Malabsorption/carcinoid tumor Flashcards
Malaborption
general
Intestinal absorption refers to the assimilation of dietary fats, carbohydrates, proteins, vitamins, minerals, and trace elements into the systemic circulation.
Malabsorption refers to impaired transport of nutrients into the small intestines.
Fats
general
Ingested fats need to be in soluble form to digested (emulsified)
Mastication
Coated by gastric fluid
Emulsified fats are then move to the stomach where it is exposed to gastric lipase and in the duodenum to pancreatic lipase. Triglycerides are broken down into 2 monoglyceride and 2 fatty acids
The resulting mixture is a complex soup of lipolytic products. These products are mixed with bile salts to form micelles and are taken into enterocytes. Ideally in a pH of 6.5
Once taken up by peripheral tissues, can be used by muscles for energy or be stored in adipose tissue
Causes of Fat malabsorption
Decreased optimal duodenal pH < 6.5
Zollinger Ellison syndrome
Decreased intestinal surface area
Crohn disease
Celiac
Ulcerative colitis
Small bowel resection
Impaired lipid processing by bile acids
Liver disease
Cholestasis
Small intestinal bacterial overgrowth
Deconjugate bile acids, bile acids cannot absorb fats
Pancreatic insufficiency/cancer
Lymphatic system disorders
Intestinal lymphangiectasia
Whipple disease
Crohn’s Disease
general
Form of an inflammatory bowel disease
CD is characterized by transmural inflammation and may involve any portion of luminal gastrointestinal tract, from the oral cavity to the perianal area.
The pathophysiology is multifactorial
Relating to fat malabsorption
Bile acids form mixed micelles together with fatty acids, which function as a transport vehicle to deliver fatty acids to the apical membrane of enterocytes for absorption. Therefore, if the terminal ileum is impaired, bile acid malabsorption may occur, which may cause congenital diarrhoea in Crohn’s disease.
Fat malabsorption symptoms
Steatorrhea
Large pale stools/ “heavy stool”
In Average,200 grams for female adults and 220 grams for males. Patients with steatorrhea almost always have stool weights in excess of these values
Diarrhea without flatulence
Carbohydrates
general
Complex carbohydrates such as sucrose, starch, lactose are broken down into their monosaccharides prior to absorption
Salivary and pancreatic amylase aid in breakdown of complex carbohydrates
Carbohydrates that are not broken down in the SI and absorbed undergoes bacterial degradation in the colon.
Hydrogen and methane produced from fermentation of unabsorbed carbohydrates
This is excreted by the lungs. Non-invasive breath tests can be used to detect carbohydrate malabsorption.
Symptoms of carbohydrate malabsorption
Acidic stools
Abdominal distension
flatulence
Diarrhea
Causes of carbohydrate malabsorption
Deficiency in pancreatic amylase
Reduced disaccharidase activity in the small intestinal epithelium
Can co-exist in conditions such as IBD, colitis
Decreased absorptive intestinal surface area
eg, celiac disease
Unabsorbable carbohydrates
Low-digestible carbohydrates are carbohydrates that are incompletely or not absorbed in the small intestine but are at least partly fermented by bacteria in the large intestine. Fiber, resistant starch, and sugar alcohols are types of low-digestible carbohydrates.
Celiac disease
general
Immune disorder triggered by gluten in genetically predisposed individuals
Gliadin fractions (component of gluten) promote an inflammatory reaction causing chronic inflammatory cells and villous atrophy in SI.
Proteins
general
Starts in the stomach with gastric pepsin which releases amino acids
amino acids released from gastric digestion play a role in releasing cholecystokinin (CCK)
CCK is critical for stimulating the release of pancreatic enzymes responsible for the digestion of all three macronutrients.
In the duodenum, several proteases act together to digest proteins into amino acids, or dipeptides and tripeptides.
After breakdown into amino acids, dipeptides, and tripeptides, these are absorbed at the brush border membrane by secondary active transport
Causes of protein malabsorption
Pancreatic bicarbonate and protease secretion and/or activity is impaired
Chronic pancreatitis
Cystic Fibrosis
Diseases associated with a generalized reduction of the intestinal absorptive surface
Bowel resection
Crohn’s disease
Cystic fibrosis
general
Multisystem disorder caused by gene mutations resulting in abnormal transport of chloride and sodium across secretory epithelia. This causes thickened, viscous secretions in the bronchi, biliary tract, pancreas, intestines, and reproductive system
Protein malabsorption symptoms
Edema, hypoalbuminemia
Muscle atrophy
Amenorrhea
Chronic systemic illness such as IBD & celiac can cause inhibition of hypothalamic secretion and leads to amenorrhea.
Severe states
Pleural effusions
Ascites
Workup of malabsorption
If there is suspicion for malabsorption syndromes based on history and physical can approach the patient first with general testing.
Symptoms can be vague such as unintentional weight loss ongoing diarrhea, chronic abdominal pain
malaborption workup
Malabsorption Management
Treatment targets correcting deficiencies, treating the underlying cause, avoiding triggers (typically dietary), and treating symptoms (e,g often diarrhea).
Celiac disease: avoid gluten
Zollinger Ellison: PPI to reduce acidity to improve fat absorption
Pancreatic insufficiency: pancreatic enzyme replacement
SIBO: antibiotics
Diarrhea
Loperamide or diphenoxylate with atropine if severe
Oral Rehydration
Carcinoid Tumors & Carcinoid Syndrome
general
Small, well-differentiated, slow-growing neuroendocrine tumors (NET)
Develop from neuroendocrine cells for reasons unknown
Gastrointestinal tract (90%)
Pulmonary bronchi
Pancreas
Genitourinary tract (rare)
Benign, locally invasive, or malignant
Incidence:
Rare, but ↑ incidence due to improved detection
More prevalent in patients 50-70 years
Blacks > Whites – GI carcinoid tumors
Whites > Blacks – pulmonary carcinoid tumors
Carcinoid Syndrome
general
Describes the signs and symptoms associated with unregulated vasoactive hormone production by neuroendocrine tumors upon metastasis to the liver
Develops in ~5% of carcinoid tumors
Carcinoid Syndrome
Secreted substances
Stomach carcinoids:
Histamine
Lung/bronchial carcinoids:
Histamine
Serotonin
Gastrin
Adrenocorticotropic hormone (ACTH)
Carcinoid Syndrome
Clinical Presentation
Episodic cutaneous flushing- most commonand often earliest sign
Dependent on the anatomical location of the tumor
Lasts minutes to hours
Precipitated by emotional stress or the ingestion of food, hot beverages, or alcohol
Abdominal cramping
Recurrent diarrhea
↑ bowel motility
Bronchospasm → shortness of breath
Hepatomegaly
Cardiac valvular lesions
Muscle wasting
carcinoid tumor
labs for Dx
Labs
24-hour urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA)
Preferred initial test
Measurement of the end-product of serotonin metabolism
≥ 25 mg/dayis diagnostic
Direct measurement of blood serotonin levels is not recommended – false positives
carcinoid tumor
imaging
Imaging
CT scan or MRI
Localize the primary tumor
Assess extent of tumor spread and metastases
Liver- Most common distant metastatic site
Liver metastases is best assessed with MRI
Endoscopy with biopsy
Upper and lower endoscopy should be performed for metastases with an unknown primary tumor
carcinoid tumor
Primary tumor management
Surgical resection - first-line treatment
Reduces tumor mass
Often curative for primary gastrointestinal and lung carcinoids
carcinoid tumor
Carcinoid syndrome and metastatic disease
Tx and meds
Somatostatin analogs to inhibit serotonin secretion
Octreotide
Bind to somatostatin receptors and inhibit serotonin release
Provide symptomatic relief (50–70% of patients)
Inhibit proliferation of tumor cells
Hepatic resection:
Can be curative for resectable liver lesions
Can serve as palliation for carcinoid syndrome
Performed if > 90% of tumor can be resected/ablated
