An 83-year-old woman with a history of atrial fibrillation, multiple ischemic strokes, and early dementia is found unresponsive in her apartment at her retirement community. She is believed to have not refilled any of her medications for a month, and it is determined that she passed away from a stroke nearly 2 weeks ago. The family is adamant that she receive an autopsy. Which of the following findings are most likely on brain histology?
Q2
A 64-year-old woman is brought to the emergency department 30 minutes after the onset of right-sided weakness and impaired speech. On admission, she is diagnosed with thrombotic stroke and treatment with alteplase is begun. Neurologic examination four weeks later shows residual right hemiparesis. A CT scan of the head shows hypoattenuation in the territory of the left middle cerebral artery. Which of the following processes best explains this finding?
Q3
A 38-year-old man is admitted to the hospital because of fever, yellowing of the skin, and nausea for 1 day. He recently returned from a backpacking trip to Brazil and Paraguay, during which he had a 3-day episode of high fever that resolved spontaneously. Physical examination shows jaundice, epigastric tenderness, and petechiae over his trunk. Five hours after admission, he develops dark brown emesis and anuria. Despite appropriate lifesaving measures, he dies. Postmortem liver biopsy shows eosinophilic degeneration of hepatocytes with condensed nuclear chromatin. This patient’s hepatocytes were most likely undergoing which of the following processes?
Q4
A 22-year-old man presents with an itchy rash. His physical exam reveals crusting vesicular clusters on an erythematous base with surrounding edema, located on his upper back. Which of the following is the most likely diagnosis?
Q5
A 75-year-old woman with a history of stroke 1 year ago was found unconscious on the floor of her home by her son. The patient was brought to the emergency department by ambulance but expired prior to arrival. An autopsy was performed and showed the cause of death to be a massive ischemic stroke. The coroner also examined sections taken from the area of her prior stroke. Which histologic finding would be prominent in the area of her stroke from one year prior?
Q6
A 62-year-old man goes to the emergency room (ER) for an intense lower abdominal pain associated with inability to urinate. Physical examination shows tenderness of the lower abdomen bilaterally. Rectal examination reveals an enlarged, smooth, and symmetrical prostate. The ER team fails to pass a Foley catheter through the urethra, and the urology team decides to place a suprapubic catheter to drain the urine and relieve the patient’s symptoms. An ultrasound shows dilation of the collecting system in both kidneys. Laboratory studies show an elevated serum creatinine of 1.6 mg/dL for an estimated glomerular filtration rate (eGFR) of 50 ml/min/1.73 m2. The patient visits the urology team for a follow-up visit 3 weeks after the acute event, in which he claims to have close to normal urination. However, his serum creatinine stays elevated at 1.5 mg/dL. What renal gross findings correlate with this patient’s condition?
Q7
A 13-year-old African-American boy is brought to the physician because of a 4-week history of left groin and buttock pain. The pain is worse with activity but also present at rest. He has had many episodes of abdominal, back, and chest pain that required hospitalization in the past. He is at the 20th percentile for height and 25th percentile for weight. His temperature is 36.7°C (98°F), blood pressure is 115/82 mm Hg, and pulse is 84/min. Examination shows tenderness over the lateral aspect of the left hip with no swelling, warmth, or erythema. There is pain with passive abduction and internal rotation of the left hip. Leukocyte count is 8,600/mm3. Which of the following is the most likely cause of this patient's symptoms?
Q8
A 55-year-old man is brought to the emergency room by his roommate due to an abdominal pain that started 2 hours ago. His pain is dull, aching, and radiates to the back. He admits to binge drinking alcohol for the past 2 days. Past medical history is significant for multiple admissions to the hospital for similar abdominal pain events, hypertension, and hyperlipidemia. He takes chlorthalidone and atorvastatin. He admits to heavy alcohol consumption over the past 10 years. He has smoked a pack of cigarettes a day for the last 20 years. In the emergency department, his temperature is 38.9℃ (102.0℉), pulse rate is 100/min, and respiratory rate is 28/min. On physical examination, he looks generally unwell and diaphoretic. Auscultation of his heart and lungs reveals an elevated heart rate with a regular rhythm. His lungs are clear to auscultation bilaterally. His abdomen is tympanitic with generalized tenderness. Evaluation of lab values reveals a leukocyte count of 28,000/mm3 with 89% of neutrophils. His amylase level is 255 U/L. A CT scan of the abdomen shows the diffuse enlargement of the pancreas. Which pathological process is most likely occurring in this patient’s peripancreatic tissue?
Q9
A 3-year-old boy is brought to the physician for a well-child examination. He has had multiple falls while walking and running for the past 4 months. He used to be able to climb stairs independently but now requires assistance. He started speaking in 2-word sentences at 2 years of age. He is at the 50th percentile for height and the 60th percentile for weight. Examination shows a waddling gait and enlargement of bilateral calves. Muscle strength is decreased in the bilateral lower extremities. Patellar and ankle reflexes are 1+ bilaterally. To rise from a sitting position, he uses his hands to support himself to an upright position. Diagnosis is confirmed by a muscle biopsy and immunohistochemistry. Which of the following is most likely responsible for the most severe clinical presentation of this disease?
Q10
A 72-year-old female is brought to the emergency department by ambulance because she was unable to walk. She says that she cut her leg while falling about a week ago. Since then, the wound has started draining fluid and become progressively more painful. She is found to have necrotizing fasciitis and is taken emergently to the operating room. Histological examination of cells along the fascial planes reveal cells undergoing necrosis. Which of the following represents the earliest sign that a cell has progressed to irreversible damage in this patient?
Cell injury US Medical PG Practice Questions and MCQs
Question 1: An 83-year-old woman with a history of atrial fibrillation, multiple ischemic strokes, and early dementia is found unresponsive in her apartment at her retirement community. She is believed to have not refilled any of her medications for a month, and it is determined that she passed away from a stroke nearly 2 weeks ago. The family is adamant that she receive an autopsy. Which of the following findings are most likely on brain histology?
A. Cellular debris and lymphocytes
B. Cystic cavitation (Correct Answer)
C. Fat saponification
D. Cellular debris and neutrophils
E. Increased binding of acidophilic dyes
Explanation: **Cystic cavitation**
- A **stroke** that occurred two weeks prior would most likely show **cystic cavitation** as the brain tissue attempts to repair itself after the damage.
- Over time, the necrotic tissue is removed, and a fluid-filled cavity forms, which is the final stage of **infarction resolution**.
*Cellular debris and lymphocytes*
- While **cellular debris** would be present, **lymphocytes** are typically later responders in inflammation, and at two weeks, the most prominent feature would be cavitation.
- **Microglia** and **macrophages** would be the primary cells involved in clearing debris, leading to cavitation.
*Fat saponification*
- **Fat saponification** is a type of **fat necrosis** seen in areas like the pancreas or breast, not typically in the brain after an ischemic stroke.
- This process involves the hydrolysis of triglycerides into fatty acids that combine with calcium, forming a chalky substance.
*Cellular debris and neutrophils*
- **Neutrophils** are characteristic of the very **early stages of acute inflammation**, typically within the first 24-48 hours after an ischemic stroke.
- By two weeks, most neutrophils would have resolved, and mononuclear cells and macrophages would predominate.
*Increased binding of acidophilic dyes*
- **Increased binding of acidophilic dyes** (like eosin) is seen in **early ischemic changes** (e.g., within hours to days), indicating **cell necrosis** like **red neurons**.
- At two weeks, the tissue has progressed beyond this immediate necrotic stage to active removal and cavitation.
Question 2: A 64-year-old woman is brought to the emergency department 30 minutes after the onset of right-sided weakness and impaired speech. On admission, she is diagnosed with thrombotic stroke and treatment with alteplase is begun. Neurologic examination four weeks later shows residual right hemiparesis. A CT scan of the head shows hypoattenuation in the territory of the left middle cerebral artery. Which of the following processes best explains this finding?
A. Liquefactive necrosis (Correct Answer)
B. Caseous necrosis
C. Gangrenous necrosis
D. Coagulative necrosis
E. Fat necrosis
Explanation: ***Liquefactive necrosis***
- This is the characteristic type of necrosis seen in the **central nervous system** following an ischemic insult like a stroke.
- The brain tissue is rapidly digested by hydrolytic enzymes, forming a **cyst-like cavity** filled with fluid (hence "hypoattenuation" on CT), reflecting the accumulation of necrotic cellular debris.
*Caseous necrosis*
- This is a form of cell death typically associated with **tuberculous infections** and some fungal infections.
- It results in the formation of a cheesy, friable material consisting of fragmented cells and granular debris, which is not characteristic of stroke.
*Gangrenous necrosis*
- This type of necrosis is typically seen in the **extremities** and is often associated with a loss of blood supply and subsequent bacterial infection.
- It involves tissue death due to ischemia, often accompanied by signs of putrefaction, making it distinct from a brain infarct.
*Coagulative necrosis*
- This is the most common type of necrosis and occurs in solid organs (e.g., heart, kidney) due to **ischemia**, preserving the architectural outlines of the dead cells for a period.
- Unlike the brain, where rapid liquefaction occurs, coagulative necrosis is not the primary form of cell death observed in the central nervous system after an ischemic stroke.
*Fat necrosis*
- This occurs in **adipose tissue**, usually due to trauma or enzymatic digestion (e.g., in pancreatitis).
- It involves the breakdown of fats into fatty acids, which then combine with calcium to form chalky white areas, which is not relevant to a cerebral infarct.
Question 3: A 38-year-old man is admitted to the hospital because of fever, yellowing of the skin, and nausea for 1 day. He recently returned from a backpacking trip to Brazil and Paraguay, during which he had a 3-day episode of high fever that resolved spontaneously. Physical examination shows jaundice, epigastric tenderness, and petechiae over his trunk. Five hours after admission, he develops dark brown emesis and anuria. Despite appropriate lifesaving measures, he dies. Postmortem liver biopsy shows eosinophilic degeneration of hepatocytes with condensed nuclear chromatin. This patient’s hepatocytes were most likely undergoing which of the following processes?
A. Regeneration
B. Steatosis
C. Necrosis
D. Apoptosis (Correct Answer)
E. Proliferation
Explanation: ***Apoptosis***
- The patient's symptoms (fever, jaundice, epigastric tenderness, petechiae, dark emesis, anuria) and history of travel to endemic areas are highly suggestive of **Yellow Fever**.
- **Eosinophilic degeneration of hepatocytes with condensed nuclear chromatin**, described as **Councilman bodies** or **apoptotic bodies**, is a characteristic histological finding in Yellow Fever and indicates programmed cell death.
*Regeneration*
- This process involves the replacement of damaged tissue with new, healthy tissue, which would contradict the patient's rapidly deteriorating condition and death.
- While regeneration can occur in the liver, the described histological findings of **eosinophilic degeneration** and **condensed nuclear chromatin** are indicative of cell death, not repair.
*Steatosis*
- **Steatosis** refers to the accumulation of fat droplets within hepatocytes, which is usually seen in conditions like alcoholic liver disease or non-alcoholic fatty liver disease.
- This is not consistent with the eosinophilic degeneration and condensed chromatin described, which point to a different type of cellular injury.
*Necrosis*
- **Necrosis** is a form of unregulated cell death often associated with inflammation and cellular swelling; the description of **eosinophilic degeneration** and **condensed nuclear chromatin** points specifically to apoptotic cell death rather than necrotic changes which would typically include cell swelling and rupture.
- While Yellow Fever does cause significant liver damage leading to cell death, the specific histological features (e.g., Councilman bodies) are characteristic of **apoptosis**, not typically seen in necrosis.
*Proliferation*
- **Proliferation** refers to an increase in the number of cells, typically in response to a stimulus or as part of a disease process like cancer.
- The patient's rapid decline and the histological findings of dying cells (eosinophilic degeneration, condensed chromatin) are antithetical to cellular proliferation.
Question 4: A 22-year-old man presents with an itchy rash. His physical exam reveals crusting vesicular clusters on an erythematous base with surrounding edema, located on his upper back. Which of the following is the most likely diagnosis?
A. Herpes simplex virus infection
B. Impetigo
C. Atopic eczema
D. Herpes zoster (Correct Answer)
E. Contact dermatitis
Explanation: ***Herpes zoster***
- The description of **crusting vesicular clusters on an erythematous base with surrounding edema** is highly characteristic of **herpes zoster** (shingles).
- While not explicitly mentioned, herpes zoster typically follows a **dermatomal distribution**, which would explain a localized rash on the upper back.
*Herpes simplex virus infection*
- HSV lesions are also vesicular but usually present as **grouped vesicles on an erythematous base**, often around the mouth (cold sores) or genitals.
- Unlike zoster, HSV **causes** recurrent infections at the same site, and widespread lesions are rare in immunocompetent individuals.
*Impetigo*
- Impetigo is a superficial bacterial infection characterized by **honey-colored crusts** that develop from ruptured vesicles or bullae.
- While it can be vesicular, the primary lesions are typically **pustules** or vesicles that rapidly become crusted, and the characteristic honey-colored crust is a key differentiating feature.
*Atopic eczema*
- Atopic eczema presents with **erythematous, intensely pruritic patches and plaques**, often with lichenification in chronic cases.
- While vesicles can occur during acute flares, the predominant features are usually dry, scaly skin and intense itching, without the prominent clustering of vesicles seen in the patient.
*Contact dermatitis*
- Contact dermatitis manifests as an **itchy, erythematous rash** that appears at the site of contact with an allergen or irritant.
- It can include vesicles, but the rash typically has clear borders reflecting the area of contact and often does not show the highly grouped, clustered pattern characteristic of shingles.
Question 5: A 75-year-old woman with a history of stroke 1 year ago was found unconscious on the floor of her home by her son. The patient was brought to the emergency department by ambulance but expired prior to arrival. An autopsy was performed and showed the cause of death to be a massive ischemic stroke. The coroner also examined sections taken from the area of her prior stroke. Which histologic finding would be prominent in the area of her stroke from one year prior?
A. Necrosis and neutrophils
B. Red neurons
C. Macrophages
D. Cyst formed by astrocyte processes (Correct Answer)
E. Reactive gliosis and vascular proliferation
Explanation: ***Cyst formed by astrocyte processes***
- After a significant ischemic stroke, the brain tissue undergoes liquefactive necrosis. Over time (months to a year), the necrotic tissue is removed by macrophages, leaving behind a fluid-filled cavity or **cyst**.
- This cyst is typically surrounded by a wall of **reactive astrocytes** (gliosis) which form a glial scar to contain the damage.
*Necrosis and neutrophils*
- **Necrosis** is characteristic of acute ischemic injury, but neutrophils are prominent only in the very early stages (hours to days) of inflammation.
- One year after a stroke, neutrophils would no longer be present; the area would have progressed beyond acute inflammation.
*Red neurons*
- **Red neurons** are an early histological sign of irreversible neuronal damage due to ischemia, appearing within **12-24 hours** after the insult.
- They represent acute cell death but would have long been cleared by a year post-stroke.
*Macrophages*
- **Macrophages** (microglia) are actively involved in clearing necrotic debris from the stroke site, primarily within **days to weeks** after the event.
- While still present, they are less prominent than the established cyst and glial scar at **one year**.
*Reactive gliosis and vascular proliferation*
- **Reactive gliosis** (astrocytic activation) is indeed a component of the long-term response to injury, contributing to the formation of the cyst wall.
- However, **vascular proliferation** is more characteristic of subacute infarcts (weeks) and less dominant than the mature cystic lesion at one year.
Question 6: A 62-year-old man goes to the emergency room (ER) for an intense lower abdominal pain associated with inability to urinate. Physical examination shows tenderness of the lower abdomen bilaterally. Rectal examination reveals an enlarged, smooth, and symmetrical prostate. The ER team fails to pass a Foley catheter through the urethra, and the urology team decides to place a suprapubic catheter to drain the urine and relieve the patient’s symptoms. An ultrasound shows dilation of the collecting system in both kidneys. Laboratory studies show an elevated serum creatinine of 1.6 mg/dL for an estimated glomerular filtration rate (eGFR) of 50 ml/min/1.73 m2. The patient visits the urology team for a follow-up visit 3 weeks after the acute event, in which he claims to have close to normal urination. However, his serum creatinine stays elevated at 1.5 mg/dL. What renal gross findings correlate with this patient’s condition?
A. Thin cortical rim (Correct Answer)
B. Granular surface
C. Ureteropelvic junction narrowing
D. Enlarged kidneys with bosselated surface
E. Pale cortical deposits
Explanation: ***Thin cortical rim***
- This patient has **acute obstructive nephropathy** from benign prostatic hyperplasia (BPH) causing bilateral hydronephrosis.
- The ultrasound showing **dilation of the collecting system** in both kidneys and persistent elevated creatinine despite relief of obstruction indicates **hydronephrosis with cortical damage**.
- The classic gross finding in hydronephrosis is **thinning of the renal cortex** due to compression from dilated calyces and renal pelvis, creating a **thin cortical rim** appearance.
- Even though obstruction was relieved after 3 weeks, the persistent creatinine elevation suggests **permanent nephron loss** from cortical atrophy.
*Granular surface*
- A **granular surface** is the gross finding of **chronic glomerulonephritis** or end-stage chronic kidney disease from various causes, resulting from cortical scarring and fibrosis.
- This develops over **years**, not weeks, and represents chronic irreversible damage from conditions like hypertensive nephrosclerosis, diabetic nephropathy, or chronic glomerulonephritis.
- This patient's 3-week obstruction is too acute to produce chronic granular scarring.
*Pale cortical deposits*
- **Pale cortical deposits** might be seen in conditions like **amyloidosis** or some forms of acute tubular necrosis with extensive tubular casts.
- This is not characteristic of obstructive nephropathy or hydronephrosis.
*Ureteropelvic junction narrowing*
- **UPJ narrowing** is an anatomical finding (a cause of obstruction), not a gross finding of the renal parenchyma itself.
- While UPJ obstruction can cause hydronephrosis, this patient's obstruction is at the bladder outlet (prostatic), not at the UPJ.
*Enlarged kidneys with bosselated surface*
- **Bosselated surface with enlarged kidneys** is pathognomonic for **autosomal dominant polycystic kidney disease (ADPKD)**, where multiple cysts distort the renal architecture.
- This patient's presentation is consistent with obstructive nephropathy from BPH, not inherited cystic disease.
Question 7: A 13-year-old African-American boy is brought to the physician because of a 4-week history of left groin and buttock pain. The pain is worse with activity but also present at rest. He has had many episodes of abdominal, back, and chest pain that required hospitalization in the past. He is at the 20th percentile for height and 25th percentile for weight. His temperature is 36.7°C (98°F), blood pressure is 115/82 mm Hg, and pulse is 84/min. Examination shows tenderness over the lateral aspect of the left hip with no swelling, warmth, or erythema. There is pain with passive abduction and internal rotation of the left hip. Leukocyte count is 8,600/mm3. Which of the following is the most likely cause of this patient's symptoms?
A. Avascular necrosis (Correct Answer)
B. Impaired skeletal growth
C. Transient synovitis
D. Septic arthritis
E. Proximal femoral osteosarcoma
Explanation: ***Avascular necrosis***
- The patient's history of recurrent pain crises (abdominal, back, chest pain) and **African-American ethnicity** strongly suggest **sickle cell disease**, where vascular occlusion can lead to **avascular necrosis (AVN)** of bone.
- The presenting symptoms of chronic groin and buttock pain, particularly with activity and at rest, and pain on hip movement (abduction, internal rotation) are classic for **femoral head AVN**.
*Impaired skeletal growth*
- While patients with chronic diseases like sickle cell can have impaired growth, this option describes a **general growth problem**, not a specific acute cause of severe hip pain.
- Impaired skeletal growth itself does not typically cause **localized, acute groin and buttock pain** that is worsened by movement.
*Transient synovitis*
- This condition is typically **acute and self-limiting**, lasting usually a few days to a week, not 4 weeks, and commonly follows a viral illness.
- It primarily affects younger children (ages 3-8) and is less common in adolescents with a history suggestive of sickle cell disease.
*Septic arthritis*
- Septic arthritis presents with **acute onset of severe pain**, fever, and local signs of inflammation like warmth, swelling, and erythema, which are absent in this case.
- The patient's **leukocyte count is normal** (8,600/mm3), which makes septic arthritis less likely.
*Proximal femoral osteosarcoma*
- Osteosarcoma usually presents with **progressively worsening bone pain** and often a palpable mass or swelling, which is not described here.
- While rare, it's less likely given the patient's strong history suggestive of an underlying condition that predisposes to AVN.
Question 8: A 55-year-old man is brought to the emergency room by his roommate due to an abdominal pain that started 2 hours ago. His pain is dull, aching, and radiates to the back. He admits to binge drinking alcohol for the past 2 days. Past medical history is significant for multiple admissions to the hospital for similar abdominal pain events, hypertension, and hyperlipidemia. He takes chlorthalidone and atorvastatin. He admits to heavy alcohol consumption over the past 10 years. He has smoked a pack of cigarettes a day for the last 20 years. In the emergency department, his temperature is 38.9℃ (102.0℉), pulse rate is 100/min, and respiratory rate is 28/min. On physical examination, he looks generally unwell and diaphoretic. Auscultation of his heart and lungs reveals an elevated heart rate with a regular rhythm. His lungs are clear to auscultation bilaterally. His abdomen is tympanitic with generalized tenderness. Evaluation of lab values reveals a leukocyte count of 28,000/mm3 with 89% of neutrophils. His amylase level is 255 U/L. A CT scan of the abdomen shows the diffuse enlargement of the pancreas. Which pathological process is most likely occurring in this patient’s peripancreatic tissue?
A. Fat necrosis (Correct Answer)
B. Caseous necrosis
C. Fibrinoid necrosis
D. Coagulative necrosis
E. Liquefactive necrosis
Explanation: ***Fat necrosis***
- This patient presents with **acute pancreatitis**, characterized by severe epigastric pain radiating to the back, elevated amylase, and diffuse pancreatic enlargement on CT, all exacerbated by **binge drinking**.
- In acute pancreatitis, activated pancreatic enzymes, particularly **lipases**, leak into the peripancreatic fat, causing enzymatic breakdown of fat into fatty acids, which then combine with calcium to form **calcium soaps** (saponification), clinically recognizable as fat necrosis.
*Caseous necrosis*
- This type of necrosis is typically associated with **tuberculosis** and fungal infections, forming a cheesy, crumbly appearance.
- It involves a granulomatous inflammatory response and does not align with the enzyme-driven fat breakdown seen in pancreatitis.
*Fibrinoid necrosis*
- This is a vascular injury characterized by the deposition of **fibrin-like material** in arterial walls, often seen in immune-mediated vasculitis or severe hypertension.
- It is not a primary pathological process in the peripancreatic tissue during acute pancreatitis.
*Coagulative necrosis*
- This form of necrosis is characteristic of **ischemic injury** in most solid organs (e.g., heart, kidney) where the cellular architecture is preserved for some time.
- While pancreatic necrosis can occur, the specific breakdown of peripancreatic fat by lipases leads to fat necrosis, not coagulative necrosis of the fat itself.
*Liquefactive necrosis*
- This type of necrosis occurs in tissues rich in hydrolytic enzymes and low in structural proteins, such as the **brain after ischemia** or in **abscesses**.
- While pancreatic tissue undergoing severe necrosis can exhibit liquefaction, the specific process affecting the surrounding fat in pancreatitis is fat necrosis due to lipase activity.
Question 9: A 3-year-old boy is brought to the physician for a well-child examination. He has had multiple falls while walking and running for the past 4 months. He used to be able to climb stairs independently but now requires assistance. He started speaking in 2-word sentences at 2 years of age. He is at the 50th percentile for height and the 60th percentile for weight. Examination shows a waddling gait and enlargement of bilateral calves. Muscle strength is decreased in the bilateral lower extremities. Patellar and ankle reflexes are 1+ bilaterally. To rise from a sitting position, he uses his hands to support himself to an upright position. Diagnosis is confirmed by a muscle biopsy and immunohistochemistry. Which of the following is most likely responsible for the most severe clinical presentation of this disease?
A. Frameshift mutation (Correct Answer)
B. Missense mutation
C. Silent mutation
D. Splice site mutation
E. Same sense mutation
Explanation: ***Frameshift mutation***
- The patient's presentation with **waddling gait**, **Gowers' sign**, **calf pseudohypertrophy**, and progressive muscle weakness is characteristic of **Duchenne Muscular Dystrophy (DMD)**.
- **Frameshift mutations** in the **dystrophin gene** lead to a premature stop codon, resulting in a severely truncated and non-functional dystrophin protein, causing the most severe form of the disease.
*Missense mutation*
- A **missense mutation** results in a single amino acid change, which may lead to a partially functional protein.
- This type of mutation typically causes **Becker Muscular Dystrophy (BMD)**, which is a milder form compared to DMD, with later onset and slower progression.
*Silent mutation*
- A **silent mutation** codes for the same amino acid, having no effect on the protein sequence or function.
- Therefore, it would not lead to any clinical disease, let alone the severe presentation described.
*Splice site mutation*
- A **splice site mutation** can lead to altered mRNA splicing, potentially resulting in exon skipping or intron retention.
- If the mutation disrupts the reading frame (out-of-frame), it causes DMD with complete loss of dystrophin; if the reading frame is maintained (in-frame), it causes milder BMD with partially functional dystrophin.
- However, a frameshift mutation specifically guarantees reading frame disruption and the most severe phenotype.
*Same sense mutation*
- This term is synonymous with a **silent mutation** or a **synonymous mutation**, meaning it results in the same, unchanged amino acid sequence due to the redundancy of the genetic code.
- As such, it would not alter protein function and would not cause a clinical disease.
Question 10: A 72-year-old female is brought to the emergency department by ambulance because she was unable to walk. She says that she cut her leg while falling about a week ago. Since then, the wound has started draining fluid and become progressively more painful. She is found to have necrotizing fasciitis and is taken emergently to the operating room. Histological examination of cells along the fascial planes reveal cells undergoing necrosis. Which of the following represents the earliest sign that a cell has progressed to irreversible damage in this patient?
A. Fragmentation of the nucleus
B. Membrane blebbing from organelles
C. Chromatin dissolution and disappearance
D. Ribosomal detachment from the endoplasmic reticulum
E. Condensation of DNA into a basophilic mass (Correct Answer)
Explanation: ***Condensation of DNA into a basophilic mass***
- **Karyopyknosis**, or the **condensation of nuclear chromatin into a dense, shrunken mass**, is an early microscopic sign of irreversible cell injury leading to necrosis. It indicates the cell has committed to a death pathway.
- This nuclear change is characterized by the nucleus appearing as a **small, dense, and deeply basophilic structure** due to chromatin clumping.
*Fragmentation of the nucleus*
- **Karyorrhexis**, the fragmentation of the pyknotic nucleus, occurs *after* karyopyknosis, indicating a later stage of irreversible injury.
- This process involves the breakdown of the condensed nuclear fragments, leading to their subsequent disappearance.
*Membrane blebbing from organelles*
- **Membrane blebbing** can occur in both reversible and irreversible injury, but its presence on *organelles* specifically doesn't necessarily represent the *earliest* sign of irreversible damage compared to nuclear changes.
- While significant blebbing points towards severe damage, **nuclear changes** are often considered more definitive early markers of irreversible commitment.
*Chromatin dissolution and disappearance*
- **Karyolysis**, the dissolution and fading of the nucleus due to enzymatic degradation, represents a *later* stage of irreversible injury, occurring after karyopyknosis and karyorrhexis.
- In this stage, the nucleus eventually completely disappears, leaving only an anucleated ghost cell.
*Ribosomal detachment from the endoplasmic reticulum*
- **Ribosomal detachment** from the endoplasmic reticulum is an early sign of **reversible cell injury**, leading to decreased protein synthesis.
- It indicates initial cellular stress but not necessarily a commitment to irreversible damage or necrosis.
