirmed ACTH-dependent Cushing’s syndrome. In this case, measurement of co...
Source: Society for Endocrinology - Category: Endocrinology Source Type: news