Rare neuroendocrine tumours may be misdiagnosed as Cushing’s disease

By Eleanor McDermid, Senior medwireNews Reporter

Ectopic tumours secreting corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) are very rare in children and can result in a misdiagnosis of Cushing’s disease (CD), say researchers.

Three of the patients in the reported case series had pituitary hyperplasia and underwent transsphenoidal surgery for apparent CD before the tumour that was actually causing their symptoms was located. The hyperplasia was probably caused by release of CRH from the ectopic tumour, which stimulated the pituitary gland, giving the impression of an ACTH-secreting pituitary adenoma, explain Maya Lodish (National Institutes of Health, Bethesda, Maryland, USA) and study co-authors.

These three patients were part of a series of seven, which Lodish et al describe as “a relatively large number of patients, considering the infrequency of this disease.”

The patients were aged between 1.8 and 21.3 years. Three had neuroendocrine tumours located in the pancreas ranging in size from 1.4 to 7.0 cm, two had thymic carcinoids ranging from 6.0 mm to 11.5 cm, one patient had a 12.0 cm tumour in the liver and one had a 1.3 cm bronchogenic carcinoid tumour of the right pulmonary lobe.

Four of the patients had metastatic disease and, during up to 57 months of follow-up, three died of metastatic disease or associated complications and two patients had recurrent disease.

“Our series demonstrates that these are aggressive tumors with a high mortality rate,” write the researchers in the Journal of Clinical Endocrinology & Metabolism. “It is important to follow the appropriate work up, regarding both biochemical and imaging tests, which can lead to the correct diagnosis and to the most beneficial therapeutic approach.”

With regard to biochemical findings, they stress that “there is not always a specific pattern that can help us detect an ectopic ACTH/CRH-producing tumor, since the findings apparently depend strongly on the ratio of ACTH to CRH secretion.”

The team found the CRH stimulation test to be helpful, noting, for example, that none of the patients had a rise in cortisol that was consistent with CD, with all patients showing smaller responses ranging from 2% to 15%. Likewise, just one patient had an ACTH rise higher than 35% on CRH administration, and four patients had a “flat” response, which has previously been associated with ectopic neuroendocrine tumours.

Of note, six patients had normal or high plasma CRH levels, despite all having high cortisol levels, which would be expected to result in undetectable plasma CRH due to negative feedback, implying another source of CRH production. Five patients had blunted diurnal variation of both cortisol and ACTH levels consistent with Cushing’s syndrome.

The patients also underwent a variety of imaging procedures to identify the source of ACTH/CRH production, some of which, such as octreotide scans, are specialist and not available in most hospitals, the researchers note, potentially contributing to inappropriate diagnosis and management.

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