Page 24 of 24

PA1.1-3,PA2.1-8 | Cell Injury, Adaptation & Cell Death — PBL Case

CLINICAL SETTING

Kamala, a 62-year-old woman from a village near Vellore, is brought to the surgery outpatient department of the district hospital by her daughter. She has had poorly controlled type 2 diabetes for 14 years and takes metformin irregularly. Three weeks ago she noticed a small blister on the sole of her right foot after walking barefoot in the fields. The blister burst, became wet and foul-smelling, and despite application of turmeric paste the wound has expanded to involve the entire forefoot. Today the forefoot is black and necrotic with foul-smelling discharge; the mid-foot is swollen, erythematous, and warm with a clear line separating dead from living tissue. Her blood glucose is 340 mg/dL and WBC is 18,400 cells/µL. The surgical resident suspects she will need an amputation, but the intern asks: what exactly has killed the cells in Kamala's foot, and why couldn't they adapt or recover?

Trigger 1: The Wound That Would Not Stop

The intern reviews Kamala's history more carefully. She has had a chronic non-healing ulcer on the sole for six months — initially painless (neuropathy), then progressively deepening. A week before the current admission, the wound margin turned greenish-black and dry on one side and swollen with pus-filled blisters on the other. The resident draws two circles on a sketch: one labelled 'dry black' and one labelled 'wet, swollen, draining pus'. He asks the intern to explain the difference in terms of what the cells are going through in each zone. The surgical pathologist who visits the ward notes that both zones will show cell death, but by different mechanisms and with different morphological appearances.

DISCUSSION POINTS

What are the primary causes of cell injury in Kamala's foot? Consider ischaemia (macrovascular and microvascular disease), infection, and metabolic derangement — how do these interact?
The dry black zone and the wet swollen zone show different gross appearances. What types of cell necrosis are most likely in each zone, and what underlying mechanism explains the difference?
At the biochemical level, how does ATP depletion in an ischaemic cell lead to the sequence: cellular swelling → membrane damage → irreversible injury? Which event marks the 'point of no return'?
The intern notes the ulcer was painless for months before this crisis. Which cellular adaptation or change in innervation explains this painlessness, and how might that adaptation itself have predisposed to deeper injury?

Click to reveal Trigger 2: Biopsy from the Border Zone (discuss previous trigger first!)

Trigger 2: Biopsy from the Border Zone

The surgeon performs a guillotine amputation at the ankle. Tissue is sent to the histopathology laboratory. The pathologist examines three sections: (A) from the black necrotic forefoot, (B) from the erythematous border zone, and (C) from the macroscopically normal calf skin. In section A she sees ghost outlines of tissue with eosinophilic homogenised cytoplasm, preserved architecture, and absent nuclei. In section B she sees a mixture — some cells with pale vacuolated cytoplasm and intact nuclei, others with pyknotic and karyorrhectic nuclei, and scattered neutrophils between dead adipocytes showing chalky deposits. In section C she sees small, shrunken muscle fibres with intact nuclei and a slight increase in fibrous tissue around them.

DISCUSSION POINTS

Section A shows preserved tissue architecture with eosinophilic ghost cells and absent nuclei. What specific type of necrosis is this, what is its hallmark mechanism, and why does architecture remain intact?
Section B shows chalky deposits within necrotic adipocytes. What is this process called, what biochemical reaction produces the deposits, and is the patient's calcium metabolism likely to be normal or abnormal?
The nuclear sequence in dying cells follows pyknosis → karyorrhexis → karyolysis. Arrange these in the correct order and explain the biochemical process driving each step.
Section C from the calf shows small shrunken muscle fibres with preserved cell number. The patient has been largely immobile for months. Name this adaptation, describe the intracellular degradation pathways responsible, and explain why it is considered reversible.

Click to reveal Trigger 3: Downstream and Upstream — Systemic Clues (discuss previous trigger first!)

Trigger 3: Downstream and Upstream — Systemic Clues

Post-operatively, the pathology team reviews Kamala's full medical record to understand the systemic context. Her liver function tests show mildly elevated ALT and AST. A liver biopsy taken during an unrelated laparoscopic procedure three years ago (before her diabetes was well-recognised) shows hepatocytes with large clear cytoplasmic vacuoles displacing the nuclei to the periphery, positive on frozen-section staining for lipid. A repeat biopsy now shows the same pattern plus scattered eosinophilic cytoplasmic inclusions in periportal hepatocytes. Her renal ultrasound reveals bilateral enlarged kidneys with echogenic cortices; her serum calcium is normal but PTH is mildly elevated. The intern is asked to synthesise: what do the liver findings, the renal findings, and the now-healed amputation stump tell us about the relationship between chronic metabolic stress and cell-level change?

DISCUSSION POINTS

The liver biopsy shows large clear vacuoles displacing the nucleus. What substance has accumulated, what metabolic imbalance in diabetes drives this, and how do you distinguish it from hydropic swelling on routine H&E?
The second biopsy shows eosinophilic cytoplasmic inclusions in periportal hepatocytes on a background of steatosis. What are the likely inclusions, and what do they tell you about the progression from reversible accumulation to more serious hepatocyte injury?
Kamala has diabetic nephropathy. The thickened glomerular basement membrane and mesangial expansion seen on the renal biopsy represent which cellular or extracellular adaptation? How does chronic hyperglycaemia drive non-enzymatic glycosylation of basement membrane proteins?
Considering the entire case — neuropathy, microangiopathy, macroangiopathy, hepatic steatosis, renal changes, and the final gangrenous foot — construct a unified cellular pathology narrative linking the repeated sublethal stress of chronic hyperglycaemia to the spectrum from adaptation through irreversible injury and death.

Group Task Assignments

Group 1: Cell injury mechanisms and the reversible–irreversible transition

Draw a flow diagram starting from ischaemia → ATP depletion → failure of Na⁺/K⁺-ATPase → cellular swelling, then branch to the two outcomes: restoration (reversible) vs continued depletion → calcium influx → membrane phospholipid breakdown → irreversible injury. Annotate each step with the biochemical mediator and the morphological change it produces.
Prepare a 5-minute presentation explaining why Kamala's black forefoot shows coagulative necrosis rather than liquefactive necrosis, and under what circumstances the same ischaemic limb could show liquefactive necrosis.

Competencies: PA2.1, PA2.2

Group 2: Types of necrosis and their morphological recognition

Create a side-by-side comparison table of all six types of necrosis (coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous) covering: typical organ/disease, gross appearance, microscopic appearance, and whether architecture is preserved or destroyed.
Using the histology images from the practical, identify and label: ghost cells of coagulative necrosis, pyknotic and karyorrhectic nuclei, chalky saponification deposits in fat necrosis, and neutrophil infiltrate — and relate each finding to Kamala's case.

Competencies: PA2.4, PA2.5, PA2.8

Group 3: Apoptosis vs necrosis and intracellular accumulations

Construct a comparison table of necrosis vs apoptosis covering: stimulus type, energy requirement, cell volume change, membrane integrity, nuclear changes, inflammatory response, and two clinical examples for each. Identify which process is occurring in Kamala's forefoot and which might be occurring in her hepatocytes.
Explain the metabolic pathway by which chronic hyperglycaemia leads to hepatic steatosis (lipid accumulation). Describe how this differs from the protein accumulations (Mallory–Denk bodies) on Kamala's second biopsy.

Competencies: PA2.3, PA2.4, PA2.7

Group 4: Cellular adaptations across the clinical timeline

Map Kamala's clinical timeline onto the spectrum of cellular adaptations: (a) early painless ulcer — which neural adaptation explains painlessness? (b) months of immobility — disuse atrophy of calf muscles; (c) chronic liver injury — hepatic steatosis as maladaptive accumulation; (d) endothelial stress from hyperglycaemia — metaplastic or adaptive change in vessel walls. For each, state whether the adaptation is physiological or pathological and whether it is reversible.
Research one clinical scenario where cellular aging mechanisms (telomere shortening, oxidative stress accumulation, p16/p21 upregulation) contribute directly to impaired wound healing in elderly diabetic patients.

Competencies: PA2.6, PA2.7, PA1.3

Group 5: The pathologist's role and clinico-pathological synthesis

Outline the role of the anatomic pathologist in Kamala's management: (a) intraoperative frozen section at the resection margin, (b) post-amputation specimen histology to confirm clear surgical margins and identify the type and zone of necrosis, (c) liver biopsy reporting — what clinical information must accompany the biopsy request for the pathologist to give a clinically useful report.
Write a mock histopathology report for the amputation specimen including: specimen description, microscopic findings for each zone (necrotic forefoot, border, viable tissue), final diagnosis with ICD code equivalents, and a clinical comment linking pathological findings to the patient's diabetic and vascular history.

Competencies: PA1.1, PA1.2, PA2.8

Learning Issues

Research these questions and bring your findings to the discussion.

[PA1.1] What is the specific role of the anatomic pathologist in the surgical management of a gangrenous limb, from intraoperative consultation to final histopathology reporting?
[PA1.2] Define the following terms used in this case and in pathology reporting: necrosis, apoptosis, gangrene, saponification, dystrophic calcification, adaptation, coagulative necrosis, ghost cells.
[PA1.3] How does the cell cycle relate to the capacity of different tissues (nerve, muscle, liver, bone marrow) to regenerate after injury — and why does this explain Kamala's non-healing wound?
[PA2.1] What are the main causes of cell injury in a diabetic foot ulcer, and how do they interact to push cells from adaptation to irreversible death?
[PA2.2] Describe the sequence of biochemical events from ischaemia-induced ATP depletion to irreversible membrane injury, identifying the specific event that represents the 'point of no return'.
[PA2.3] What substances accumulate in Kamala's liver cells, and what metabolic pathway produces each accumulation? How does lipid accumulation differ morphologically from hydropic swelling?
[PA2.4] Compare the morphological and mechanistic differences between coagulative and liquefactive necrosis, and explain why the dry zone of Kamala's foot shows one pattern while the wet zone shows another.
[PA2.5] What type of calcification is present in the border zone of Kamala's foot, and how does this differ from metastatic calcification in terms of serum calcium levels and mechanism?
[PA2.6] What cellular adaptations has Kamala's body made in response to chronic hyperglycaemia and immobility — specifically in her liver, calf muscles, and peripheral nerves — and which of these are reversible?
[PA2.7] What are the four main mechanisms of cellular ageing, and how might accelerated cellular ageing in Kamala's vascular endothelium and peripheral nerves contribute to her wound non-healing?
[PA2.8] Identify the histological features of gangrene on the gross specimen and microscopy — including the appearance of ghost cells, inflammatory demarcation line, and type of necrosis — and explain the difference between dry, wet, and gas gangrene.