Diarrhea by Melanie Baskind and Dr. Bridget Hron.
Learning Objectives.
By the end of this video, the viewer
should be able to: review the basic pathophysiology
of diarrhea, describe the clinical presentation
of a pediatric patient with diarrhea,
develop a differential diagnosis for a pediatric patient
with diarrhea, and understand the management of a child who
presents with diarrhea.
Introduction.
Diarrhea, as defined by the World Health Organization,
is the passage of three or more loose or watery stools per day.
In practice, stool volume and consistency can vary greatly.
An infant may have eight loose stools
daily, which may be normal.
And a toddler may have three loose stools daily,
which may also be normal.
Therefore, trying to determine whether there
is a significant change in the frequency and consistency
of stool compared with baseline can be used
as a helpful gauge of diarrhea.
Worldwide, diarrhea is the second leading
cause of death in children under the age of five, and in the US,
accounts for more than 1.5 million outpatient visits
and 200,000 hospitalizations each year.
Diarrhea is one of the most common chief complaints
pediatricians confront, and there are many causes of it.
Most episodes are acute and can be managed in the outpatient
setting, but signs of dehydration
and specific history and physical exam findings
may warrant a more nuanced approach.
Pathophysiology.
Diarrhea occurs when excessive fluid
remains within the lumen of the intestine.
As such, diarrhea can be caused by fluid over secretion,
under absorption, or rapid transport that effectively
bypasses this process.
As water moves passively across the intestinal epithelium,
its relative volume in the lumen is determined
by osmotic gradients.
The transport of sodium and chloride
play the greatest role in this balance.
The villus epithelial cells of small intestine
cause a net absorption of sodium and the crypt epithelial cells
cause a net secretion of chloride.
Again, we're referring to net secretion and absorption.
Sodium absorption is not strictly compartmentalized
in the villus cells, and chloride secretion
is not strictly compartmentalized
in the crypt cells.
An increase in the secretion of fluid into the lumen referred
to as secretory, or electrolyte transport induced diarrhea,
is the result of an alteration in the ion transport
mechanism in epithelial cells.
A classic example of secretory diarrhea
is Cholera, where the produce toxin induces
excessive chloride transport, causing
large and life-threatening movement of chloride and water
into the lumen of the intestine.
Additional etiologies of secretary diarrheas
include other enterotoxigenic microbes,
congenital enteropathies, and diarrhea
mediated by gastrointestinal peptides,
such as VIP and gastrin.
Another kind of diarrhea, termed osmotic,
or diet induced diarrhea, occurs when
osmotically active substances remain in the lumen
and lead to water retention and loss of fluid absorption.
This may occur in the presence of a non-absorbable solute
such as polyethylene glycol, or be due to reduced nutrient
absorption.
Examples of reduced nutrient absorption
include enzyme deficiencies that prevent
the breakdown of certain sugars, such as lactase deficiency
or damage to the epithelial cells by infection,
inflammation, or an autoimmune process,
which reduces its absorptive capacity.
To determine whether the diarrhea is predominantly
osmotic or secretory, providers can test stool and calculate
a fecal osmotic gap in mOsm per kilogram,
which is equal to 290 minus 2 times the stool sodium
plus the stool potassium.
Osmotic diarrheas are defined as having
a gap greater than 75 mOsm per kilogram,
or 100 mOsm per kilogram, depending on the reference,
with higher values being more specific.
And secretory diarrhea is defined
as having a gap less than 50 mOsm per kilogram.
While it can be useful to think about the pathophysiology
of diarrhea as either secretory or osmotic,
in reality, many diarrheas are a mix
of the two processes, which is often related
to the nutrient intake at the time of stool testing.
Clinical Presentation.
Despite the World Health Organization definition,
any significant change in a child's normal stooling pattern
should prompt evaluation, with greater concern for children
who are ill appearing, show signs of dehydration,
have blood or mucus in their stool,
or have underlying medical conditions.
Because of the wide variety of etiologies of diarrhea,
a thorough history and physical exam
are critical to guide appropriate management.
All children presenting with diarrhea
must be evaluated for hydration status.
Providers should be attuned to acute weight changes
and ask about the child's oral intake and urine output
or number of wet diapers.
On physical exam, look for signs of dehydration
such as sunken eyes, sunken fontanel in infants,
tachycardia, dry mucous membranes,
delayed capillary refill, and reduced skin turgor.
Other physical exam findings may give clues
to the etiology of diarrhea.
Examples include rashes and joint pain that
can accompany inflammatory bowel disease, distention
and peritoneal signs indicating a surgical abdominal process,
palpable stool associated with anco precis,
or even acute otitis media, which can have an associated
diarrhea in young children.
Diagnosis.
Taking a careful history is the most important step
in narrowing down what is a very large initial differential,
starting with the chronicity of the diarrhea.
Acute episodes are considered to be less than 2 weeks,
and chronic diarrhea is greater than 4 weeks in duration.
Age, recent travel history, sick contacts,
a history of recent antibiotic use,
initiation of a new medication, and evidence
of immunodeficiency, or systemic illness.
Color and consistency are two important factors
to consider when creating a differential
diagnosis for any concern related
to stool, not just diarrhea.
Troubling colors include red and black,
which could indicate a lower versus upper GI bleed,
respectively.
And white, indicating a hepatobiliary source.
Bloody diarrhea may be due to infection, ischemia, allergy,
or immune mediated inflammation, such as inflammatory bowel
disease, or IBD.
Foul smelling, or floating stools,
or the presence of mucus, fat, and/or undigested food
particles, can all suggest malabsorption.
Diarrhea associated with low grade fevers,
vomiting, and/or respiratory symptoms,
are more consistent with viral causes of acute diarrhea.
In places where the rotaviris vaccine is available,
norovirus is now the leading cause of viral gastroenteritis
in children.
If there is concern for a bacterial infection,
providers should consider pursuing
a more extensive workup, starting
with stool cultures for Salmonella, Shigella,
Campylobacter, Yersinia, and Shiga toxin producing E. coli.
Clostridium difficile testing should also
be considered as community acquired
infections are increasing, especially if there
is recent antibiotic use.
Children under the age of 2 may be asymptomatic carriers,
so testing should be performed after careful consideration.
Children who have traveled or in endemic areas
should have their stool tested for ova and parasites.
The results of these tests will inform
treatment not covered here.
If a child with acute diarrhea is ill appearing,
the workup is more extensive.
In addition to stool cultures, this
may include a basic metabolic panel,
electrolytes including rapid glucose, BUN, and creatinine.
A complete blood count including differential,
a peripheral blood smear to assess
for hemolytic uremic syndrome, and a blood culture.
Plain abdominal radiographs are only
necessary in patients with suspicion of toxic megacolon,
peritonitis, or perforation.
An ultrasound may be performed to rule out intussusception
or appendicitis.
Chronic causes of diarrhea should
be thought about differently.
A history of weight loss or blood in the stool
should prompt a workup for IBD, which likely includes bloodwork
for inflammatory markers, such as C-reactive protein,
stool studies such as fecal calprotectin or lactoferrin,
markers for neutrophil activity, colonoscopy,
and abdominal imaging.
Weight loss can also be an early sign
of celiac disease, for which tissue transglutaminase
immunoglobulin antibody testing should be obtained.
Celiac disease is also on the differential
for patients suspected of malabsorption
along with lactase deficiency, pancreatic insufficiency,
and post-infectious diarrhea that can occur due to villus
atrophy from mucosal injury.
Much more rarely, chronic diarrhea
can be caused by motility disorders, hyperthyroidism,
immunodeficiency syndromes, or neuroendocrine tumors,
and is seen in neonates or infants,
congenital enteropathies.
Diarrhea that does not reveal an organic cause on workup,
meaning there is not an identifiable anatomic,
chemical, or biological cause, is referred
to as functional diarrhea.
This is extremely common.
In children less than five, this is
called chronic non-specific diarrhea or toddler's diarrhea,
which can be due to overfeeding, excessive formula intake,
and/or a diet high in fruit juice, or sorbitol.
In children over 5, one of the most common functional
diarrheas is diarrhea-predominant irritable
bowel syndrome, or IBS.
This can be diagnosed with the Rome IV
criteria, which includes an association
with abdominal pain.
Management.
Management of diarrhea depends on
whether the diarrhea is acute or chronic.
For acute diarrhea, management is supportive and focuses
particularly on rehydration.
For chronic diarrhea, management depends
on treating the underlying cause, if known or possible.
Most commonly, children with diarrhea
can be managed with supportive care in the outpatient setting.
If it is an acute episode of diarrhea,
such as gastroenteritis, they can
be managed with oral rehydration solution
to preserve hydration status.
The World Health Organization oral rehydration solution
is hypo-osmolar with optimized glucose to sodium ratios
to increase water absorption through the sodium glucose
co-transporter, SGLT1, and sodium-coupled amino acid
transporters.
Admission for rehydration should be considered
for children with electrolyte abnormalities,
lack of improvement with rehydration,
inability to drink, or suspicion for systemic illnesses
such as hemolytic uremic syndrome.
A trial of fasting can be considered
for suspected osmotic or diet induced diarrhea,
but otherwise a normal diet should be resumed
as soon as it is tolerable.
Antimotility agents such as loperamide
are not recommended in children.
Antiemetics such as ondansetron can
be used in children older than six months with nausea
and vomiting, but should be used cautiously
in anyone with electrolyte abnormalities,
or who are otherwise at risk for cardiac arrhythmias,
given the potential for QT prolongation.
The effectiveness of probiotics is controversial,
but there's evidence that certain commensal species may
help in antibiotic associated diarrhea, IBS,
or acute infectious diarrhea.
Summary.
In summary, diarrhea is an extremely common,
chief complaint in the pediatric world.
In resource rich settings, diarrhea
is rarely life threatening.
But if it is severe or occurs in a patient
from a vulnerable population, it should be investigated.
A thorough history and physical exam
will help narrow down a large differential,
but most acute cases can be managed without further testing
in an outpatient setting.
Thank you for watching this video on diarrhea.