Cystic Fibrosis

Slide 1 · Cystic Fibrosis

Malabsorption and gastrointestinal pathology

An epithelial ion-transport disorder with pancreatic, intestinal and hepatobiliary consequences

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Mechanism

Explain how defective CFTR alters epithelial electrolyte and water movement.

Morphology

Recognize the sequence from ductal concretions to pancreatic fibrosis.

Function

Relate loss of digestive enzymes to steatorrhea and deficiencies.

Application

Differentiate intestinal obstruction and pancreatic phenotypes.

Slide 3 · Scope: Gastrointestinal consequences of cystic fibrosis

The gastrointestinal chapter treats cystic fibrosis principally as a cause of malabsorption.

Pulmonary disease is central to systemic cystic fibrosis, but is background in this lecture.

Pancreatic duct obstruction connects the genetic defect to defective intraluminal digestion.

Slide 4 · Where cystic fibrosis disrupts nutrient absorption

Intraluminal digestion

Pancreatic enzymes degrade nutrients; This is the principal CF-related defect.

Terminal digestion

Brush-border hydrolases complete carbohydrate and peptide digestion.

Transepithelial transport

Absorbed molecules cross intestinal epithelial cells.

Lymphatic transport

Absorbed lipids are transported away from the mucosa.

Slide 5 · A single inherited defect affects multiple organs

Defective

CFTR

Pancreas

Obstructed ducts → exocrine insufficiency

Intestine

Dehydrated contents → obstruction

Hepatobiliary tract

Mucus plugging → biliary injury

Airways

Impaired clearance → chronic infections

Sweat ducts

Reduced salt reabsorption → salty sweat

Slide 6 · CFTR is an epithelial anion channel

CFTR: Cystic fibrosis transmembrane conductance regulator.

The encoding gene lies on chromosome 7q31.2.

CFTR mediates chloride transport and contributes to bicarbonate transport.

The effect of CFTR dysfunction depends on epithelial tissue type.

Slide 7 · CFTR architecture supports regulated channel opening

Transmembrane domains

Two membrane-spanning domains form the anion-conducting pore.

Nucleotide-binding domains

ATP binding and hydrolysis regulate gating.

Regulatory domain

Protein kinase A phosphorylation facilitates channel opening.

Functional consequence

A defect can affect abundance, trafficking, gating or conductance.

Slide 8 · How a normally functioning CFTR channel opens

Agonist signal

Increased intracellular cAMP

Protein kinase A activation

R-domain phosphorylation

CFTR channel activity

Slide 9 · Healthy intestinal epithelial surface fluid

Normal epithelium

SCHEMATIC: LUMEN

Epithelium

CFTR

Fluid secretion

CFTR supports chloride secretion; Luminal surface fluid remains hydrated.

Cystic fibrosis

SCHEMATIC: LUMEN

Epithelium

CFTR

Reduced fluid

Reduced anion secretion and altered sodium handling reduce luminal water.

Slide 10 · Epithelial sodium transport amplifies water loss

Reduced CFTR inhibition of ENaC

Increased luminal sodium uptake

Passive water reabsorption

Decreased surface liquid volume

Slide 11 · Bicarbonate transport is especially important in ducts

CFTR conducts bicarbonate as well as chloride.

CFTR also interacts with SLC26-family apical anion exchangers.

Reduced bicarbonate delivery results in abnormally acidic secretions.

Acidic fluid favors mucin precipitation and duct plugging.

Slide 12 · The biochemical route to mucus precipitation

CFTR dysfunction

Reduced bicarbonate secretion

Lower luminal pH

Mucin precipitation

Ductal obstruction

Slide 13 · Chloride and bicarbonate defects have related effects

Transport defect

Pancreatic/GI consequence

Reduced chloride secretion

Less water maintained in the epithelial lumen

Reduced bicarbonate secretion

Acidic secretion and increased mucin precipitation

Combined ductal effect

Low-volume, poorly flowing, viscous secretions

Slide 14 · Why the pancreas is a vulnerable target

Secretory pancreatic ducts

Inadequate electrolyte-rich fluid

Concentrated intraductal secretions

Obstruction of the exocrine outflow

Slide 15 · From CFTR dysfunction to malabsorption

Defective CFTR

Thickened pancreatic secretions

Intraductal concretions

Pancreatic parenchymal loss

Deficient luminal enzymes

Slide 16 · Normal pancreatic outflow versus obstructed ducts

Patent duct

Schematic — simplified lumen

Aqueous pancreatic fluid carries enzymes into the intestine.

Obstructed duct

Schematic — simplified lumen

Viscous concretions impede flow and injure exocrine tissue.

Slide 17 · Pancreatic lesions may begin in utero

Intraductal concretions can start forming during fetal development.

Luminal obstruction may therefore predate postnatal symptoms.

Pancreatic damage accumulates before clinically apparent malabsorption.

Slide 18 · Initial pancreatic morphology: Retained mucus

Milder disease

Schematic — duct / surrounding tissue

Mucus accumulates in small ducts with variable gland dilation.

Progressive disease

Schematic — duct / surrounding tissue

Marked intraductal plugging leads to obstructive tissue injury.

Slide 19 · Duct obstruction produces chronic pancreatic injury

Intraductal material

Outflow obstruction

Low-grade chronic pancreatitis

Progressive exocrine damage

Slide 20 · Advanced pancreatic pathology

Plugging

Ducts are filled with viscous material.

Dilation

Obstructed ductal structures dilate.

Atrophy

Acinar tissue progressively disappears.

Fibrosis

Fibrofatty stroma replaces exocrine parenchyma.

Slide 21 · End-stage pancreas: Acini lost, islets relatively retained

Feature

Interpretation

Exocrine compartment

Widespread acinar destruction and fibrosis

Ductal compartment

Dilatation and persistent obstruction

Endocrine compartment

Islets can remain within fibrofatty stroma

Slide 22 · Microscopic pattern: An obstructive fibroatrophic process

Early pattern

Schematic — duct / surrounding tissue

Luminal mucus with duct dilation and residual acini.

Late pattern

Schematic — duct / surrounding tissue

Marked loss of exocrine parenchyma with fibrous replacement.

Slide 23 · How exocrine pancreatic insufficiency develops

Loss of exocrine acini

Reduced digestive enzyme output

Inadequate luminal hydrolysis

Nutrient maldigestion

Fecal nutrient loss

Slide 24 · Pancreatic insufficiency is common in classic CF

The gastrointestinal section reports exocrine pancreatic insufficiency in more than 80% of patients.

The systemic CF chapter describes pancreatic insufficiency in about 85%–90%.

A pancreatic-sufficient phenotype also occurs.

Severity reflects the functional consequences of the CFTR alleles.

Slide 25 · Defective intraluminal digestion is not a villous lesion

Disorder

Predominant mechanistic location

Cystic fibrosis

Pancreatic enzyme deficiency; Predominantly intraluminal digestion failure

Celiac disease

Intestinal mucosal disease with absorptive and digestive defects

Disaccharidase deficiency

Brush-border terminal digestion defect

Slide 26 · Normal fat handling requires pancreatic digestion

Dietary triglycerides

Pancreatic enzyme activity

Digestible lipid products

Intestinal absorption

Nutritional lipid delivery

Slide 27 · Why steatorrhea develops in CF

Insufficient pancreatic enzymes

Incomplete fat digestion

Unabsorbed intestinal lipids

Excess fecal fat

Bulky greasy stool

Slide 28 · Recognizing malabsorptive stools

Bulky and foul-smelling stools are characteristic of CF-associated malabsorption.

Stool may be greasy or frothy because of excessive fecal fat.

Abdominal distension and chronic diarrhea can accompany steatorrhea.

These findings indicate maldigestion; They are not individually specific for CF.

Slide 29 · Protein maldigestion adds nutritional loss

Low pancreatic protease delivery

Impaired luminal protein hydrolysis

Reduced nutrient acquisition

Protein malnutrition

Low plasma proteins

Slide 30 · Malabsorption links pancreas to impaired growth

Enzyme deficiency

Fecal loss of fat and protein

Insufficient nutrient retention

Poor weight gain

Impaired growth in childhood

Slide 31 · Fat-soluble vitamins are vulnerable

Vitamin A

Deficiency may affect epithelial integrity; Pancreatic duct metaplasia.

Vitamin D

Deficiency can contribute to osteopenia and disordered mineral homeostasis.

Vitamin E

Vitamin E belongs to the fat-soluble group at risk in malabsorption.

Vitamin K

Deficiency can lead to a bleeding tendency.

Slide 32 · Vitamin A: Duct epithelial consequences

Loss of exocrine secretion impairs absorption of fat-soluble nutrients.

Vitamin A deficiency may contribute to squamous metaplasia of pancreatic duct epithelium.

Duct lining cells already sustain damage from inspissated secretions.

Slide 33 · Vitamin D: Skeletal consequences of malabsorption

Chronic malabsorption can reduce absorption of vitamin D and minerals.

The Robbins malabsorption section associates these deficiencies with osteopenia and tetany.

Poor growth may coexist with skeletal and mineral consequences.

Slide 34 · Vitamin K deficiency can manifest as bleeding

Pancreatic fat maldigestion

Fat-soluble vitamin malabsorption

Vitamin K deficiency

Impaired hemostatic support

Bleeding tendency

Slide 35 · Clinical phenotype: Nutritional and GI manifestations

Stool

Large, greasy, foul-smelling stools; Persistent diarrhea.

Abdomen

Distension, flatus, discomfort and sometimes obstruction.

Growth

Poor weight gain, wasting and failure to thrive.

Systemic

Vitamin deficiency and, when severe, hypoproteinemic edema.

Slide 36 · Pancreatic and intestinal luminal problems are distinct

Site

Principal consequence

Pancreas

Obstructed ducts → parenchymal destruction → enzyme deficiency

Intestine

Viscous luminal contents → bowel obstruction in some patients

Clinical difference

Malabsorption predominates for pancreas; Obstruction is a separate intestinal event

Slide 37 · Viscous intestinal contents predispose to blockage

Reduced intestinal secretion

Less luminal water

Thickened intestinal contents

Impaired forward transit

Possible obstruction

Slide 38 · Meconium ileus: Neonatal obstruction

Thick, viscid meconium may obstruct the small intestine in affected newborns.

The systemic chapter reports presentation with meconium ileus in approximately 5%–10% of cases.

This can bring cystic fibrosis to clinical attention at or shortly after birth.

Slide 39 · Meconium ileus: Mechanism and anatomic pattern

Normal neonatal bowel

Schematic — simplified lumen

Meconium traverses an unobstructed intestinal lumen.

Cystic fibrosis

Schematic — simplified lumen

Inspissated meconium forms an obstructive luminal plug.

Slide 40 · Clinical exercise: Neonatal intestinal obstruction

Clinical reasoning exercise

A neonate develops early signs of intestinal obstruction.

The obstructing material is unusually thick meconium.

What inherited epithelial transport disease links this presentation to pancreatic insufficiency?

Slide 41 · Case reasoning: Meconium ileus points toward CF

CFTR dysfunction reduces epithelial fluid secretion into the intestine.

Inspissated meconium can obstruct the small bowel.

The same channel defect also drives pancreatic duct plugging and malabsorption.

Slide 42 · Distal intestinal obstruction syndrome in older patients

Distal intestinal obstruction may occur after infancy.

Recurrent right lower quadrant pain.

A palpable meconium-containing mass may occur in the right iliac fossa.

Intussusception may or may not accompany the episode.

Slide 43 · Meconium ileus versus distal intestinal obstruction

Feature

Meconium ileus

Distal intestinal obstruction

Typical period

Newborn / soon after birth

Older children or other individuals

Dominant problem

Early small-bowel obstruction

Recurrent distal intestinal obstruction

Clinical clues

Thick neonatal meconium

Right lower quadrant pain ± palpable mass

Slide 44 · Rectal prolapse may complicate chronic diarrhea

Pancreatic maldigestion

Persistent malabsorptive diarrhea

Recurrent straining / increased stool burden

Rectal prolapse in some children

Slide 45 · Pancreatic sufficiency is a real CF phenotype

Phenotype

Exocrine consequence

Pancreatic insufficient

Defective enzyme delivery → malabsorption and enzyme-replacement need

Pancreatic sufficient

Enough residual exocrine function to avoid routine enzyme replacement

Slide 46 · Why some mutations spare pancreatic function

Residual CFTR activity

Better maintained duct fluid

Less severe obstruction

Preserved acinar function

Pancreatic sufficiency

Slide 47 · Pancreatic-sufficient CF can present with pancreatitis

Some pancreas-sufficient patients have recurrent acute pancreatitis.

Episodes can include acute abdominal pain and severe complications.

Late-onset apparently idiopathic pancreatitis may reveal CFTR-related disease.

Thus pancreatic sufficiency and pancreatic inflammation can coexist.

Slide 48 · CFTR-associated pancreatitis can appear outside classic CF

Some idiopathic chronic pancreatitis to biallelic CFTR variants.

Other classic organ-system findings may be absent.

The pancreatic chapter also discusses CFTR-related pancreatitis susceptibility in heterozygous carriers.

Variant interpretation and broader clinical context therefore matter.

Slide 49 · Genotype–phenotype correlation is strongest in pancreas

Organ system

Predictability

Pancreas

Residual CFTR function predicts pancreatic sufficiency comparatively well.

Lung

Infection and modifier genes produce less consistent genotype prediction.

Clinical implication

Do not extrapolate pancreatic severity to all other organs.

Slide 50 · Six broad mechanisms of CFTR protein dysfunction

Class

Molecular mechanism

Functional result

I

Defective protein synthesis

Little or no functional channel

II

Folding / trafficking abnormality

Protein fails to reach surface

III

Defective gating

Surface channel fails to open properly

IV

Reduced ionic conductance

Ion movement through channel impaired

V

Reduced protein abundance

Less otherwise functional channel

VI

Reduced surface stability

Shorter lifetime of membrane CFTR

Slide 51 · Phe508del exemplifies defective CFTR processing

Deletion of phenylalanine 508

Abnormal folding / maturation

Premature cellular degradation

Reduced apical CFTR

Severe duct secretory failure

Slide 52 · Pancreatic severity reflects remaining CFTR function

Severe alleles

Very limited apical channel function.

Ductal consequence

Poor bicarbonate-rich fluid secretion.

Pancreatic consequence

Mucus plugging and progressive exocrine loss.

Functional outcome

Pancreatic insufficiency and malabsorption.

Slide 53 · Hepatobiliary changes use the same obstructive logic

Abnormal biliary secretions

Plugged small bile channels

Ductular reaction

Portal inflammation

Focal biliary fibrosis / cirrhosis

Slide 54 · Histologic liver pattern in cystic fibrosis

Biliary mucus accumulation and plugging are described.

Ductular proliferation accompanies portal inflammation.

Steatosis may also occur.

Progressive involvement can produce focal biliary cirrhosis and, rarely, diffuse nodularity.

Slide 55 · Clinical liver disease may emerge later

Hepatobiliary disease becomes increasingly relevant with longer survival.

Symptomatic or biochemical involvement often around puberty.

Common bile duct sludge or stones can cause pain with acute jaundice.

Diffuse biliary cirrhosis is reported in fewer than 10% of affected individuals.

Slide 56 · Salivary ducts demonstrate the shared exocrine pattern

Viscous secretions

Secretory material accumulates.

Ductal change

Duct lumens progressively dilate.

Epithelium

Squamous metaplasia may develop.

Parenchyma

Gland atrophy progresses toward fibrosis.

Slide 57 · Sweat and intestinal epithelia behave differently

Epithelial site

Effect of CFTR dysfunction

Sweat gland duct

Reduced NaCl reabsorption → elevated sweat electrolyte concentration

Intestinal and airway epithelium

Reduced luminal anion secretion → depleted surface fluid

Lesson

CFTR loss affects ion transport differently by tissue

Slide 58 · Malabsorptive diarrhea versus other diarrhea types

Pattern

Mechanism

Distinguishing observation

Malabsorptive

Impaired nutrient absorption, often steatorrhea

Common with pancreatic insufficiency

Osmotic

Unabsorbed solutes retain luminal fluid

Classically improves with fasting

Secretory

Ongoing epithelial fluid secretion

Often persists during fasting

Exudative

Inflammatory mucosal injury

May include purulent or bloody stool

Slide 59 · GI differential: Pancreatic failure versus mucosal disease

Candidate process

Where dysfunction arises

CF-associated pancreatic insufficiency

Reduced luminal enzyme delivery to the gut

Celiac disease

Gluten-triggered immune-mediated small-intestinal pathology

Crohn disease

Chronic inflammatory disease can produce malabsorption

Slide 60 · The diagnostic clue is a multisystem pattern

Defective

CFTR

GI

Steatorrhea, poor growth, obstruction

Pancreas

Exocrine insufficiency or recurrent pancreatitis

Respiratory

Chronic cough, infections, bronchiectasis

Sweat

Elevated electrolyte concentrations

Family

Consistent recessive history or sibling diagnosis

Slide 61 · Newborn screening is a starting point, not final diagnosis

A common newborn screening approach measures immunoreactive trypsinogen.

Elevated levels reflect pancreatic injury.

A positive newborn screen requires appropriate confirmatory evaluation.

Pancreatic manifestations may provide the first clinical evidence of CF.

Slide 62 · Sweat testing exploits tissue-specific CFTR physiology

CFTR defect in sweat duct

Reduced chloride reclamation

Reduced sodium chloride reabsorption

Elevated sweat chloride

Support for CF diagnosis

Slide 63 · Clinical features must be integrated with CFTR evidence

Clinical phenotype / positive screening

Sweat chloride evaluation

CFTR variant assessment

Functional epithelial testing if needed

Slide 64 · Diagnostic interpretation requires caution

Classic cystic fibrosis has characteristic manifestations and demonstrable CFTR dysfunction.

Milder alleles may be associated with less typical clinical presentations.

Sweat results may be normal or near-normal in a minority of atypical cases.

Physiological testing and genetic interpretation can be complementary.

Slide 65 · Pancreatic enzyme replacement targets the failed step

Insufficient pancreatic exocrine output

Oral digestive enzyme replacement

Improved intraluminal nutrient breakdown

Potential improvement in absorption

Slide 66 · Mutation-directed therapies target upstream CFTR biology

Potentiators

Improve channel opening and function of suitable CFTR variants.

Correctors

Improve folding and trafficking of some defective CFTR proteins.

Amplifiers

Increase CFTR protein production; Discussed as a mechanistic class.

Enzyme therapy

Replaces downstream digestive function rather than correcting CFTR.

Slide 67 · Therapeutic targets lie at different points in the cascade

Mutant CFTR protein

Abnormal duct fluid chemistry

Pancreatic injury

Reduced enzymes

Malabsorption

Slide 68 · Application: Interpreting a malabsorptive phenotype

Clinical reasoning exercise

A child has large greasy stools, poor weight gain and recurrent respiratory symptoms.

Pancreatic exocrine function is markedly reduced.

Which of the four phases of nutrient absorption is primarily disrupted?

Slide 69 · Case reasoning: Failure occurs before mucosal uptake

CFTR dysfunction causes pancreatic ductal concretions and injury.

Loss of pancreatic exocrine tissue lowers enzyme delivery.

Intraluminal digestion fails; Unprocessed nutrients remain in stool.

A primary enterocyte transport defect is not required to explain this presentation.

Slide 70 · Application: Pancreatitis without obvious steatorrhea

Clinical reasoning exercise

An individual with CFTR-related disease has repeated episodes of pancreatitis.

Growth is preserved and enzyme replacement is not needed.

Why can pancreatitis coexist with preserved exocrine output?

Slide 71 · Case reasoning: Residual function can preserve digestion

Residual CFTR function may protect much of the exocrine pancreas.

Duct secretion can still be abnormal enough to predispose to pancreatitis.

Pancreatic sufficiency therefore does not exclude CFTR-related pancreatic disease.

Slide 72 · Common conceptual errors in cystic fibrosis malabsorption

Incorrect inference

Correct interpretation

“All CF causes pancreatic insufficiency.”

A pancreatic-sufficient phenotype is documented.

“The intestinal villi are the primary lesion.”

The principal CF malabsorptive defect is intraluminal digestion.

“Salty sweat means all lumens are hypertonic.”

Sweat ducts and intestinal epithelia have different CFTR roles.

“Enzyme therapy fixes the gene defect.”

Enzymes replace digestive function downstream of CFTR.

Slide 73 · Integrated pathological mechanism

CFTR ion transport defect

Reduced fluid / bicarbonate secretion

Ductal plugs and chronic injury

Exocrine enzyme deficiency

Maldigestion and malabsorption

Slide 74 · Core findings to retain

Primary lesion

Defective CFTR-mediated epithelial ion transport.

Pancreatic morphology

Ductal concretions, exocrine atrophy and fibrosis.

GI physiology

Impaired intraluminal digestion with steatorrhea.

Clinicopathology

Malnutrition; Possible meconium ileus, distal obstruction and biliary disease.

Slide 75 · Primary textbook references

*Robbins, Cotran & Kumar: Pathologic Basis of Disease*, 11th ed. (2026).

The Gastrointestinal Tract — Malabsorption and Diarrhea: Cystic Fibrosis.

Diseases of Infancy and Childhood — Cystic Fibrosis (Mucoviscidosis).

The Pancreas — sections discussing CFTR-associated pancreatic injury.