Vol 75, No 1 (2024)
Clinical vignette
Published online: 2024-02-15

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A challenging case of ectopic ACTH-dependent Cushing’s syndrome due to medullary thyroid carcinoma

Maria Komisarz-Calik1, Paulina Sarba1, Małgorzata Trofimiuk-Müldner2, Grzegorz Sokołowski2, Joanna Szpor3, Alicja Hubalewska-Dydejczyk2
Pubmed: 38497400
Endokrynol Pol 2024;75(1):115-116.


Not required for Clinical Vignette.

Clinical vignette

Endokrynologia Polska

DOI: 10.5603/ep.96863

ISSN 0423–104X, e-ISSN 2299–8306

Volume/Tom 75; Number/Numer 1/2024

Submitted: 07.08.2023

Accepted: 25.10.2023

Early publication date: 15.02.2024

A challenging case of ectopic ACTH-dependent Cushing’s syndrome due to medullary thyroid carcinoma

Maria Komisarz-Calik1Paulina Sarba1Małgorzata Trofimiuk-Müldner2Grzegorz Sokołowski2Joanna Szpor3Alicja Hubalewska-Dydejczyk2
1Students’ Scientific Group of Endocrinology, Jagiellonian University Medical College, Cracow, Poland
2Department of Endocrinology, Jagiellonian University Medical College, Cracow, Poland
3Department of Pathomorphology, Jagiellonian University Medical College, Cracow, Poland

Malgorzata Trofimiuk-Müldner, MD PhD, Department of Endocrinology Jagiellonian University Medical College, ul. Jakubowskiego 2, 30–688 Kraków Poland, tel: +48 12 400 2332, fax: +48 12 424 73 99; e-mail: malgorzata.trofimiuk@uj.edu.pl, mtrofimiuk@gmail.com

This article is available in open access under Creative Common Attribution-Non-Commercial-No Derivatives 4.0 International (CC BY-NC-ND 4.0) license, allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially

Key words: medullary thyroid carcinoma; Cushing’s syndrome; ACTH-dependent Cushing’s syndrome; ectopic ACTH secretion

Medullary thyroid carcinoma (MTC) is an infrequent neoplasm originating from thyroid parafollicular cells. Calcitonin production is its distinguishing feature [1]. Due to its neuroendocrine provenience, MTC can release different active agents. Uncommonly, it can be a source of adrenocorticotropic hormone (ACTH), accounting for about 2% of ectopic Cushing’s syndrome (CS) [1].

We present a case of a 45-year-old male with an ectopic ACTH-dependent CS induced by MTC. The patient, with a history of recent diabetes and hypertension, was referred to the Endocrinology Department for suspicion of CS. He complained of increasing weakness, aggravating facial plethora, and weight gain. A 4-mm pituitary microadenoma was confirmed by magnetic resonance imaging 2 years prior to admission.

A loss of cortisol circadian rhythm, abnormal results of 1-mg (serum cortisol 23.6 µg/dL) and 8-mg dexamethasone suppression test (cortisol 25.6 µg/dL), as well as moderately increased concentration of ACTH (103.0–122.0 pg/mL), were revealed. In the corticotropin-releasing hormone (CRH) stimulation test the ACTH concentration increased by more than 35%. Other laboratory tests results are presented in Table 1. The diagnosis of ACTH-dependent CS was confirmed, and metyrapone was implemented.

Table 1. Other laboratory tests results



Reference range

Glucose (mmol/L)



FSH (mlU/mL)



LH (mlU/mL)


1.70– 8.60

TSH (μIU/mL)



FT4 (pmol/L)



IGF-1 (ng/mL)



Testosterone (nmol/L)












While searching for the source of ACTH secretion, positron emission tomography (PET/CT) with Gallium 68-tetraazacyclododecane-tetraacetic acid-octreotate ([68Ga]Ga-DOTA-TATE) was performed, showing heterogeneous expression of somatostatin receptors in enlarged thyroid (Fig. 1). On neck ultrasound, a 20-mm hypoechogenic thyroid nodule with irregular margins and sparse central vascularization was noted. Due to the presence of pituitary microadenoma and the CRH stimulation test results, the patient was scheduled for bilateral inferior petrosal sinus sampling (BIPSS), during which no significant ACTH surge or lateralization was observed. Therefore, planned transsphenoidal surgery was cancelled. Shortly after, the patient was readmitted due to aggravation of CS. Markedly increased calcitonin (> 1000.0 pg/mL) and procalcitonin (23.70 ng/mL) concentrations were noted. Thyroid cytology was classified as Bethesda VI. After stabilization of his general condition, the patient underwent a total thyroidectomy. Histopathological examination confirmed MTC, and immunohistochemical staining for ACTH was positive in approximately 10% of cells (Fig. 2). Genetic screening for germline pathogenic variants of RET protooncogene was inconclusive. After thyroidectomy, hypercortisolaemia symptoms markedly subsided, and the patient developed transient secondary adrenal insufficiency. Mildly elevated calcitonin concentrations showed a downward trend. Post-operative whole-body CT scan was negative for local and distant metastases.

Figure 1. [68Ga]Ga-DOTA-TATEPET/CT showing heterogeneous expression of somatostatin receptors in the enlarged thyroid gland (arrow)
Figure 2. Immunohistochemical staging of the medullary thyroid carcinoma (MTC). Tumour cells show positivity for calcitonin (A) (original magnification ×10) and adrenocorticotropic hormone (ACTH) (B) (original magnification ×40). Staining with haematoxylin and eosin (C) (original magnification ×10), and staining with Congo red (D) (original magnification ×20)

One and a half years after the surgery, Cushingoid features reappeared, and calcitonin, cortisol and ACTH concentrations markedly increased. Due to inoperative MTC local recurrence, vandetanib therapy has recently been initiated.

As the case illustrates, the first manifestation of MTC may be ectopic hypercortisolaemia. In the literature review by Barbosa et al., MTC-related CS accounted for 0.6% of all MTC patients [2].

Due to its rarity, diagnosing MTC-related CS can be difficult. Overlapping test results are the most common cause of Cushing’s disease (CD) and ectopic ACTH-dependent CS (EAS) misdiagnosis, and unnecessary therapeutic procedures. ACTH-dependent CS prompts pituitary imaging. If a pituitary adenoma of < 6–9 mm is present, further diagnostic work-up is warranted. Tests that may distinguish between CD and EAS include the high-dose dexamethasone suppression test (HDDST) and CRH stimulation test. An overnight HDDST has a specificity of 100% to exclude EAS [3]. However, some patients with EAS achieve suppression in HDDST [4]. CRH stimulation test has a lower rate of misdiagnosis than overnight HDDST among patients with EAS (30% vs. 50%), but HDDST combined with CRH stimulation does not improve the diagnostic accuracy [4]. Increased plasma ACTH and cortisol concentrations after CRH stimulation usually indicate CD [4]. In cases with discordant results of pituitary imaging and CRH test, BIPSS is considered the gold diagnostic standard for distinguishing EAS from CD [4]. Another significant EAS imaging tool is PET/CT scan with [68Ga]Ga-DOTATATE, which detects up to 65% of these tumours [5].

The reported case highlights the fact that despite the various diagnostic tools distinguishing between EAS and CS, it still poses a challenge. One should be aware of the inconsistent performance of diagnostic tests due to the variable biology of both ectopic ACTH-secreting tumours and pituitary adenomas. Cautious interpretation of laboratory tests and imaging results diminishes the likelihood of misdiagnosis. Furthermore, MTC should be considered as a potential cause of EAS, especially in patients with nodular goitre.

Author contributions

The authors’ contributions to the work were as follows. Conception of the article M.T-M., G.S.; design of the article, analysis of the data, writing of the manuscript M.K.-C., P.S.; acquisition of data, analysis and interpretation of data J.S., drafting the article or revising it critically for important intellectual content M.T.-M., final approval of the version to be published A.H.-D.


Not applicable.

Conflict of interest

None declared.


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