A newborn male is evaluated in the hospital nursery two hours after birth. The patient was born at 39 weeks of gestation to a 30-year-old primigravid via vaginal delivery. The patient’s mother received routine prenatal care, and the pregnancy was uncomplicated. The patient’s anatomy ultrasound at 20 weeks of gestation was unremarkable. The patient’s mother denies any family history of genetic diseases. The patient’s Apgar scores were notable for poor muscle tone at both one and five minutes of life. The patient’s birth weight is 2.6 kg (5 lb 11 oz), which is at the 5th percentile. His height and head circumference are in the 15th and 3rd percentile, respectively. On physical exam, the patient has a wide nasal bridge, downslanting palpebral fissures, and widely spaced eyes. He has good respiratory effort with a high-pitched cry. This patient is most likely to have experienced a deletion on which of the following chromosomes?
Q12
A 3-year-old boy presents to a geneticist for generalized developmental delay. Upon presentation he is found to have a distinctive facial structure with prominent epicanthal folds and macroglossia. Further physical examination reveals a simian crease on his palms bilaterally. Based on these findings, the physician strongly suspects Down syndrome and obtains a karyotype. Surprisingly the karyotype shows 46 chromosomes with two normal appearing alleles of chromosome 21. Further examination with fluorescent probes reveals a third copy of chromosome 21 genes that have been incorporated into another chromosome. What is the name of this mechanism of Down syndrome inheritance?
Q13
A 3500-g (7 lb 11 oz) healthy female newborn is delivered at 38 weeks' gestation. Chorionic villus sampling (CVS) in the first trimester showed a trisomy of chromosome 21 but the pregnancy was otherwise uncomplicated. Physical examination of the newborn is normal. Chromosomal analysis at birth shows a 46, XX karyotype. Which of the following is the most likely explanation for the prenatal chromosomal abnormality?
Q14
A 10-year-old boy is brought to a pediatrician by his mother for evaluation of fever, malaise, and rash with severe itching all over his body for the past 5 days. His immunization history is unavailable. His vital signs include: pulse 110/min, temperature 37.8°C (100.0°F), and respiratory rate 26/min. On examination of the skin, diffuse peeling vesicular lesions involving the arms and chest are observed. The pediatrician diagnoses the boy with chickenpox and reassures the mother. A few days later the boy returns to the clinic for a follow-up with his mother. The skin lesions have healed and there are scars. The formation of these scars is best described by which of the following statements?
Q15
A 62-year-old woman with type 2 diabetes mellitus comes to the physician because of a 1-year history of progressively worsening paresthesias in her upper limbs. She has accidentally burned her fingers on hot dishes several times. She was involved in a motor vehicle collision 3 years ago. Neurologic examination shows absent temperature sensation with normal fine touch sensation over the upper extremities and chest. Without treatment, this patient is at increased risk of developing which of the following?
Q16
A pathologist examines a tissue specimen in which cells are grouped together in acini with visible ducts between them. He finds a patch of pale cells with a rich blood supply among the highly basophilic and granular cells. A representative micrograph is shown in the image. Which statement is correct about these cells?
Q17
An 80-year-old male is found dead at home and brought in for an autopsy. The patient's heart shows a diminished ventricular chamber volume and the interventricular septum appears sigmoid shaped. The left atrium appears enlarged as well. A few calcifications are seen on the undamaged aortic valves. Microscopic examination reveals increased connective tissue in the myocardium and brown perinuclear cytoplasmic granules in numerous myocardial cells as shown in the exhibit. Which of the following most likely explains this patient's cardiac findings?
Q18
An 80-year-old woman is brought to the physician by her 2 daughters for worsening memory loss. They report that their mother is increasingly forgetful about recent conversations and events. She is unable to remember her appointments and commitments she has made. 3 years ago, the patient was moved into an elder care facility because she was often getting lost on her way home and forgetting to take her medications. The patient reports that she is very socially active at her new home and has long conversations with the other residents about her adventures as an air hostess during her youth. Which of the following cerebral pathologies is most likely present in this patient?
Q19
A 17-year-old boy comes to the physician because of a nonpruritic rash on his chest for 1 week. He returned from a trip to Puerto Rico 10 days ago. He started using a new laundry detergent after returning. He has type 1 diabetes mellitus controlled with insulin. His mother has Hashimoto thyroiditis, and his sister has severe facial acne. Examination of the skin shows multiple, nontender, round, hypopigmented macules on the chest and trunk. There is fine scaling when the lesions are scraped with a spatula. Which of the following is the most likely underlying mechanism of this patient's symptoms?
Q20
A syndrome caused by chromosomal anomalies is being researched in the immunology laboratory. Several congenital conditions are observed among the participating patients, mostly involving the thymus and the heart. Common facial features of affected individuals are shown in the image below. Flow cytometry analysis of patient samples reveals a CD19+ and CD3- result. What kind of congenital anomaly is generally observed in these patients, specifically in the thymus?
General Pathology US Medical PG Practice Questions and MCQs
Question 11: A newborn male is evaluated in the hospital nursery two hours after birth. The patient was born at 39 weeks of gestation to a 30-year-old primigravid via vaginal delivery. The patient’s mother received routine prenatal care, and the pregnancy was uncomplicated. The patient’s anatomy ultrasound at 20 weeks of gestation was unremarkable. The patient’s mother denies any family history of genetic diseases. The patient’s Apgar scores were notable for poor muscle tone at both one and five minutes of life. The patient’s birth weight is 2.6 kg (5 lb 11 oz), which is at the 5th percentile. His height and head circumference are in the 15th and 3rd percentile, respectively. On physical exam, the patient has a wide nasal bridge, downslanting palpebral fissures, and widely spaced eyes. He has good respiratory effort with a high-pitched cry. This patient is most likely to have experienced a deletion on which of the following chromosomes?
A. 4p
B. 5q
C. 7q
D. 15q
E. 5p (Correct Answer)
Explanation: ***5p***
- The constellation of findings, including **low birth weight**, **microcephaly**, **hypotonia**, **widely spaced eyes**, **downslanting palpebral fissures**, **wide nasal bridge**, and a **high-pitched cry**, is highly characteristic of **Cri-du-chat syndrome**.
- **Cri-du-chat syndrome** is caused by a **deletion of the short arm of chromosome 5 (5p)**.
*4p*
- A deletion on **4p** is associated with **Wolf-Hirschhorn syndrome**, which presents with **microcephaly**, a distinct **"Greek helmet" facial appearance**, and often severe intellectual disability, which are not perfectly aligned with all features described.
- While there can be overlapping features like growth restriction and developmental delay, the specific craniofacial features and the characteristic cry of Cri-du-chat are not typical for Wolf-Hirschhorn syndrome.
*5q*
- A deletion on **5q** is associated with various conditions, including some forms of **myelodysplastic syndromes** (particularly 5q- syndrome), which are hematologic disorders and not typically presenting with the described birth defects.
- While deletions can occur on the long arm of chromosome 5, they do not cause Cri-du-chat syndrome; that is specifically a 5p deletion.
*7q*
- Deletions on **7q** are associated with conditions like **Williams syndrome** (a microdeletion on 7q11.23, characterized by "elfin" facies, supravalvular aortic stenosis, and unique personality traits) or **Silver-Russell syndrome** (associated with some 7q deletions, causing growth restriction and characteristic facial features).
- The described presentation does not match the typical features of conditions linked to 7q deletions.
*15q*
- Deletions on **15q** are linked to conditions such as **Prader-Willi syndrome** (paternal deletion of 15q11-q13, causing hypotonia, feeding difficulties in infancy followed by hyperphagia, and intellectual disability) and **Angelman syndrome** (maternal deletion or mutation on 15q11-q13, presenting with severe intellectual disability, ataxia, and inappropriate laughter).
- The clinical features presented do not align with the characteristic presentation of either Prader-Willi or Angelman syndrome.
Question 12: A 3-year-old boy presents to a geneticist for generalized developmental delay. Upon presentation he is found to have a distinctive facial structure with prominent epicanthal folds and macroglossia. Further physical examination reveals a simian crease on his palms bilaterally. Based on these findings, the physician strongly suspects Down syndrome and obtains a karyotype. Surprisingly the karyotype shows 46 chromosomes with two normal appearing alleles of chromosome 21. Further examination with fluorescent probes reveals a third copy of chromosome 21 genes that have been incorporated into another chromosome. What is the name of this mechanism of Down syndrome inheritance?
A. Robertsonian translocation (Correct Answer)
B. Nondisjunction
C. Anticipation
D. Imprinting
E. Mosaicism
Explanation: ***Robertsonian translocation***
- A Robertsonian translocation involves two **acrocentric chromosomes** (chromosomes 13, 14, 15, 21, 22) that fuse at their centromeres, with loss of their short arms, resulting in a single, large **derivative chromosome**.
- In this case, while the karyotype shows 46 chromosomes, the presence of a third copy of chromosome 21 genes incorporated into another chromosome, likely through the fusion of chromosome 21 with another acrocentric chromosome, leads to **trisomy 21** phenotype even though the total chromosome count is normal.
*Nondisjunction*
- **Nondisjunction** refers to the failure of homologous chromosomes or sister chromatids to separate during meiosis or mitosis, leading to an abnormal number of chromosomes (e.g., three separate copies of chromosome 21 in **trisomy 21**).
- This mechanism would typically result in a karyotype of **47,XX,+21** or **47,XY,+21** and would not explain the finding of 46 chromosomes with a third copy of chromosome 21 genes incorporated into another chromosome.
*Anticipation*
- **Anticipation** is a phenomenon in which the severity of a genetic disorder increases and/or the age of onset decreases in succeeding generations.
- This mechanism is characteristic of certain **trinucleotide repeat disorders** like Huntington's disease or myotonic dystrophy and does not explain the genetic findings associated with Down syndrome.
*Imprinting*
- **Genomic imprinting** is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin specific manner, meaning only the allele inherited from either the mother or the father is expressed.
- While important for some genetic disorders (e.g., Prader-Willi or Angelman syndromes), imprinting does not explain the presence of an extra copy of chromosome 21 genetic material leading to Down syndrome.
*Mosaicism*
- **Mosaicism** occurs when an individual has two or more genetically distinct cell lines originating from a single zygote, often due to a **nondisjunction event** during early postzygotic mitotic divisions.
- While mosaic Down syndrome can occur, it would typically present with some cells having **trisomy 21** (47,XX,+21) and other cells being normal (46,XX), not with 46 chromosomes and an extra set of chromosome 21 genes translocated onto another chromosome.
Question 13: A 3500-g (7 lb 11 oz) healthy female newborn is delivered at 38 weeks' gestation. Chorionic villus sampling (CVS) in the first trimester showed a trisomy of chromosome 21 but the pregnancy was otherwise uncomplicated. Physical examination of the newborn is normal. Chromosomal analysis at birth shows a 46, XX karyotype. Which of the following is the most likely explanation for the prenatal chromosomal abnormality?
A. Incomplete penetrance
B. Placental mosaicism (Correct Answer)
C. Phenotypic pleiotropy
D. Variable expressivity
E. Uniparental disomy
Explanation: ***Placental mosaicism***
- **Placental mosaicism** occurs when the chromosomal abnormality (e.g., trisomy 21) is present in the placenta but not in the fetus.
- This can lead to a false positive result on **chorionic villus sampling (CVS)** if the sampled tissue from the placenta contains the abnormal cells, while the fetus is truly euploid.
*Incomplete penetrance*
- **Incomplete penetrance** refers to a situation where individuals with a specific genotype do not always express the associated phenotype.
- This concept applies to single-gene disorders, not to a resolution of a **chromosomal abnormality** found during prenatal testing.
*Phenotypic pleiotropy*
- **Phenotypic pleiotropy** describes when a single gene mutation affects multiple, seemingly unrelated phenotypic traits.
- It does not explain a discrepancy between a prenatal chromosomal finding and a normal postnatal karyotype.
*Variable expressivity*
- **Variable expressivity** describes the range of signs and symptoms that can occur in different people with the same genetic condition.
- While it explains differing severity of a genetic disorder, it does not account for a complete resolution of a **chromosomal abnormality** from a trisomy to a normal karyotype.
*Uniparental disomy*
- **Uniparental disomy** occurs when an individual receives both copies of a chromosome from one parent and none from the other.
- While it can be associated with certain genetic disorders, it does not explain a situation where a prenatal trisomy completely resolves to a normal diploid karyotype.
Question 14: A 10-year-old boy is brought to a pediatrician by his mother for evaluation of fever, malaise, and rash with severe itching all over his body for the past 5 days. His immunization history is unavailable. His vital signs include: pulse 110/min, temperature 37.8°C (100.0°F), and respiratory rate 26/min. On examination of the skin, diffuse peeling vesicular lesions involving the arms and chest are observed. The pediatrician diagnoses the boy with chickenpox and reassures the mother. A few days later the boy returns to the clinic for a follow-up with his mother. The skin lesions have healed and there are scars. The formation of these scars is best described by which of the following statements?
A. The scars are permanent and remain for life in all cases.
B. The lesions now have progressed on to chronic inflammation.
C. The scars represent complete resolution of acute inflammation.
D. Neutrophils, plasma cells, and macrophages are the predominant cells in these lesions.
E. It is a part of the healing process of acute inflammation. (Correct Answer)
Explanation: ***It is a part of the healing process of acute inflammation.***
- The formation of scars after chickenpox reflects the body's attempt to repair tissue damage from the **vesicular lesions**, a direct consequence of the acute inflammatory response.
- Varicella-zoster virus (chickenpox) causes skin lesions that lead to localized tissue destruction, and subsequent **fibrosis** and scar formation are part of the normal healing with tissue repair.
*The scars are permanent and remain for life in all cases.*
- While many chickenpox scars are permanent, their **visibility and persistence can vary**, and some may fade significantly over time or with treatment.
- The depth and severity of the original lesion, as well as individual healing factors, influence the **permanence of the scar**.
*The lesions now have progressed on to chronic inflammation.*
- Scars indicate the **resolution of acute inflammation** and subsequent repair, not a progression to chronic inflammation.
- **Chronic inflammation** would involve ongoing active inflammation and tissue destruction, which is not characteristic of healed chickenpox scars.
*The scars represent complete resolution of acute inflammation.*
- While scars do represent the resolution of active inflammation, they signify **repair by fibrosis** rather than a "complete resolution" where the tissue returns to its original state.
- **Complete resolution** would imply restitution ad integrum (returning to normal tissue structure) without any residual scarring.
*Neutrophils, plasma cells, and macrophages are the predominant cells in these lesions.*
- These cells are characteristic of **active acute or chronic inflammatory processes**, not healed scars.
- Scars primarily consist of **collagen deposits** laid down by fibroblasts, with a much-reduced presence of inflammatory cells.
Question 15: A 62-year-old woman with type 2 diabetes mellitus comes to the physician because of a 1-year history of progressively worsening paresthesias in her upper limbs. She has accidentally burned her fingers on hot dishes several times. She was involved in a motor vehicle collision 3 years ago. Neurologic examination shows absent temperature sensation with normal fine touch sensation over the upper extremities and chest. Without treatment, this patient is at increased risk of developing which of the following?
A. Decreased Mini-Mental State Examination score
B. Drooping of the eyelid
C. Absent anal wink reflex
D. Absent knee-jerk reflex
E. Exaggerated biceps reflex (Correct Answer)
Explanation: ***Exaggerated biceps reflex***
- This patient presents with **syringomyelia**, characterized by a **cape-like distribution of dissociated sensory loss** (absent pain/temperature sensation with preserved fine touch over the upper extremities and chest), likely post-traumatic from the motor vehicle collision 3 years ago.
- As the syrinx expands, it can extend laterally to involve the **lateral corticospinal tracts**, leading to **upper motor neuron signs** including hyperreflexia in the upper limbs.
- While early syringomyelia may cause lower motor neuron signs (from anterior horn cell damage), progressive expansion of the cavity can result in exaggerated reflexes as corticospinal pathways are compromised.
*Decreased Mini-Mental State Examination score*
- This score assesses **cognitive function** and is not affected by syringomyelia, which primarily impacts **spinal cord tracts**.
- Syringomyelia does not cause dementia or cognitive decline.
*Drooping of the eyelid*
- **Ptosis** (drooping eyelid) can occur if the syrinx extends to **C8-T1** and damages sympathetic fibers in the **intermediolateral cell column**, causing Horner's syndrome.
- However, this is a less common complication compared to motor changes, and the clinical scenario doesn't suggest extension to this level yet.
*Absent anal wink reflex*
- The anal wink reflex tests the integrity of the **S2-S4 spinal segments** and **pudendal nerve**.
- Syringomyelia typically affects the **cervical or thoracic spine**, and the described presentation shows no evidence of lumbosacral involvement.
*Absent knee-jerk reflex*
- The knee-jerk reflex tests the **L2-L4 spinal segments**.
- The patient's sensory loss is confined to the upper extremities and chest, indicating a **cervical/upper thoracic syrinx** that would not directly affect lumbar reflexes.
Question 16: A pathologist examines a tissue specimen in which cells are grouped together in acini with visible ducts between them. He finds a patch of pale cells with a rich blood supply among the highly basophilic and granular cells. A representative micrograph is shown in the image. Which statement is correct about these cells?
A. These cells should be separated from the basophils by a dense capsule.
B. These cells are often found to be damaged in acute pancreatitis with a subsequent increase in serum amylase levels.
C. Some of these cells are capable of producing leptin, a hormone which regulates satiety.
D. Some of these cells undergo transformation and begin to secrete insulin to compensate for the loss of pancreatic beta cells.
E. There are several different types of cells within the patch that cannot be differentiated by light microscopy. (Correct Answer)
Explanation: ***There are several different types of cells within the patch that cannot be differentiated by light microscopy.***
- The description points to the **islets of Langerhans** within the pancreas, which are distinct from the exocrine pancreas (highly basophilic acini).
- The islets contain alpha, beta, delta, epsilon, and PP cells, each with different endocrine functions, which **appear homogeneous** under standard light microscopy.
*These cells should be separated from the basophils by a dense capsule.*
- The **islets of Langerhans** are well-vascularized endocrine clusters within the exocrine pancreas but they are **not encapsulated** from the surrounding acinar tissue.
- Instead, there is a **reticular fiber network** that separates the endocrine and exocrine components.
*These cells are often found to be damaged in acute pancreatitis with a subsequent increase in serum amylase levels.*
- In **acute pancreatitis**, it is primarily the **exocrine portion** of the pancreas (acinar cells) that is damaged, leading to the release of digestive enzymes like **amylase and lipase**.
- While severe pancreatitis can affect the islets, the initial and primary damage, along with the diagnostic enzyme elevation, is due to **exocrine cell injury**.
*Some of these cells are capable of producing leptin, a hormone which regulates satiety.*
- **Leptin** is primarily produced by **adipose tissue** and plays a crucial role in regulating energy balance and satiety.
- While the pancreas (specifically the islets) produces various hormones, **leptin is not one of them**.
*Some of these cells undergo transformation and begin to secrete insulin to compensate for the loss of pancreatic beta cells.*
- While the pancreas does exhibit some plasticity, the primary mechanism for regulating insulin in conditions like type 1 diabetes is not through other islet cells transforming into insulin-secreting cells.
- The compensatory mechanism for beta-cell loss is typically through **hyperplasia or hypertrophy of remaining beta-cells**, not the transformation of other islet cell types.
Question 17: An 80-year-old male is found dead at home and brought in for an autopsy. The patient's heart shows a diminished ventricular chamber volume and the interventricular septum appears sigmoid shaped. The left atrium appears enlarged as well. A few calcifications are seen on the undamaged aortic valves. Microscopic examination reveals increased connective tissue in the myocardium and brown perinuclear cytoplasmic granules in numerous myocardial cells as shown in the exhibit. Which of the following most likely explains this patient's cardiac findings?
A. Dilated cardiomyopathy
B. Uncontrolled hypertension
C. Chronic hemolytic anemia
D. Hypertrophic cardiomyopathy
E. Expected age related changes (Correct Answer)
Explanation: ***Expected age related changes***
- The combination of **diminished ventricular chamber volume**, **sigmoid septum**, **left atrial enlargement**, and **brown perinuclear cytoplasmic granules** (lipofuscin) is characteristic of **age-related cardiac atrophy**.
- Lipofuscin accumulation reflects **"brown atrophy"** - a hallmark of aging in postmitotic cells like cardiac myocytes, representing residual bodies from lysosomal digestion.
- **Increased connective tissue** (fibrosis) in the myocardium and calcifications on undamaged aortic valves are also common age-related findings, reflecting normal physiological changes in the elderly heart.
*Dilated cardiomyopathy*
- This condition is characterized by **ventricular dilation** and **systolic dysfunction**, which contradicts the diminished ventricular chamber volume described.
- While it can lead to left atrial enlargement, the overall cardiac morphology (especially reduced ventricular volume) does not fit.
*Uncontrolled hypertension*
- Chronic hypertension typically causes **left ventricular hypertrophy** with **concentric thickening** and often an **increased ejection fraction** initially.
- While it can lead to left atrial enlargement, it would not typically result in a diminished ventricular chamber volume or the characteristic sigmoid septum without other concurrent pathology.
*Chronic hemolytic anemia*
- Chronic severe anemia primarily leads to a **hyperdynamic circulation** and can cause **ventricular dilation** and hypertrophy over time due to increased cardiac output.
- It would not explain the observed diminished ventricular chamber volume, sigmoid septum, or lipofuscin deposition.
*Hypertrophic cardiomyopathy*
- Primarily defined by **marked left ventricular hypertrophy**, often asymmetric, which can involve the interventricular septum, leading to outflow tract obstruction.
- However, the description of a diminished ventricular chamber volume, along with lipofuscin granules, points more towards age-related changes rather than a primary hypertrophic cardiomyopathy, which often presents earlier in life and has a genetic predisposition.
Question 18: An 80-year-old woman is brought to the physician by her 2 daughters for worsening memory loss. They report that their mother is increasingly forgetful about recent conversations and events. She is unable to remember her appointments and commitments she has made. 3 years ago, the patient was moved into an elder care facility because she was often getting lost on her way home and forgetting to take her medications. The patient reports that she is very socially active at her new home and has long conversations with the other residents about her adventures as an air hostess during her youth. Which of the following cerebral pathologies is most likely present in this patient?
A. Lewy bodies
B. Lacunar infarcts
C. Intracytoplasmic vacuoles
D. Neurofibrillary tangles (Correct Answer)
E. Demyelination
Explanation: ***Neurofibrillary tangles***
- The patient's presentation with **progressive memory loss** affecting recent events, getting lost, and forgetting medications, while largely preserving long-term memory (recalling youth as an air hostess and engaging in conversations), is highly characteristic of **Alzheimer's disease**.
- **Neurofibrillary tangles**, composed of hyperphosphorylated tau protein, along with **amyloid plaques**, are the hallmark pathological findings in Alzheimer's disease.
*Lewy bodies*
- **Lewy bodies** are characteristic of **Lewy body dementia** or Parkinson's disease with dementia, which typically present with prominent **fluctuations in cognition**, recurrent **visual hallucinations**, and parkinsonism.
- While memory loss can occur, the dominant features in this case point away from Lewy body pathology.
*Lacunar infarcts*
- **Lacunar infarcts** are associated with **vascular dementia**, which often presents with a more **step-wise decline** in cognitive function, focal neurological deficits, and evidence of cerebrovascular disease on imaging.
- The patient's gradual and progressive memory loss is less typical of lacunar infarcts as the primary cause.
*Intracytoplasmic vacuoles*
- **Intracytoplasmic vacuoles** are characteristic of **Creutzfeldt-Jakob disease** (spongiform encephalopathy), which is a rapidly progressive and fatal neurodegenerative disorder with distinct neurological symptoms such as myoclonus and ataxia, not fitting this patient's profile.
- The disease course is typically much faster than the 3-year progression described.
*Demyelination*
- **Demyelination** is the hallmark of conditions like **multiple sclerosis**, which primarily affects younger individuals and typically presents with a range of neurological deficits, including motor, sensory, and visual disturbances, that often relapse and remit.
- It does not typically present as a primary, progressive memory disorder in an 80-year-old in this manner.
Question 19: A 17-year-old boy comes to the physician because of a nonpruritic rash on his chest for 1 week. He returned from a trip to Puerto Rico 10 days ago. He started using a new laundry detergent after returning. He has type 1 diabetes mellitus controlled with insulin. His mother has Hashimoto thyroiditis, and his sister has severe facial acne. Examination of the skin shows multiple, nontender, round, hypopigmented macules on the chest and trunk. There is fine scaling when the lesions are scraped with a spatula. Which of the following is the most likely underlying mechanism of this patient's symptoms?
A. Increased sebum production
B. Infection with Trichophyton rubrum
C. Increased growth of Malassezia globosa (Correct Answer)
D. Antigen uptake by Langerhans cells
E. Autoimmune destruction of melanocytes
Explanation: ***Increased growth of Malassezia globosa***
- The clinical presentation of **hypopigmented macules with fine scaling** on the chest and trunk, especially in a young male who recently traveled to a tropical climate (Puerto Rico), is highly characteristic of **tinea versicolor**.
- Tinea versicolor is caused by an overgrowth of **Malassezia species** (primarily *M. globosa*), a commensal yeast that thrives in warm, humid conditions and is often associated with oily skin, leading to dyspigmentation and scaling due to interference with melanin production.
*Increased sebum production*
- While increased sebum production can contribute to a favorable environment for fungal growth, it is the underlying mechanism for conditions like **acne vulgaris** and **seborrheic dermatitis**, which present differently (e.g., comedones, inflammatory papules, erythema, greasy scales).
- This patient's rash is specifically described as hypopigmented macules with fine scaling, not inflammatory papules or pustules typical of acne, nor the greasy scales of seborrheic dermatitis.
*Infection with Trichophyton rubrum*
- **Trichophyton rubrum** is a dermatophyte commonly responsible for **tinea corporis** (ringworm of the body), **tinea pedis** (athlete's foot), and **tinea cruris** (jock itch), which typically present as **erythematous, annular, itchy lesions with raised borders**.
- The rash described here (hypopigmented, nonpruritic macules) does not fit the typical presentation of dermatophyte infections caused by *Trichophyton rubrum*.
*Antigen uptake by Langerhans cells*
- **Antigen uptake by Langerhans cells** is a crucial step in the pathogenesis of **allergic contact dermatitis**, where the skin reacts to an external allergen after sensitization, mediated by a **Type IV hypersensitivity reaction**.
- While the patient used a new laundry detergent, the rash's appearance (**hypopigmented macules with fine scaling**) is incongruent with contact dermatitis, which usually presents as an **erythematous, pruritic, vesicular, or eczematous rash** in the contact area.
*Autoimmune destruction of melanocytes*
- **Autoimmune destruction of melanocytes** is the underlying mechanism for **vitiligo**, an autoimmune condition characterized by **well-demarcated, completely depigmented patches** of skin.
- The lesions in this patient are described as **hypopigmented** (reduced pigmentation), not completely depigmented, and show **fine scaling**, which is not a feature of vitiligo.
Question 20: A syndrome caused by chromosomal anomalies is being researched in the immunology laboratory. Several congenital conditions are observed among the participating patients, mostly involving the thymus and the heart. Common facial features of affected individuals are shown in the image below. Flow cytometry analysis of patient samples reveals a CD19+ and CD3- result. What kind of congenital anomaly is generally observed in these patients, specifically in the thymus?
A. Deformation
B. Malformation
C. Disruption
D. Aplasia (Correct Answer)
E. Agenesis
Explanation: ***Aplasia***
- The scenario describes **DiGeorge syndrome**, characterized by a **22q11.2 deletion**, leading to defective development of the 3rd and 4th pharyngeal pouches.
- This results in **thymic hypoplasia or aplasia**, causing **T-cell immunodeficiency** (CD3-), and **parathyroid aplasia**, leading to hypocalcemia.
- The CD19+ (B cells present) and CD3- (T cells absent) flow cytometry result specifically points to **thymic aplasia** as the cause for the lack of mature T-cells.
*Deformation*
- A deformation refers to an **abnormality in shape or position of a normally formed body part** due to extrinsic mechanical forces, such as uterine constraint.
- This is not the primary mechanism behind the thymic and cardiac anomalies described, which are due to inherent developmental defects.
*Malformation*
- A malformation is an **intrinsic abnormality of development** occurring during the embryonic period, due to genetic or environmental factors.
- While DiGeorge syndrome involves malformations (e.g., cardiac defects, characteristic facial features), the specific term for the complete or near-complete absence of an organ like the thymus is aplasia or hypoplasia, which is a more precise description in this context.
*Disruption*
- A disruption is a **morphological defect of an organ or body part from extrinsic breakdown of, or an interference with, an originally normal developmental process**.
- Examples include **amniotic bands** causing limb defects; this does not fit the description of a primary developmental defect of the pharyngeal pouches.
*Agenesis*
- Agenesis refers to the **complete absence of an organ** due to failure of development during embryonic growth.
- While agenesis is severe, **aplasia** (failure of development resulting in a rudimentary structure or complete absence) is often used interchangeably or to describe a more specific severe lack of development, especially in conditions like DiGeorge syndrome where there can be hypoplasia or complete absence. In clinical practice for DiGeorge, aplasia or hypoplasia is more commonly used for the thymus.