Monday, June 20, 2011

Diarrhea Case 1

A 52-year-old woman consults a physician because she has been having increasingly frequent episodes of abdominal cramps and diarrhea.
These episodes are accompanied by an uncomfortable flushing of her skin. She thinks they are sometimes precipitated by eating, alcohoI, or emotional distress, but she has also recently been having episodes that had no obvious trigger.
Q 1
Her physician suspects that she may have a hormone-secreting tumor. Ectopic secretion of which of the following substances would be most
Iikely to cause diarrhea?
/ A. Gastrin
/ B. GIucagon
/ C. Histamine
/ D. Insulin
/ E. Serotonin
Which of the following laboratory tests would be most appropriate to test for excess secretion of the hormone causing the diarrhea?
/ A. Dexamethasone test
/ B. Hemoglobin A1C
/ C. Urinary 5-hydroxyindoleacetic acid
/ D. Urinary aminolevulinic acid
/ E. Urinary porphobilinogen
Q 3
CT scan demonstrates several probable metastatic tumors in the patient's liver. These are most likely which of the following histologic types?
/ A. Burkitt lymphoma
/ B. Carcinoid tumor
/ C. Hepatocellular carcinoma
/ D. Kaposi sarcoma
/ E. Squamous cell carcinoma
Q 4
The metastases most likely originated from which of the following?
/ A. Central nervous system
/ B. Gastrointestinal tract
/ C. Reproductive tract
/ D. Respiratory tract
Q 5
These tumors are thought to be derived from which of the following cell lines?
/ A. Endothelial cells
/ B. Enterochromaffin cells
/ C. Fibroblasts
/ D. Lymphocytes
/ E. Smooth muscle cells

Diarrhea Case 1 Answers
The correct answer is E. Excess serotonin can act on smooth muscle to produce diarrhea, colic, and malabsorption.
Excess gastrin secretion (choice A) can cause peptic ulceration secondary to stimulation of gastric glands.
Excess glucagon secretion (choice B) can cause rash and impaired glucose tolerance.
Excess histamine secretion (choice C), as well as excess bradykinin secretion, can coexist with excess serotonin secretion, and can contribute to the flushing seen in this patient.
Excess insulin secretion (choice D) can cause hypoglycemia.
The correct answer is C. 5-hydroxyindoleacetic acid is the major urinary metabolite of serotonin.
The dexamethasone test (choice A) is used to screen for Cushing syndrome.
Hemoglobin A1c (choice B) is a marker for long-term glycemic control.
Urinary porphobilinogen (choice E) and urinary aminolevulinic acid (choice D) are used in the diagnosis of the porphyrias.
The correct answer is B. The patient's clinical presentation is typical for carcinoid syndrome, which is a clinical manifestation of hormone-secreting carcinoid tumors. It is usually seen in the presence of metastatic disease involving the liver. None of the other tumors listed would be expected to secrete hormones.
The correct answer is B. Approximately 90% of carcinoid tumors occur in the gastrointestinal tract, with the most common site in the gastrointestinal tract being the small intestine (39%, data from web site). Involvement of the appendix (26%) and rectum (15%) is also fairly common. Other sites include colon (5-7%), stomach (2-4%), pancreas (2-3%), liver (less than 1%), bronchial system (10%, choice D), and rarely gonads (choice C), gallbladder and bile ducts, urinary bladder and kidneys (choice E), prostate, breast, and thymus. The central nervous system (choice A) does not appear to be a significant site of origin.
The correct answer is B. Carcinoid tumors are thought to be derived from the glandular endocrine hormone-producing cells, known as enterochromaffin cells, which are widely distributed through the body. They occupy a borderline category between benign and malignant, because only a fairly small percentage of them eventually metastasize, and pathologists are unable, histologically, to tell which ones will or will not. Most of the malignant ones are derived from the small intestine (1/5 metastasize and 1/3 of those cause carcinoid syndrome), and they tend to produce the clinical symptoms of carcinoid syndrome illustrated in the case history only when they have metastasized to the liver. The tumors probably secrete hormones prior to metastasis; the absence of carcinoid syndrome in these patients is attributed to the fact that the venous drainage of the gut passes through the liver via the portal system, clearing the blood of excess vasoactive substances. Also, some of the tumors do not secrete clinically significant amounts of hormones. Serotonin, histamine, and bradykinin are the most common hormones secreted that produce symptoms. Carcinoid tumors are found incidentally in approximately 0.5% of appendectomy specimens; appendiceal carcinoids only rarely metastasize. The tumors may also be a component of the multiple endocrine neoplasia (MEN) syndromes. Tumors that are identified incidentally before metastasis can be cured surgically. No effective chemotherapy or radiotherapy is available for metastatic disease, but the tumors grow so slowly that 10-15 year survival times are not unusual. The somatostatin analog octreotide can help control symptoms.
Endothelial cells (choice A) give rise to vascular tumors such as Kaposi sarcoma and angiosarcoma.
Fibroblasts (choice C) can give rise to a variety of fibromas and fibrosarcomas.
Lymphocytes (choice D) can give rise to leukemias and lymphomas.
Smooth muscle cells (choice E) can give rise to leiomyomas and leiomyosarcomas.

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