A CASE OF MEDULLARY THYROID CARCINOMA WITH A TWIST !

Original case by I Huguet et al 

A 63-year-old woman was referred to our clinic following the incidental finding of a 1 cm thyroid nodule.

Q  What tests would you order on finding the thyroid nodule ?

  1. Review the ultrasound and physical examination findings
  2. A thyroid function test
  3. FNAC of the thyroid nodule if indicated

Q  What is the indication for FNAC according to new ATA 2015 guidelines ?

 

  1. High suspicion and intermediate suspicion- FNAC if nodule > 1 cm in size
  2. Low suspicion – FNAC if nodule > 1.5 cm in size
  3. Very low suspicion- FNAC if nodule > 2 cm in size
  4. Benign – avoid FNAC

 

Q  What are the high and intermediate risk features on ultrasound for which FNAC would be indicated in this case ?

Intermediate suspicion

  1. Hypoechoic with regular margins

High suspicion

  1. Hypoechoic + one of the following:
    1. Microcalcification
    2. Irregular margins
    3. Taller than wider
    4. Extrathyroidal extension
    5. Suspicious lymph nodes
    6. Interrupted calcification

Fine-needle aspiration cytology revealed a MTC.

Q  What are typical findings of MTC on FNAC ?

 

  1. Spindle shaped cells
  2. Cells have eccentric nuclei
  3. Amyloid like material in background

Q  How will you enhance the specificity of FNAC finding ?

Use of calcitonin staining in the FNAC smear- which will confirm the diagnosis of MTC.

Subsequently, plasma calcitonin levels were found to be elevated at 84 pg/ml (normal <11.5 pg/ml).

Q  What is the cutoff used for calcitonin in patients with Thyroid nodules for diagnosis of MTC ?

 

Basal calcitonin >20 pg/ml is suggestive of MTC and Pentagastrin stimulated Calcitonin >100 pg/ml confirms the diagnosis.

There were no other abnormal findings.

Q  What other tests would you perform ?

Since this patient has MTC, there is a high possibility of patient having MEN2. I would rule out pheochromocytoma and Hyperparathyroidism. I would clinically look for mucosal neuromas and marfanoid habitus.  (though MEN2B is less likely in this case considering the age of the patient).

The presence of a co-existing phaeochromocytoma was biochemically excluded (normal urinary catecholamine and metanephrine levels). Q  What is the ideal  surgery for this patient ?

Since the patient does not have lymph nodes involvement or metastasis and Calcitonin is between 20-200 pg/ml, the guidelines suggest total thyroidectomy with prophylactic central node dissection.

The patient was subjected to total thyroidectomy with clearance of central and lateral lymph node compartments.

The pathology demonstrated a calcified 1 cm nodule consisting of polygonal cells showing positive immunostaining for chromogranin, calcitonin, S-100 and carcinoembryonic antigen (CEA; Fig. 1). The lymph nodes were clear of disease.

Q  What is the next step for the disease ?

Genetic analysis is important to ascertain family risk and person risk of MEN2.

Genetic analysis of peripheral lymphocytes of the RET oncogene (automated sequencing of the flanking exons 10, 11, 13, 14, 15 and 16) did not reveal any germline mutation.

 

Q  How will you follow up this patient ?

I would repeat the Calcitonin and CEA after 3 months.

 

The patient recovered well from the operation, but exhibited persistently elevated plasma calcitonin levels, although she remained asymptomatic. Over the following 3 years, her plasma calcitonin levels were persistently elevated, although with no clear signs of progression (106, 116, 83, 173, 212, 279 and 114 pg/ml).

Q  What is done if calcitonin is persistently high after surgery ?

  1. If it is >150 pg/ml- then imaging is done
    1. USG/CT of neck
    2. CT thorax and abdomen
    3. Bone san
  2. If <150 pg/ml- follow-up.

Since this patient has calcitonin above 150 pg/ml on several occasions, an imaging is indicated.

Her circulating CEA levels remained normal. We suspected persisting or metastatic disease, but further repeated and detailed imaging including computed tomography (CT) and magnetic resonance (MR) scanning of the neck, chest and abdomen failed to reveal any evidence of tumour. Functional imaging with radiolabelled octreotide (Octreoscan) and fluorodeoxyglucose (FDG)-positron emission tomography (PET) scanning demonstrated mild uptake of both tracers in the midline, adjacent to L2, and further CT scanning was undertaken concentrating on this area. No clear abnormality was observed, and it was concluded at this stage that the apparent uptake was due to duodenal ‘physiological tracer elimination’.

However, after 3 years, the patient was found to have developed an iron-deficiency anaemia associated with positive faecal occult blood testing. Endoscopy was undertaken, and it showed chronic atrophic gastritis with intestinal metaplasia, but in addition a large (3 cm) polyp was found in the second part of the duodenum, which was biopsied.

The duodenal biopsy showed a NET, and the patient was subsequently re-explored surgically and partial duodenectomy was performed. Pathological examination confirmed a 2.8 cm well-differentiated NET with positive immunohistochemistry for CAM5.2, ac1-AE3, enolase, chromogranin, synaptophysin and serotonin; the Ki-67 index was <2% .

Q  What does a Ki-67 of <2% suggest ?

That it is a well differentiated neuroendocrine tumor.

Q  What is done for non-metastatic well differentiated carcinoid ?

Surgery and follow up.

Surprisingly, after resection of the duodenal tumour, circulating calcitonin levels remained repeatedly undetectable, and thus the tissue was immunostained for calcitonin; this was strongly positive.

Currently, the patient remains asymptomatic with persistently undetectable serum calcitonin levels and no further anaemia. She remains with mildly elevated serum chromogranin A and gastrin levels (last determination of serum gastrin levels: 591 pg/ml, normal <40; Fig. 3), which we attribute to her chronic atrophic gastritis.

Q  Can calcitonin be produced by other NET ?

Yes. It has been reported to be produced by other neuroendocrine tumors also.  In this case the association between the two seems coincidental.

 

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