What conditions are associated with a biopsy showing periodic acid‑Schiff (PAS) positive staining?

Conditions Associated with Periodic Acid-Schiff (PAS) Positive Biopsy Staining

PAS-positive staining on biopsy is most commonly associated with glycogen storage diseases (types I-IX), pulmonary alveolar proteinosis, and fungal infections, with the specific pattern and diastase sensitivity helping distinguish between these entities.

Primary Diagnostic Categories

Glycogen Storage Diseases

The most comprehensive diagnostic framework comes from glycogen storage disease guidelines 1:

PAS-positive cytoplasmic glycogen patterns:

• GSD Type I: PAS-positive cytoplasmic glycogen with significant lipid accumulation (diastase sensitive)
• GSD Type II (Pompe): PAS-positive vacuolated membrane-bound lysosomal glycogen
• GSD Type III: PAS-positive cytoplasmic glycogen mixed with some lipid accumulation (diastase sensitive, structurally abnormal with shorter outer branches)
• GSD Type IV: PAS-positive/diastase resistant amylopectin-like cytoplasmic glycogen (critical distinguishing feature)
• GSD Types V, VI, VII, IX: All show PAS-positive cytoplasmic glycogen

Key distinguishing feature: Diastase sensitivity differentiates most GSDs from Type IV, where the abnormal amylopectin-like glycogen resists diastase digestion 1.

Pulmonary Alveolar Proteinosis (PAP)

The 2024 European Respiratory Society guidelines provide the most current diagnostic approach 2:

Diagnostic findings in bronchoalveolar lavage (BAL):

• PAS-positive granular material with hypocellularity is diagnostic
• Foamy macrophages containing eosinophilic granules and amorphic material that stains PAS-positive
• Tubular myelin-like lamellar bodies on electron microscopy
• BAL has 90.7% diagnostic yield for PAP 2

The 2024 guidelines strongly recommend BAL with PAS staining as part of the diagnostic workup for suspected PAP, given its high yield and low risk 2.

Fungal Infections

Multiple guidelines address PAS staining for fungal identification 3, 4:

Fungal organisms demonstrate:

• PAS-positive staining of hyphal elements and yeast forms
• Characteristic acute angle branching septate hyphae for Aspergillus species
• Special stains (GMS, PAS) should be performed simultaneously when fungal infection is suspected 3

Clinical context matters: In dermatoses of palms and soles, routine PAS has only 3% positivity rate, increasing to 6% when tinea is clinically suspected 5. The yield improves when limited to non-specific reaction patterns 5.

Childhood Interstitial Lung Disease

The 2013 American Thoracic Society guidelines identify specific BAL findings 6:

Diagnostic BAL findings:

• PAS-positive granular material with hypocellularity suggests alveolar proteinosis (consider surfactant dysfunction mutations or GM-CSF-related disorders)
• This finding should prompt investigation for surfactant dysfunction mutations, GM-CSF pathway abnormalities, and lysinuric protein intolerance

Other Conditions with PAS Positivity

Whipple's Disease:

• Classic presentation shows PAS-positive foamy macrophages in duodenal biopsy
• Important caveat: PAS-negative noncaseating granulomas can occur in lymph nodes while still harboring Whipple bacilli (demonstrated only by electron microscopy) 7

Hereditary Diffuse Gastric Cancer (CDH1 mutations):

• PAS staining is superior to H&E for detecting invasive signet-ring adenocarcinoma in prophylactic gastrectomy specimens
• Reduces screening time by approximately 2 hours while improving detection rates 8

Lymphoblastic Leukemia:

• Strong PAS positivity (>10% blast cells) occurs in 25% of childhood ALL cases
• Associated with "common" ALL immunophenotype and blast cell vacuoles
• Predicts better treatment response 9

Practical Diagnostic Algorithm

When encountering PAS-positive material:

1. Assess diastase sensitivity

   • Diastase-sensitive → Consider GSDs I, II, III, V, VI, VII, IX or glycogen accumulation
   • Diastase-resistant → Consider GSD IV or fungal organisms

2. Evaluate tissue context

   • Liver/muscle biopsy → Glycogen storage diseases
   • BAL fluid → Pulmonary alveolar proteinosis or fungal infection
   • Duodenal biopsy → Whipple's disease
   • Gastric mucosa → Signet-ring adenocarcinoma (in CDH1 carriers)
   • Bone marrow → Lymphoblastic leukemia

3. Examine staining pattern

   • Cytoplasmic glycogen → Most GSDs
   • Membrane-bound vacuoles → GSD II (Pompe)
   • Granular material with hypocellularity → PAP
   • Hyphal/yeast forms → Fungal infection

4. Correlate with clinical presentation

   • Hepatomegaly, hypoglycemia → GSDs
   • Respiratory symptoms, "crazy paving" on CT → PAP
   • Malabsorption, arthralgia → Whipple's disease

Critical Pitfalls to Avoid

• Do not rely on PAS alone for fungal diagnosis: Culture or molecular confirmation is necessary to distinguish Aspergillus from other filamentous fungi like Fusarium or Scedosporium 3
• Fixation matters: For optimal glycogen demonstration, use 10% neutral buffered formalin or 80% alcohol; Bouin's solution works only at 4°C 10
• PAS-negative does not exclude disease: Whipple's disease can present with PAS-negative granulomas that still contain bacilli 7
• Consider structural glycogen abnormalities: GSD III shows decreased glucose-1-phosphate to glucose ratio, distinguishing it from other GSDs 1