Which of the following pathological changes in pancreatic islet architecture is most characteristic of Type 2 Diabetes Mellitus?

Explanation

## Pathological Changes in Type 2 Diabetes Mellitus ### Islet Amyloid Deposition — The Hallmark Feature **Key Point:** Type 2 DM is characterized by islet amyloid polypeptide (IAPP, also called amylin) deposition within pancreatic islets, leading to progressive beta cell dysfunction and loss. ### Composition and Origin of Islet Amyloid 1. **IAPP — the primary amyloidogenic protein** - A 37-amino acid peptide co-secreted with insulin by beta cells - Normally soluble and physiologically active (regulates gastric emptying, satiety) - In T2DM, IAPP misfolds and polymerizes into amyloid fibrils 2. **Mechanism of amyloid formation** - Chronic hyperglycemia and hyperinsulinemia promote IAPP aggregation - Impaired proteolytic degradation of misfolded IAPP - Accumulation of amyloid fibrils within islet tissue ### Histopathological Features of T2DM Islets | Feature | Pathology | Consequence | | --- | --- | --- | | **Amyloid deposition** | Extracellular IAPP fibrils in islet core | Progressive beta cell apoptosis | | **Beta cell loss** | 20–50% reduction in beta cell mass | Insufficient insulin secretion | | **Preserved architecture** | Islets remain identifiable (unlike T1DM) | No insulitis or lymphocytic infiltration | | **Fibrosis** | Mild to moderate interstitial fibrosis | Impaired islet vascularization | | **Hyalinization** | Amyloid deposits appear as eosinophilic material | Visible on H&E staining | **High-Yield:** IAPP amyloid deposition is found in ~90% of Type 2 DM pancreata at autopsy, making it the most consistent pathological hallmark of the disease. ### Distinction from Type 1 DM | Feature | Type 1 DM | Type 2 DM | | --- | --- | --- | | **Infiltrate** | CD8+ T cells (insulitis) | Absent | | **Amyloid** | Absent | Present (IAPP) | | **Beta cell loss** | 80–90% at diagnosis | 20–50% progressive | | **Islet structure** | Disrupted | Preserved | | **Mechanism** | Autoimmune | Metabolic/genetic | **Clinical Pearl:** IAPP amyloid toxicity contributes to beta cell apoptosis through multiple mechanisms: direct cytotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, and impaired autophagy. This explains why T2DM is progressive despite residual beta cell function. **Mnemonic:** **IAPP** = **I**slet **A**myloid **P**olypeptide **P**roduct — the pathological hallmark of Type 2 DM. [cite:Robbins 10e Ch 24]