Cystic Fibrosis

Overview

Hereditary disorder — VISCID mucous secretions in ALL exocrine glands (“mucoviscidosis”), + ↑electrolytes in eccrine(sweat) glands. Name preference: “cystic fibrosis”/“fibrocystic disease” > “mucoviscidosis” — because main lesion = FIBROSIS from obstruction, not the mucus itself (mucus = initiating mechanism only).

Genetics

AUTOSOMAL RECESSIVE, clinical features only in HOMOZYGOTES. Defect = CFTR gene mutation (chr7). Common in Whites (1/2000 livebirths). Manifests birth→adolescence. Multi-organ: pancreatic insufficiency, intestinal obstruction, steatorrhoea, malnutrition, hepatic cirrhosis, respiratory complications.

Morphology by organ (unified mechanism: obstruction by viscid mucus)

1. Pancreas — almost invariably involved. Gross: lobules OVOID not rhomboid (contrast normal), fatty replacement, ±visible cysts. Micro: lobular architecture PRESERVED; ↑interlobular fibrosis; atrophic acini; LAMINATED EOSINOPHILIC CONCRETIONS in ducts; ±inflammation/fat necrosis/cysts. ISLET TISSUE (endocrine) GENERALLY SPARED (key distinguishing fact — glucose tolerance retained longer than exocrine insufficiency suggests). Exocrine atrophy→impaired fat absorption, steatorrhoea, intestinal obstruction, vitamin A deficiency.

2. Liver — bile canaliculi plugged by mucus→fatty change, portal fibrosis, ductular proliferation. Severe→BILIARY CIRRHOSIS.

3. Respiratory tract — seen in almost ALL typical cases. Viscid submucosal secretions→obstruction/dilatation/infection: chronic bronchitis, bronchiectasis, bronchiolitis, bronchiolectasis, peribronchiolar pneumonia, inflammatory nasal polyps.

4. Salivary glands — parallels pancreas: ductal obstruction, dilatation, fibrosis, atrophy.

5. Sweat glands — DIAGNOSTIC OUTLIER: pathology = electrolyte-concentration abnormality(↑Na/Cl in sweat), NOT viscid-secretion obstruction like other organs. Reflected as diminished eccrine cell vacuolation. Basis for SWEAT CHLORIDE TEST (clinical diagnosis).

Clinical relevance

Islet sparing amid severe exocrine destruction = key fact — glucose tolerance retained longer than steatorrhoea/malabsorption would suggest. Naming rationale states the primary lesion directly: fibrosis(obstruction-driven), not mucus abnormality itself. Multi-organ pattern unified by ONE mechanism(viscid secretion obstruction) — organising principle, not 5 separate disease processes. Sweat gland = the exception(electrolyte abnormality, not obstruction) — basis for the sweat chloride diagnostic test.

Overview

Cystic fibrosis (fibrocystic disease) is a hereditary disorder producing viscid mucous secretions in all exocrine glands of the body (“mucoviscidosis”), with increased electrolyte concentrations in the eccrine (sweat) glands. The terms “cystic fibrosis”/“fibrocystic disease” are preferred over “mucoviscidosis” because the main pathologic change is fibrosis resulting from passage obstruction by the viscid mucus, rather than the mucus itself being the defining lesion.

Genetics

Autosomal recessive inheritance; clinical features apparent only in homozygotes. The defect is a genetic mutation in the CFTR gene (cystic fibrosis transmembrane conductance regulator) on chromosome 7. Fairly common in White populations (1 per 2000 livebirths). Clinical manifestations may appear at birth or later in adolescence, involving multiple organs/systems: pancreatic insufficiency, intestinal obstruction, steatorrhoea, malnutrition, hepatic cirrhosis, and respiratory complications.

Morphology by Organ

Pathologic severity/pattern varies by organ, but most changes trace back to obstruction by viscid mucus.

1. Pancreas

Almost invariably involved. Gross: lobules are ovoid rather than rhomboid (contrast with normal); fatty replacement; grossly visible cysts. Micro: lobular architecture is preserved; increased interlobular fibrosis; atrophic acini; many acinar ducts contain laminated eosinophilic concretions; occasionally inflammation, fat necrosis, cyst formation. The islet tissue (endocrine pancreas) is generally spared. Exocrine atrophy causes impaired fat absorption, steatorrhoea, intestinal obstruction, and vitamin A deficiency.

2. Liver

Bile canaliculi plugged by viscid mucus → diffuse fatty change, portal fibrosis, ductular proliferation. More severe involvement can progress to biliary cirrhosis.

3. Respiratory Tract

Changes are seen in almost all typical cases. Viscid submucosal-gland secretions cause airway obstruction, dilatation, and infection: chronic bronchitis, bronchiectasis, bronchiolitis, bronchiolectasis, peribronchiolar pneumonia, inflammatory nasal polyps.

4. Salivary Glands

Pathologic changes parallel the pancreas: ductal obstruction, dilatation, fibrosis, glandular atrophy.

5. Sweat Glands

Hypersecretion of sodium and chloride in sweat — reflected pathologically as diminished vacuolation of eccrine gland cells.

Clinical Relevance

The islet (endocrine pancreas) sparing amid otherwise severe exocrine pancreatic destruction is a genuinely important distinguishing fact — cystic fibrosis patients characteristically retain glucose tolerance longer than the exocrine insufficiency (steatorrhoea, malabsorption) would otherwise suggest, precisely because the endocrine tissue is relatively protected.
The naming rationale — “cystic fibrosis”/“fibrocystic disease” over “mucoviscidosis” — is worth remembering as a direct statement about what the primary pathologic lesion actually is: obstruction-driven fibrosis, not the mucus abnormality itself, which is only the initiating mechanism.
The multi-organ pattern (pancreas, liver, respiratory tract, salivary glands, sweat glands) is unified by one single mechanism — exocrine gland secretion becoming too viscid to drain normally — worth using as the organising principle rather than memorising five separate organ-specific disease processes.
Sweat gland involvement is the diagnostic outlier in this list: unlike the other organs, the pathologic change here is an electrolyte-concentration abnormality (not viscid-secretion obstruction), and this is precisely the basis for the sweat chloride test used clinically to diagnose cystic fibrosis.

Central “viscid mucus obstruction” mechanism radiating out to its five organ-specific consequences (pancreas, liver, respiratory tract, salivary glands) with sweat glands marked as the electrolyte-based exception