A 36-year-old man is brought to the emergency department by his wife 20 minutes after having a seizure. Over the past 3 days, he has had a fever and worsening headaches. This morning, his wife noticed that he was irritable and demonstrated strange behavior; he put the back of his fork, the salt shaker, and the lid of the coffee can into his mouth. He has no history of serious illness and takes no medications. His temperature is 39°C (102.2°F), pulse is 88/min, and blood pressure is 118/76 mm Hg. Neurologic examination shows diffuse hyperreflexia and an extensor response to the plantar reflex on the right. A T2-weighted MRI of the brain shows edema and areas of hemorrhage in the left temporal lobe. Which of the following is most likely the primary mechanism of the development of edema in this patient?
Q32
A 3-year-old male is brought by his mother to the pediatrician because she is concerned about a lump in his neck. She reports that the child was recently ill with a cough, nasal congestion, and rhinorrhea. She also noticed that a small red lump developed on the patient’s neck while he was sick. Although his cough and congestion subsided after a few days, the neck lump has persisted. The child has no notable past medical history. He was born at 39 weeks gestation and is in the 55th percentiles for both height and weight. His temperature is 98.6°F (37°C), blood pressure is 105/65 mmHg, pulse is 90/min, and respirations are 18/min. Physical examination reveals a small, soft, rounded mass at the midline of the neck inferior to the hyoid bone. The mass is warm and tender to palpation. It moves superiorly when the patient drinks water. Histologic examination of this lesion would most likely reveal which of the following?
Q33
A 50-year-old female presents to her physician with vesicles and tense blisters across her chest, arms, and the back of her shoulders. Physical examination reveals that blistering is not present in her oral mucosa, and the epidermis does not separate upon light stroking of the skin. The patient most likely suffers from a hypersensitivity reaction located:
Q34
A 6-year-old boy is brought to the emergency department due to a severe infection. Laboratory work shows leukocytosis of 60 × 109/L with marked left shift, but no blast cells. The patient is febrile and dehydrated. The physician believes that this is a severe reaction to the infection and orders a leukocyte alkaline phosphatase (LAP) stain on a peripheral smear. The LAP score is elevated. Which of the following statements best describes an additional characteristic of the condition this child is suffering from?
Q35
A 40-year-old man presents with a swollen left big toe that started this morning. The patient states that he attended a party last night and drank 4 glasses of whiskey. He denies any trauma to the foot. The patient has a history of similar episodes in the past that were related to alcohol use. His symptoms were previously relieved with ibuprofen. However, the pain persisted despite treatment with the medication. Physical examination reveals a tender and erythematous, swollen left 1st metatarsophalangeal joint. Which of the following events most likely contributed to his condition?
Q36
A 42-year-old woman with well-controlled HIV on antiretroviral therapy comes to the physician because of a 2-week history of a painless lesion on her right calf. Many years ago, she had a maculopapular rash over her trunk, palms, and soles that resolved spontaneously. Physical examination shows a 4-cm firm, non-tender, indurated ulcer with a moist, dark base and rolled edges. There is a similar lesion at the anus. Results of rapid plasma reagin testing are positive. Which of the following findings is most likely on microscopic examination of these lesions?
Q37
A 10-year-old boy presents with sudden shortness of breath. The patient’s mother says he was playing in the school garden 2 hours ago and suddenly started to complain of abdominal pain and vomited a few times. An hour later, he slowly developed a rash that involved his chest, arms, and legs, and his breathing became faster, with audible wheezing. He has no significant past medical history. His temperature is 37.0°C (98.6°F), blood pressure is 100/60 mm Hg, pulse is 130/min, and respirations are 25/min. On physical examination, there is a rash on his right arm (shown in the image, below). Which of the following cells will mainly be found in this patient if a histological sample is taken from the site of the skin lesion 4 hours from now?
Q38
A 27-year-old man comes to the physician because of multiple, dry, scaly lesions on his elbows. The lesions appeared 4 months ago and have progressively increased in size. They are itchy and bleed when he scratches them. There is no associated pain or discharge. He was diagnosed with HIV infection 6 years ago. He has smoked a pack of cigarettes daily for the past 10 years. Current medications include raltegravir, lamivudine, abacavir, and cotrimoxazole. An image of the lesions is shown. His CD4+ T-lymphocyte count is 470/mm3 (normal ≥ 500). Which of the following is the most likely cause of this patient's skin findings?
Q39
A 37-year-old woman presents to the occupational health clinic for a new employee health screening. She has limited medical records prior to her immigration to the United States several years ago. She denies any current illness or significant medical history. Purified protein derivative (PPD) is injected on the inside of her left forearm for tuberculosis (TB) screening. Approximately 36 hours later, the patient comes back to the occupational health clinic and has an indurated lesion with bordering erythema measuring 15 mm in diameter at the site of PPD injection. Of the following options, which is the mechanism of her reaction?
Q40
A 22-year-old woman comes to the physician because of pain and swelling of her left foot. Three days ago, she cut her foot on an exposed rock at the beach. Her temperature is 37.7°C (100°F). Examination of the left foot shows edema around a fluctuant erythematous lesion on the lateral foot. Which of the following is most likely the primary mechanism for the development of edema in this patient?
Inflammation US Medical PG Practice Questions and MCQs
Question 31: A 36-year-old man is brought to the emergency department by his wife 20 minutes after having a seizure. Over the past 3 days, he has had a fever and worsening headaches. This morning, his wife noticed that he was irritable and demonstrated strange behavior; he put the back of his fork, the salt shaker, and the lid of the coffee can into his mouth. He has no history of serious illness and takes no medications. His temperature is 39°C (102.2°F), pulse is 88/min, and blood pressure is 118/76 mm Hg. Neurologic examination shows diffuse hyperreflexia and an extensor response to the plantar reflex on the right. A T2-weighted MRI of the brain shows edema and areas of hemorrhage in the left temporal lobe. Which of the following is most likely the primary mechanism of the development of edema in this patient?
A. Increased hydrostatic pressure
B. Breakdown of endothelial tight junctions (Correct Answer)
C. Release of vascular endothelial growth factor
D. Cellular retention of sodium
E. Degranulation of eosinophils
Explanation: ***Breakdown of endothelial tight junctions***
- The patient's symptoms (fever, headache, seizure, behavioral changes, focal neurological deficits) and MRI findings (edema, hemorrhage in the left temporal lobe) are highly suggestive of **herpes simplex encephalitis (HSE)**.
- In HSE, the **inflammation** caused by viral infection leads to the breakdown of the **blood-brain barrier (BBB)**, primarily through the disruption of **endothelial tight junctions**, resulting in vasogenic edema and hemorrhage.
*Increased hydrostatic pressure*
- Increased hydrostatic pressure typically causes edema in conditions like **heart failure** or **venous obstruction**, where there is a systemic or localized increase in intravascular pressure.
- While hydrostatic pressure contributes to fluid movement, it is not the primary mechanism of BBB breakdown and edema development in **viral encephalitis**, where inflammation-induced endothelial damage is key.
*Release of vascular endothelial growth factor*
- **VEGF** is a potent pro-angiogenic and permeability-enhancing factor often associated with **tumor-related edema** or certain inflammatory conditions where new vessel formation is prominent.
- While it can increase vascular permeability, the primary and most direct mechanism for the widespread edema and hemorrhage described in acute viral encephalitis involves **direct endothelial damage and tight junction disruption**.
*Cellular retention of sodium*
- **Cellular retention of sodium** is characteristic of **cytotoxic edema**, which occurs when cellular energy failure (e.g., in ischemia) impairs the Na+/K+-ATPase pump, leading to intracellular water accumulation.
- Although cytotoxic edema can coexist, the MRI findings of **hemorrhage** and significant interstitial edema point more strongly to **vasogenic edema** due to BBB disruption.
*Degranulation of eosinophils*
- **Eosinophil degranulation** is primarily associated with **allergic reactions**, **parasitic infections**, and certain **autoimmune vasculitides**.
- While inflammation is present, eosinophils do not play a significant primary role in the mechanism of edema formation in acute viral encephalitis like HSE.
Question 32: A 3-year-old male is brought by his mother to the pediatrician because she is concerned about a lump in his neck. She reports that the child was recently ill with a cough, nasal congestion, and rhinorrhea. She also noticed that a small red lump developed on the patient’s neck while he was sick. Although his cough and congestion subsided after a few days, the neck lump has persisted. The child has no notable past medical history. He was born at 39 weeks gestation and is in the 55th percentiles for both height and weight. His temperature is 98.6°F (37°C), blood pressure is 105/65 mmHg, pulse is 90/min, and respirations are 18/min. Physical examination reveals a small, soft, rounded mass at the midline of the neck inferior to the hyoid bone. The mass is warm and tender to palpation. It moves superiorly when the patient drinks water. Histologic examination of this lesion would most likely reveal which of the following?
A. Stratified squamous epithelium associated with hair follicles and sebaceous glands
B. Randomly oriented papillae with fibrovascular cores and empty-appearing nuclei
C. Diffuse hyperplasia and hypertrophy of follicular cells
D. Follicular cells surrounding colloid and admixed with a neutrophilic infiltrate (Correct Answer)
E. Cyst-like structure lined by stratified squamous epithelium and containing mucoid material
Explanation: ***Follicular cells surrounding colloid and admixed with a neutrophilic infiltrate***
- The presentation of a **midline neck mass inferior to the hyoid bone** that moves with swallowing (drinking water), developing after an upper respiratory infection and being **warm and tender**, is highly suggestive of an infected **thyroglossal duct cyst**.
- A thyroglossal duct cyst is derived from remnants of the **thyroglossal duct**, which is normally lined by **thyroid follicular epithelium**. In the presence of infection, such as a prior URI, these cysts can become inflamed, leading to the accumulation of **colloid**, **inflammatory cells (neutrophils)**, and debris within the cyst lumen.
*Stratified squamous epithelium associated with hair follicles and sebaceous glands*
- This describes the histological features of an **epidermoid cyst** or **pilar cyst**, which are typically found in the skin and contain keratinous material.
- These cysts are usually **not midline** and do not typically move with swallowing, distinguishing them from the described lesion.
*Randomly oriented papillae with fibrovascular cores and empty-appearing nuclei*
- This histological description is characteristic of **papillary thyroid carcinoma**, specifically the **"orphan Annie eye" nuclei** often seen.
- While thyroid tissue is involved, the overall clinical presentation (young child, symptomatic, recent infection, movable midline mass) is inconsistent with a malignant thyroid lesion.
*Diffuse hyperplasia and hypertrophy of follicular cells*
- This description is typical of **Graves' disease** or other causes of **diffuse goiter** due to **thyroid hyperactivity**.
- The patient presents with a focal swelling rather than diffuse thyroid enlargement, and there are no signs of hyperthyroidism.
*Cyst-like structure lined by stratified squamous epithelium and containing mucoid material*
- This histology is characteristic of a **branchial cleft cyst**, which typically presents as a **lateral neck mass** (not midline).
- Branchial cleft cysts are derived from remnants of the branchial arches and usually contain mucoid material, sometimes with squamous epithelium, but their location differs.
Question 33: A 50-year-old female presents to her physician with vesicles and tense blisters across her chest, arms, and the back of her shoulders. Physical examination reveals that blistering is not present in her oral mucosa, and the epidermis does not separate upon light stroking of the skin. The patient most likely suffers from a hypersensitivity reaction located:
A. Linearly along the epidermal basement membrane (Correct Answer)
B. In fat cells beneath the skin
C. In nuclei within epidermal cells
D. In net-like patterns around epidermal cells
E. In granular deposits at the tips of dermal papillae
Explanation: ***Linearly along the epidermal basement membrane***
- The description of **tense blisters** and the absence of **Nikolsky's sign** (no epidermal separation with light stroking) are characteristic features of **bullous pemphigoid**.
- **Bullous pemphigoid** is an autoimmune disease where autoantibodies target components of the **hemidesmosomes** located along the **epidermal basement membrane**, leading to subepidermal blistering.
*In fat cells beneath the skin*
- This description is not consistent with any common blistering disorder, and **fat cells** (adipocytes) are not primary targets for blistering in autoimmune diseases.
- Blistering disorders typically involve the epidermis or the dermal-epidermal junction, not the subcutaneous fat.
*In nuclei within epidermal cells*
- Autoantibodies targeting **nuclear antigens** are associated with conditions like **lupus erythematosus**, but this generally leads to characteristic skin rashes, not tense blistering.
- Blistering from nuclear involvement is uncommon and does not match the clinical presentation of bullous pemphigoid or pemphigus.
*In net-like patterns around epidermal cells*
- This pattern of antibody deposition is characteristic of **pemphigus vulgaris**, where autoantibodies target **desmogleins** in the intercellular spaces of the epidermis.
- Pemphigus vulgaris typically presents with **flaccid blisters** that are easily rupturable, and often involves the **oral mucosa**, in contrast to the patient's presentation.
*In granular deposits at the tips of dermal papillae*
- This pattern of IgA deposition, particularly in a granular fashion at the **dermal papillae tips**, is characteristic of **dermatitis herpetiformis**.
- Dermatitis herpetiformis typically presents with **pruritic papules and vesicles**, often on extensor surfaces, and is commonly associated with **celiac disease**, which is not indicated here.
Question 34: A 6-year-old boy is brought to the emergency department due to a severe infection. Laboratory work shows leukocytosis of 60 × 109/L with marked left shift, but no blast cells. The patient is febrile and dehydrated. The physician believes that this is a severe reaction to the infection and orders a leukocyte alkaline phosphatase (LAP) stain on a peripheral smear. The LAP score is elevated. Which of the following statements best describes an additional characteristic of the condition this child is suffering from?
A. Chemotherapy is the treatment of choice.
B. Myeloblasts and promyelocytes are expected to be found.
C. This condition can lead to chronic myelocytic leukemia.
D. A blood count will contain band forms, metamyelocytes, and myelocytes. (Correct Answer)
E. The patient may develop anemia secondary to infection.
Explanation: ***A blood count will contain band forms, metamyelocytes, and myelocytes.***
- Leukocytosis with a **marked left shift** and **elevated LAP score** in the setting of severe infection is characteristic of a **leukemoid reaction**.
- A leukemoid reaction involves the premature release of immature myeloid forms such as **band forms, metamyelocytes, and myelocytes** into the peripheral blood, mimicking leukemia.
*Chemotherapy is the treatment of choice.*
- **Chemotherapy** is typically used to treat malignancies like leukemia, not a **leukemoid reaction**, which is a reactive process to severe infection.
- The primary treatment for a leukemoid reaction is to address the **underlying infection**.
*Myeloblasts and promyelocytes are expected to be found.*
- While there is a left shift, the question explicitly states "no blast cells," which differentiates a **leukemoid reaction** from acute leukemia.
- **Myeloblasts** and **promyelocytes** are more characteristic of acute myeloid leukemia, where they constitute a significant percentage of cells.
*This condition can lead to chronic myelocytic leukemia.*
- A **leukemoid reaction** is a reactive process to infection and does not transform into **chronic myelocytic leukemia (CML)**.
- CML is a myeloproliferative neoplasm characterized by the **BCR-ABL1 fusion gene** and a typically low LAP score, unlike the elevated LAP score seen here.
*The patient may develop anemia secondary to infection.*
- While **anemia of chronic disease** can occur with severe or prolonged infections, it is not the **additional characteristic** that best describes the leukemoid reaction itself, which primarily refers to the white blood cell changes.
- The prominent feature described is the specific reactive pattern of **leukocytosis** and **left shift**.
Question 35: A 40-year-old man presents with a swollen left big toe that started this morning. The patient states that he attended a party last night and drank 4 glasses of whiskey. He denies any trauma to the foot. The patient has a history of similar episodes in the past that were related to alcohol use. His symptoms were previously relieved with ibuprofen. However, the pain persisted despite treatment with the medication. Physical examination reveals a tender and erythematous, swollen left 1st metatarsophalangeal joint. Which of the following events most likely contributed to his condition?
A. Upregulation of cellular adhesion molecules to promote neutrophil migration (Correct Answer)
B. Downregulation of integrins in the neutrophils
C. Vasoconstriction
D. Activation of cytosolic caspases
E. Decreased expression of selectin in the endothelium
Explanation: ***Upregulation of cellular adhesion molecules to promote neutrophil migration***
- This scenario describes an acute **gout attack**, characterized by severe inflammation in the **first metatarsophalangeal joint** (podagra) triggered by **alcohol intake**.
- **Neutrophil migration** orchestrated by upregulated **cellular adhesion molecules** (e.g., selectins, integrins) is a central mechanism in acute gout, as neutrophils phagocytose **monosodium urate crystals**, leading to the release of inflammatory mediators.
*Downregulation of integrins in the neutrophils*
- **Downregulation of integrins** would impair neutrophil adhesion and migration into the inflamed joint, thereby **reducing** the inflammatory response, which contradicts the presented symptoms of severe inflammation.
- Integrins are crucial for stable adhesion and **transmigration** of neutrophils through the endothelium.
*Vasoconstriction*
- **Vasoconstriction** would lead to reduced blood flow and typically present as **pallor** and **coldness** in the affected area, rather than the observed **erythema** and swelling characteristic of inflammation.
- Acute inflammation, as seen in gout, is primarily associated with **vasodilation**, increasing blood flow to the site.
*Activation of cytosolic caspases*
- **Activation of cytosolic caspases** is a hallmark of **apoptosis** (programmed cell death), which is not the primary event driving the acute inflammatory response in gout.
- While cell death can occur in inflammatory processes, the immediate cause of the excruciating pain and swelling in gout is the **inflammatory cascade** from crystal deposition.
*Decreased expression of selectin in the endothelium*
- **Decreased expression of selectin** on endothelial cells would hinder the initial "rolling" adhesion of neutrophils to the vessel wall, thereby **reducing** neutrophil recruitment and inflammatory exudation.
- In acute inflammation, **selectin expression is upregulated** to facilitate the early stages of leukocyte extravasation.
Question 36: A 42-year-old woman with well-controlled HIV on antiretroviral therapy comes to the physician because of a 2-week history of a painless lesion on her right calf. Many years ago, she had a maculopapular rash over her trunk, palms, and soles that resolved spontaneously. Physical examination shows a 4-cm firm, non-tender, indurated ulcer with a moist, dark base and rolled edges. There is a similar lesion at the anus. Results of rapid plasma reagin testing are positive. Which of the following findings is most likely on microscopic examination of these lesions?
A. Epithelioid cell infiltrate surrounding acellular, granular core
B. Ulcerated epidermis with plasma cell infiltrate (Correct Answer)
C. Epidermal hyperplasia with dermal lymphocytic infiltrate
D. Lichenoid hyperplasia with superficial neutrophilic infiltrate
E. Coagulative necrosis surrounded by fibroblast and macrophage infiltrate
Explanation: ***Ulcerated epidermis with plasma cell infiltrate***
- The patient's history of a prior maculopapular rash involving palms and soles (secondary syphilis), current presentation of **painless, indurated ulcers with rolled edges** (gummas), and **positive RPR test** are diagnostic of **tertiary syphilis**.
- **Gummas** are granulomatous lesions with coagulative necrosis, but the histologic **hallmark** that distinguishes syphilitic lesions from other granulomatous diseases is the **prominent plasma cell infiltrate** in the dermis beneath the **ulcerated epidermis**.
- **Obliterative endarteritis** is also characteristic of syphilis at any stage.
*Coagulative necrosis surrounded by fibroblast and macrophage infiltrate*
- While gummas do contain **coagulative necrosis** surrounded by granulomatous inflammation, this description alone is **non-specific** and could describe many types of granulomas.
- The distinguishing feature of syphilitic gummas is the **dense plasma cell infiltrate**, which is not captured in this option.
- Without mentioning plasma cells, this description could apply to granulomas from tuberculosis, foreign body reactions, or other causes.
*Epithelioid cell infiltrate surrounding acellular, granular core*
- This describes a **tuberculoid (caseating) granuloma** characteristic of **tuberculosis** or **sarcoidosis**.
- While syphilis can show granulomatous inflammation, the absence of plasma cells in this description makes it incorrect.
- The "acellular, granular core" suggests caseous necrosis, which is more typical of TB than syphilis.
*Lichenoid hyperplasia with superficial neutrophilic infiltrate*
- **Lichenoid reactions** show a band-like lymphocytic infiltrate at the dermo-epidermal junction, seen in conditions like **lichen planus** or drug reactions.
- **Neutrophilic infiltrates** suggest acute bacterial infections or neutrophilic dermatoses like **pyoderma gangrenosum**, not chronic spirochete infection.
- This does not describe syphilitic histology.
*Epidermal hyperplasia with dermal lymphocytic infiltrate*
- This is a **non-specific** finding seen in various chronic inflammatory skin conditions like **chronic eczema** or **psoriasis**.
- It lacks the specific features of syphilis, particularly the **prominent plasma cells** and granulomatous inflammation with necrosis.
- This description is too generic to identify syphilitic gummas.
Question 37: A 10-year-old boy presents with sudden shortness of breath. The patient’s mother says he was playing in the school garden 2 hours ago and suddenly started to complain of abdominal pain and vomited a few times. An hour later, he slowly developed a rash that involved his chest, arms, and legs, and his breathing became faster, with audible wheezing. He has no significant past medical history. His temperature is 37.0°C (98.6°F), blood pressure is 100/60 mm Hg, pulse is 130/min, and respirations are 25/min. On physical examination, there is a rash on his right arm (shown in the image, below). Which of the following cells will mainly be found in this patient if a histological sample is taken from the site of the skin lesion 4 hours from now?
A. Plasma cells
B. Basophils
C. Eosinophils (Correct Answer)
D. Mast cells
E. Neutrophils
Explanation: ***Eosinophils***
- This patient is experiencing an **acute Type I hypersensitivity reaction** (IgE-mediated allergic reaction) after exposure to an allergen in the school garden, presenting with urticaria, wheezing, and systemic symptoms.
- The reaction has two phases: the **immediate phase** (0-30 minutes) involves mast cell degranulation releasing histamine, and the **late phase** (4-24 hours) is characterized by recruitment of **eosinophils** to the site of inflammation.
- At **4 hours after the initial exposure**, a histological sample from the skin lesion would show predominant **eosinophil infiltration**, which is the hallmark of the late-phase allergic response along with basophils and lymphocytes.
- Eosinophils release major basic protein, eosinophil cationic protein, and leukotrienes that contribute to tissue damage and prolonged inflammation in allergic reactions.
*Plasma cells*
- **Plasma cells** produce and secrete antibodies and are found in chronic inflammation or secondary immune responses, not in the acute cellular infiltrate of an allergic reaction within hours.
- While IgE antibodies (produced by plasma cells earlier) trigger mast cell degranulation, plasma cells themselves are not the predominant cell type in acute allergic skin lesions.
*Mast cells*
- **Mast cells** initiate the immediate hypersensitivity reaction through degranulation and histamine release.
- They are most active in the **immediate phase** (0-30 minutes), not the predominant infiltrating cell type at 4-6 hours post-exposure.
- While present in tissue, the question asks about cells found "4 hours from now," which corresponds to the late-phase response dominated by eosinophils.
*Basophils*
- **Basophils** are circulating granulocytes that can infiltrate tissue during late-phase allergic reactions and release histamine similar to mast cells.
- While they are present in the late phase, **eosinophils** are significantly more numerous and characteristic of the late-phase allergic response at 4-6 hours.
*Neutrophils*
- **Neutrophils** are the hallmark of acute bacterial infections, tissue necrosis, and early acute inflammation (first 6-24 hours in bacterial infections).
- In **allergic/hypersensitivity reactions**, neutrophils are NOT the predominant cell type; the inflammatory infiltrate is characterized by eosinophils, basophils, and lymphocytes.
- This patient's presentation (urticaria, wheezing, exposure to outdoor allergen) indicates a Type I hypersensitivity reaction, not a neutrophil-mediated inflammatory process.
Question 38: A 27-year-old man comes to the physician because of multiple, dry, scaly lesions on his elbows. The lesions appeared 4 months ago and have progressively increased in size. They are itchy and bleed when he scratches them. There is no associated pain or discharge. He was diagnosed with HIV infection 6 years ago. He has smoked a pack of cigarettes daily for the past 10 years. Current medications include raltegravir, lamivudine, abacavir, and cotrimoxazole. An image of the lesions is shown. His CD4+ T-lymphocyte count is 470/mm3 (normal ≥ 500). Which of the following is the most likely cause of this patient's skin findings?
A. Neoplastic T-cell Infiltration
B. HPV-2 infection
C. Autoimmune melanocyte destruction
D. Malassezia furfur infection
E. Increased keratinocyte proliferation (Correct Answer)
Explanation: ***Increased keratinocyte proliferation***
- The patient's symptoms (dry, scaly, itchy lesions on elbows, bleeding when scratched) are classic for **psoriasis**. Psoriasis is caused by excessive **keratinocyte proliferation** and dysfunctional epidermal differentiation, leading to thickened, scaling plaques.
- HIV infection is a risk factor for developing or exacerbating psoriasis, even with a relatively preserved CD4+ count, due to immune dysregulation. The absence of pain or discharge further supports a non-infectious, proliferative process.
*Neoplastic T-cell Infiltration*
- This description is characteristic of **mycosis fungoides**, a cutaneous T-cell lymphoma, which can present as scaly patches or plaques. However, mycosis fungoides typically has a more insidious course and is less commonly associated with significant itching and bleeding upon scratching, unless advanced.
- While HIV can increase some cancer risks, the classic psoriatic symptoms, rather than specific features of cutaneous lymphoma, point away from this diagnosis.
*HPV-2 infection*
- **Human papillomavirus (HPV) type 2** commonly causes **warts (verruca vulgaris)**, which are typically flesh-colored, raised papules with a rough, verrucous surface.
- Warts are generally non-itchy and do not characteristically bleed with scratching in the same manner as psoriasis. The description of dry, scaly lesions on the elbows is not typical for HPV-2.
*Autoimmune melanocyte destruction*
- **Autoimmune melanocyte destruction** is the underlying mechanism of **vitiligo**, which presents as well-demarcated, depigmented (white) patches on the skin.
- This condition involves loss of skin pigment and would not cause dry, scaly, itchy, or bleeding lesions.
*Malassezia furfur infection*
- **Malassezia furfur** is a yeast associated with **tinea versicolor** and **seborrheic dermatitis**. Tinea versicolor presents as hypo- or hyperpigmented macules, often on the trunk, with fine scale.
- Seborrheic dermatitis typically affects sebum-rich areas (scalp, face, chest) with greasy, yellow scales. Neither condition produces the thick, dry, silvery scales classically seen on elbows, which bleed when scratched, as described.
Question 39: A 37-year-old woman presents to the occupational health clinic for a new employee health screening. She has limited medical records prior to her immigration to the United States several years ago. She denies any current illness or significant medical history. Purified protein derivative (PPD) is injected on the inside of her left forearm for tuberculosis (TB) screening. Approximately 36 hours later, the patient comes back to the occupational health clinic and has an indurated lesion with bordering erythema measuring 15 mm in diameter at the site of PPD injection. Of the following options, which is the mechanism of her reaction?
A. Type III and IV–mixed immune complex and cell-mediated hypersensitivity reactions
B. Type III–immune complex-mediated hypersensitivity reaction
C. Type I–anaphylactic hypersensitivity reaction
D. Type II–cytotoxic hypersensitivity reaction
E. Type IV–cell-mediated (delayed) hypersensitivity reaction (Correct Answer)
Explanation: ***Type IV–cell-mediated (delayed) hypersensitivity reaction***
- The **PPD test** for tuberculosis is a classic example of a **Type IV hypersensitivity reaction**, also known as **delayed-type hypersensitivity (DTH)**. This reaction is orchestrated by **T lymphocytes** (specifically CD4+ T cells) that recognize antigens presented by antigen-presenting cells
- The **induration** at 36 hours is a hallmark of this type of reaction, as it typically peaks between **24 to 72 hours** after antigen exposure, reflecting the time required for T cells to migrate to the site and initiate an inflammatory response. The immune response involves the release of **cytokines** leading to macrophage accumulation and localized tissue damage.
*Type III and IV–mixed immune complex and cell-mediated hypersensitivity reactions*
- While immune complexes (Type III) and cell-mediated reactions (Type IV) can both lead to tissue damage, a PPD test is primarily a **cell-mediated response** and is not characterized by significant immune complex deposition.
- Mixed reactions are less common and usually involve a sustained presence of antigen leading to both types of responses, which is not the typical mechanism for an acute PPD skin test.
*Type III–immune complex-mediated hypersensitivity reaction*
- **Type III hypersensitivity** is characterized by the formation of **antigen-antibody immune complexes** that deposit in tissues, leading to inflammation and tissue damage, often seen in conditions like serum sickness or lupus nephritis.
- The PPD reaction is based on T-cell recognition of mycobacterial antigens, not the deposition of soluble antigen-antibody complexes.
*Type I–anaphylactic hypersensitivity reaction*
- **Type I hypersensitivity** is an **immediate allergic reaction** mediated by **IgE antibodies** binding to mast cells and basophils, leading to histamine release upon re-exposure to an allergen.
- This type of reaction typically occurs within minutes of exposure, not 36 hours later, and presents with symptoms like hives, angioedema, or anaphylaxis.
*Type II–cytotoxic hypersensitivity reaction*
- **Type II hypersensitivity** involves **antibodies (IgG or IgM)** binding to antigens on the surface of **host cells**, leading to cell lysis or dysfunction, often seen in transfusion reactions or autoimmune hemolytic anemia.
- The PPD test does not involve direct antibody-mediated destruction of host cells.
Question 40: A 22-year-old woman comes to the physician because of pain and swelling of her left foot. Three days ago, she cut her foot on an exposed rock at the beach. Her temperature is 37.7°C (100°F). Examination of the left foot shows edema around a fluctuant erythematous lesion on the lateral foot. Which of the following is most likely the primary mechanism for the development of edema in this patient?
A. Decreased plasma oncotic pressure
B. Fluid production by bacteria
C. Increased capillary hydrostatic pressure
D. Separation of endothelial junctions (Correct Answer)
E. Systemic cytokine release
Explanation: ***Separation of endothelial junctions***
- The **cut to the foot** likely introduced bacteria, leading to a localized infection evident by the **erythematous, fluctuant lesion** and low-grade fever.
- During **inflammation**, chemical mediators (like histamine and bradykinin) cause **endothelial cells to contract**, leading to the widening of inter-endothelial junctions, increasing **vascular permeability** and allowing fluid and proteins to leak into the interstitial space, causing edema.
*Decreased plasma oncotic pressure*
- This typically occurs in systemic conditions such as **liver failure** (decreased albumin production), **nephrotic syndrome** (protein loss in urine), or **severe malnutrition**.
- There is no clinical evidence in the patient's presentation to suggest any of these systemic conditions are present.
*Fluid production by bacteria*
- While some bacteria can produce toxins or metabolic byproducts that contribute to inflammation, the **direct production of significant interstitial fluid** by bacteria themselves is not the primary mechanism of edema in bacterial infections.
- Bacterial action primarily triggers the host's inflammatory response, which then leads to fluid accumulation.
*Increased capillary hydrostatic pressure*
- This typically results from **impaired venous return** (e.g., deep vein thrombosis, heart failure) or **arteriolar dilation**.
- While local vasodilation occurs in inflammation, the primary mechanism of edema in localized infection is increased vascular permeability due to endothelial changes, not solely elevated hydrostatic pressure.
*Systemic cytokine release*
- While systemic cytokine release (e.g., in sepsis) can lead to **systemic capillary leak syndrome** and generalized edema, the patient's presentation describes a **localized infection** with localized edema.
- The fever (37.7°C) is mild, suggesting a localized rather than severe systemic inflammatory response at this stage.
