Carcinoid syndrome and multiple endocrine neoplasia – etiology, pathogenesis, and clinical manifestations.
Carcinoid Syndrome
Carcinoid syndrome is a set of systemic symptoms caused by hormone-secreting neuroendocrine tumors, mainly those that produce serotonin.
Etiology
- Usually due to metastatic neuroendocrine tumors (carcinoid tumors ) arising from:
- Gastrointestinal tract (most common: small intestine).
- Bronchial system (lungs).
- Liver metastases are important because liver normally metabolizes serotonin → when metastasized, excess hormones enter systemic circulation.
Pathogenesis
- Tumor cells produce serotonin (5-HT), histamine, kallikrein, and other vasoactive substances.
- These substances enter systemic circulation (especially if liver metastases bypass hepatic metabolism).
- Cause a variety of systemic effects, particularly on blood vessels and smooth muscles.
Clinical manifestations
- Flushing of face and upper chest (episodic, red-hot feeling).
- Diarrhea (due to increased gut motility).
- Bronchospasm (wheezing, asthma-like attacks).
- Right-sided heart valvular lesions (pulmonary stenosis, tricuspid regurgitation).
- Abdominal cramping.
- Niacin deficiency (pellagra-like symptoms: dermatitis, diarrhea, dementia) — because tryptophan is diverted to serotonin synthesis.
Multiple Endocrine Neoplasia (MEN)
Definition
MEN syndromes are inherited disorders characterized by tumors in multiple endocrine glands, often functional (hormone-secreting).
Etiology
- Genetic, autosomal dominant inheritance.
- Mutations:
- MEN1 gene (menin tumor suppressor protein) → MEN type 1.
- RET proto-oncogene mutations → MEN type 2A and 2B.
Classification and pathogenesis
MEN type 1 (Wermer syndrome)
- Mutation: MEN1 gene.
- Tumor types (3 Ps):
- Parathyroid hyperplasia/adenomas → hypercalcemia.
- Pancreatic neuroendocrine tumors → gastrinoma (Zollinger-Ellison syndrome), insulinoma.
- Pituitary adenomas → prolactinoma most common.
MEN type 2A (Sipple syndrome)
- Mutation: RET proto-oncogene.
- Tumor types:
- Medullary thyroid carcinoma (calcitonin-producing, aggressive).
- Pheochromocytoma (hypertension, catecholamine excess).
- Parathyroid hyperplasia → hypercalcemia.
MEN type 2B
- Mutation: RET proto-oncogene (different site).
- Tumor types:
- Medullary thyroid carcinoma (more aggressive).
- Pheochromocytoma.
- Mucosal and intestinal ganglioneuromas (lips, tongue, gut).
Clinical manifestations
MEN type 1
- Hypercalcemia symptoms: kidney stones, bone pain, abdominal pain.
- Peptic ulcers and diarrhea (gastrinoma ).
- Signs of prolactinoma: galactorrhea, amenorrhea in women; decreased libido in men.
MEN type 2A
- Neck mass or thyroid nodule (medullary carcinoma).
- Episodic hypertension, palpitations (pheochromocytoma).
- Hypercalcemia symptoms if parathyroid involved.
MEN type 2B
- Marfanoid habitus (tall, thin, long limbs).
- Mucosal neuromas: nodules on lips and tongue.
- Early aggressive thyroid cancer and pheochromocytoma.