391- What are the causes of nodular goiter with cervical adenopathy?
The differential diagnosis for a nodular goiter with cervical adenopathy includes
papillary, medullary and anaplastic thyroid carcinoma, thyroid lymphoma, and
tuberculosis of the thyroid gland. Sometimes, subacute thyroiditis and pyo-
genic thyroid abscess can also lead to thyromegaly with cervical adenopathy.- What are the causes of high serum calcitonin other than MTC?
The disorders associated with high serum calcitonin levels other than MTC
include chronic renal failure, Hashimoto’s thyroiditis, PHPT, prostate and lung
cancer, mastocytosis, and neuroendocrine tumors. However, lack of rise in
serum calcitonin levels in response to calcium and pentagastrin differentiates
these disorders from MTC. Further, the use of DPP4 inhibitors, GLP1 agonists,
and proton pump inhibitors is associated with increased serum calcitonin levels.
Ingestion of food also results in raised serum calcitonin levels (entero- calcitonin
axis). The presence of heterophile antibodies interfere with the assay, thereby
may result in falsely elevated serum calcitonin. Therefore, serum calcitonin
level should be measured in the fasting state, and detailed drug history should
be elicited before interpreting high serum calcitonin levels.- What are the causes of low serum calcitonin in patients with MTC?
Low serum calcitonin levels in patients with MTC may occur as a result of “hook
effect” (prozone phenomenon) or poorly differentiated tumor. “Hook effect” can
be obviated by measuring the blood sample after dilution. Differentiated parafol-
licular C-cells produce high levels of serum calcitonin, whereas poorly differenti-
ated cells produce very low quantity of serum calcitonin and high levels of
carcinoembryonic antigen (CEA). Therefore, CEA levels may be helpful in mon-
itoring the progression of disease in patients with poorly differentiated
MTC. Further in a patient with neck mass and a FNAC proven MTC, the presence
of low serum calcitonin should raise a suspicion of other neuroendocrine tumor
(e.g., paraganglioma) after careful exclusion of “hook effect.”- What is C-cell hyperplasia?
C-cell hyperplasia (CCH) represents multicentric, clonal proliferation of para-
follicular C-cells and precedes the development of MTC. The diagnosis of
C-cell hyperplasia requires the presence of seven C-cells per cluster surrounded
by a normal follicle and extension of C-cells beyond the junction of the upper
third and lower two-thirds of the lateral lobes of the thyroid gland. Patients with
CCH should be evaluated for MEN2 syndrome after exclusion of secondary
causes of CCH, which include PHPT, renal failure, and Hashimoto’s
thyroiditis.11 Multiple Endocrine Neoplasia