Pancreatic carcinoid - Diagnosis

Pancreatic carcinoid in the absence or incomplete carcinoid syndrome (about 80% of cases) remains unrecognized or is diagnosed incidentally. In the presence of a severe carcinoid syndrome, the diagnosis is confirmed (in the presence of a pancreatic tumor) by determining the elevated blood serotonin content and increased urinary excretion of its metabolite 5-HIAA. Before the study, all medications (primarily phenothiazines, reserpine-containing drugs, laxatives, diuretics) should be discontinued for 3-4 days. Serotonin- and tryptophan-containing foods (bananas, walnuts, pineapples, avocados, plums, currants, tomatoes, eggplants, cheddar cheese) should be excluded from the diet. The upper limit of normal daily excretion of 5-HIAA is 10 mg. Excretion of 10-25 mg 5-HIAA per day is suspicious for the presence of carcinoid. Values above 25 mg/day are pathognomonic for this pathology. In doubtful cases, a provocative test is performed with reserpine, which releases serotonin from both brain cells and peripheral depots and prevents its binding in tissues and thrombocytes. In healthy individuals, daily excretion of 5-HIAA with urine after taking reserpine increases only in the first hours, then normalizes.

In carcinoid tumors, a sharply increased release of 5-HIAA is observed for many hours.

In addition to carcinoid, increased excretion of 5-HIAA may be observed in a number of diseases that should be taken into account in differential diagnostics - sprue, Whipple's disease, intestinal obstruction, malabsorption. In all of the above cases, if an increase in the daily excretion of 5-HIAA is determined, it is small, often transient, and is not accompanied by other symptoms of carcinoid or an increase in the concentration of serotonin in the blood.

Portal hypertension often leads to an increase in the blood serotonin content. However, such patients lack signs of the general endocrine action of the amine and have symptoms of liver pathology, in which serotonin metabolism is often disrupted.

At the onset of the disease, some similarity of the clinical picture with pheochromocytoma is possible, due to the similarity of the chemical structure of the humoral substances produced by both tumors. In addition, with pheochromocytoma, the excretion of 5-HIAA may be increased due to the displacement of serotonin from the depot by an excess amount of catecholamines. On the contrary, excess serotonin in carcinoid can displace catecholamines from the depot and cause adrenergic effects. This explains the similarity of a number of symptoms in the two tumors under consideration. However, with carcinoid, there are no metabolic disorders characteristic of pheochromocytoma - carbohydrate metabolism disorders, increased basal metabolism. If arterial hypertension is observed in patients with a carcinoid tumor, it is short-term, occurring during a hot flash with a subsequent drop in arterial pressure. In pheochromocytoma, the increase in arterial pressure can be both paroxysmal and persistent, accompanied by changes in the left ventricle of the heart, and not its right sections. Of decisive importance in differential diagnostics is the determination of humoral substances produced by these tumors and their metabolites in the blood and urine.

A carcinoid tumor may be similar in clinical presentation to a mastocytoma, whose cells produce histamine and heparin. Measuring their concentration in the blood helps to avoid diagnostic errors.

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