A 19-year-old woman presents to the family medical center with a 2-week history of a sore throat. She says that she has felt increasingly tired during the day and has a difficult time staying awake during her classes at the university. She appears well-nourished with a low energy level. Her vital signs include the following: the heart rate is 82/min, the respiratory rate is 14/min, the temperature is 37.8°C (100.0°F), and the blood pressure is 112/82 mm Hg. Inspection of the pharynx is depicted in the picture. Palpation of the neck reveals posterior cervical lymphadenopathy. The membrane does not bleed upon scraping. What is the most specific finding for detecting the syndrome described in the vignette?
Q72
A 47-year-old male presents to the emergency department with facial swelling and trouble breathing. These symptoms began this morning and progressively worsened over the past several hours. Vital signs are as follows: T 37.7, HR 108, BP 120/76, RR 20, and SpO2 96%. Physical examination reveals nonpitting swelling of the face, hands, and arms as well as edema of the tongue and mucus membranes of the mouth and pharynx. The patient reports several episodes of mild facial swelling that occurred during childhood between the ages of 5-18, but he does not recall seeing a physician or receiving treatment for this. His medical history is otherwise negative, except for mild hypertension for which his primary care physician initiated lisinopril 2 weeks ago. This patient most likely has which of the following underlying abnormalities?
Q73
A 23-year-old woman presents with progressively worsening headache, photophobia, and intermittent fever that have lasted for 6 days. She says her headache is mostly frontal and radiates down her neck. She denies any recent history of blood transfusions, recent travel, or contact with animals. Her past medical history is unremarkable. She is sexually active with a single partner for the past 3 years. Her temperature is 38.5°C (101.3°F). On physical examination, she appears pale and diaphoretic. A fine erythematous rash is noted on the neck and forearms. A lumbar puncture is performed and CSF analysis reveals:
Opening pressure: 300 mm H2O
Erythrocytes: None
Leukocytes: 72/mm3
Neutrophils: 10%
Lymphocytes: 75%
Mononuclear: 15%
Protein: 100 mg/dL
Glucose: 70 mg/dL
Which of the following is the most likely diagnosis in this patient?
Q74
A 5-year-old boy presents with bilateral conjunctivitis and pharyngitis. The patient’s mother says that symptoms acutely onset 3 days ago and include itchy red eyes, a low-grade fever, and a sore throat. She says that the patient recently attended a camp where other kids were also ill and were completely healthy before going. No significant past medical history. Which of the following is the most likely cause of this patient’s symptoms?
Q75
A previously healthy 10-year-old girl is brought to the physician because of severe malaise, pink eyes, cough, and a runny nose for 3 days. She recently immigrated from Sudan and immunization records are unavailable. Her temperature is 40.1°C (104.1°F). Examination shows bilateral conjunctival injections. There are multiple bluish-gray lesions on an erythematous buccal mucosa and soft palate. This patient is at increased risk for which of the following complications?
Q76
A parent presents to her pediatrician requesting information about immunizations for her newborn. The pediatrician explains about basic principles of immunization, types of vaccines, possible adverse effects, and the immunization schedule. Regarding how immunizations work, the pediatrician explains that there are mainly 2 types of vaccines. The first type of vaccine provides stronger and more lasting immunity as it induces both cellular and humoral immune responses. The second type of vaccine produces mainly a humoral response only, and its overall efficacy is less as compared to the first type. Which of the following vaccines belongs to the first type of vaccine that the pediatrician is talking about?
Q77
A 17-year-old boy is admitted to the emergency department with a history of fatigue, fever of 40.0°C (104.0°F), sore throat, and enlarged cervical lymph nodes. On physical examination, his spleen and liver are not palpable. A complete blood count is remarkable for atypical reactive T cells. An examination of his tonsils is shown in the image below. Which of the following statements is true about the condition of this patient?
Q78
A 5-year-old boy presents to your office with his mother. The boy has been complaining of a sore throat and headache for the past 2 days. His mother states that he had a fever of 39.3°C (102.7°F) and had difficulty eating. On examination, the patient has cervical lymphadenopathy and erythematous tonsils with exudates. A streptococcal rapid antigen detection test is negative. Which of the following is the most likely causative agent?
Q79
A 30-year-old man presents with fever, malaise, and severe pain in his right wrist and left knee for the last 2 days. He describes the pain as 8/10 in intensity, sharp in character, and extending from his right wrist to his fingers. He denies any recent inciting trauma or similar symptoms in the past. His past medical history is unremarkable. He is sexually active with multiple partners and uses condoms inconsistently. The vital signs include blood pressure 120/70 mm Hg, pulse 100/min, and temperature 38.3°C (101.0°F). On physical examination, the right wrist and left knee joints are erythematous, warm, and extremely tender to palpation. Both joints have a significantly restricted range of motion. A petechial rash is noted on the right forearm. An arthrocentesis is performed on the left knee joint. Which of the following would be the most likely finding in this patient?
Q80
An 82-year-old woman is brought to the physician by her daughter because of a 3-day history of a runny nose, headache, and cough. The patient's grandson recently had similar symptoms. Her vital signs are within normal limits. Pulse oximetry on room air shows an oxygen saturation of 99%. Lungs are clear to auscultation. Testing of nasal secretions is performed to identify the viral strain. Electron microscopy shows a non-enveloped RNA virus with an icosahedral capsid. Binding to which of the following is responsible for the virulence of this virus?
Viruses US Medical PG Practice Questions and MCQs
Question 71: A 19-year-old woman presents to the family medical center with a 2-week history of a sore throat. She says that she has felt increasingly tired during the day and has a difficult time staying awake during her classes at the university. She appears well-nourished with a low energy level. Her vital signs include the following: the heart rate is 82/min, the respiratory rate is 14/min, the temperature is 37.8°C (100.0°F), and the blood pressure is 112/82 mm Hg. Inspection of the pharynx is depicted in the picture. Palpation of the neck reveals posterior cervical lymphadenopathy. The membrane does not bleed upon scraping. What is the most specific finding for detecting the syndrome described in the vignette?
A. > 10% atypical lymphocytes
B. Positive rapid strep test
C. Growth in Loffler’s medium
D. Increased transaminase levels
E. Positive monospot test (Correct Answer)
Explanation: ***Positive monospot test***
- The patient's symptoms (sore throat, fatigue, posterior cervical lymphadenopathy, pharyngitis with exudates, age) are highly suggestive of **infectious mononucleosis**, which is caused by the **Epstein-Barr virus (EBV)**.
- A **positive monospot test**, which detects **heterophile antibodies**, is the most specific and widely used rapid diagnostic test for infectious mononucleosis.
* > 10% atypical lymphocytes*
- While **atypical lymphocytes** are characteristic of infectious mononucleosis, they are not exclusive to EBV infection and can be seen in other viral infections (e.g., CMV, HIV). Therefore, this finding is less specific than a positive monospot test.
- A definitive diagnosis usually requires a combination of clinical symptoms and specific serological tests like the **monospot test** or **EBV-specific antibodies**.
*Positive rapid strep test*
- A rapid strep test detects **Group A Streptococcus (GAS)**. While bacterial pharyngitis can present with a sore throat, the accompanying fatigue and posterior cervical lymphadenopathy make streptococcal pharyngitis less likely as the primary diagnosis.
- The rapid strep test would be negative in infectious mononucleosis, and therefore, a positive result would rule out mononucleosis as the sole cause.
*Growth in Loffler’s medium*
- **Loffler's medium** is used to culture **Corynebacterium diphtheriae**, the causative agent of diphtheria. Diphtheria presents with a severe sore throat and a tenacious gray membrane that **bleeds upon scraping**, unlike the description in the vignette.
- While it's a specific diagnostic test for diphtheria, the patient's presentation does not align with diphtheria, and this test would not be positive in infectious mononucleosis.
*Increased transaminase levels*
- **Increased transaminase levels** (AST, ALT) indicate liver involvement, which can occur in infectious mononucleosis due to **hepatitis**.
- While this is a common finding in many cases of mononucleosis (and supports the diagnosis), it is an indicator of organ involvement rather than a specific diagnostic test for the presence of the virus or its unique immunological response (like the monospot test).
Question 72: A 47-year-old male presents to the emergency department with facial swelling and trouble breathing. These symptoms began this morning and progressively worsened over the past several hours. Vital signs are as follows: T 37.7, HR 108, BP 120/76, RR 20, and SpO2 96%. Physical examination reveals nonpitting swelling of the face, hands, and arms as well as edema of the tongue and mucus membranes of the mouth and pharynx. The patient reports several episodes of mild facial swelling that occurred during childhood between the ages of 5-18, but he does not recall seeing a physician or receiving treatment for this. His medical history is otherwise negative, except for mild hypertension for which his primary care physician initiated lisinopril 2 weeks ago. This patient most likely has which of the following underlying abnormalities?
A. Deficiency of C1 esterase inhibitor (Correct Answer)
B. Lack of NADPH oxidase
C. MHC class I deficiency
D. Defect in cytoskeletal glycoprotein
E. Defective lysosomal storage proteins
Explanation: ***Deficiency of C1 esterase inhibitor***
- The patient's history of **recurrent angioedema** since childhood, nonpitting edema, and the current presentation with **facial and airway swelling** after starting an ACE inhibitor (lisinopril) are classic signs of **hereditary angioedema (HAE)**, which is caused by a C1 esterase inhibitor deficiency.
- C1 esterase inhibitor normally regulates the **bradykinin pathway** and the complement system; a deficiency leads to uncontrolled bradykinin production, resulting in increased vascular permeability and angioedema.
*Lack of NADPH oxidase*
- This deficiency causes **chronic granulomatous disease**, characterized by recurrent severe infections, particularly with catalase-positive organisms.
- It does not present with isolated angioedema.
*MHC class I deficiency*
- This is a rare primary immunodeficiency presenting with recurrent viral infections, particularly respiratory viruses, and **CD8 T-cell lymphopenia**.
- It does not typically cause angioedema.
*Defect in cytoskeletal glycoprotein*
- Defects in cytoskeletal glycoproteins are associated with various disorders, such as certain types of **muscular dystrophy** or **junctional epidermolysis bullosa**, depending on the specific protein involved.
- These conditions do not manifest as isolated angioedema.
*Defective lysosomal storage proteins*
- Defective lysosomal storage proteins lead to **lysosomal storage disorders**, which are a group of metabolic diseases characterized by the accumulation of undigested or partially digested macromolecules within lysosomes.
- These disorders present with a wide range of symptoms, including neurological dysfunction, organomegaly, and skeletal abnormalities, but not angioedema.
Question 73: A 23-year-old woman presents with progressively worsening headache, photophobia, and intermittent fever that have lasted for 6 days. She says her headache is mostly frontal and radiates down her neck. She denies any recent history of blood transfusions, recent travel, or contact with animals. Her past medical history is unremarkable. She is sexually active with a single partner for the past 3 years. Her temperature is 38.5°C (101.3°F). On physical examination, she appears pale and diaphoretic. A fine erythematous rash is noted on the neck and forearms. A lumbar puncture is performed and CSF analysis reveals:
Opening pressure: 300 mm H2O
Erythrocytes: None
Leukocytes: 72/mm3
Neutrophils: 10%
Lymphocytes: 75%
Mononuclear: 15%
Protein: 100 mg/dL
Glucose: 70 mg/dL
Which of the following is the most likely diagnosis in this patient?
A. Lymphocytic choriomeningitis virus
B. Ehrlichiosis
C. Enterovirus meningitis (Correct Answer)
D. Brucellosis
E. Mumps meningitis
Explanation: ***Enterovirus meningitis***
- The patient's symptoms of **headache**, **photophobia**, **fever**, and a **fine erythematous rash**, combined with CSF findings of **lymphocytic pleocytosis (75%)**, **elevated protein**, and **normal glucose**, are classic for **viral (aseptic) meningitis**.
- Enteroviruses (including coxsackievirus and echovirus) are the **most common cause** of viral meningitis in immunocompetent adults, particularly in summer and fall.
- The **normal glucose level** (70 mg/dL) effectively rules out bacterial meningitis, while the **lymphocytic predominance** with mildly elevated protein is pathognomonic for viral etiology.
- The fine erythematous rash is consistent with enteroviral exanthem.
*Lymphocytic choriomeningitis virus*
- While LCMV can cause aseptic meningitis with similar CSF findings (lymphocytic pleocytosis, normal glucose), it is typically acquired through contact with **rodent urine or feces**, particularly from pet hamsters or mice.
- The patient **denies animal contact**, making this diagnosis less likely than the more prevalent enterovirus infection.
*Ehrlichiosis*
- Ehrlichiosis is a **tick-borne illness** (from *Ehrlichia* species) that can cause fever, headache, and rash, but typically presents with **leukopenia**, **thrombocytopenia**, and elevated liver enzymes.
- The rash in ehrlichiosis is often petechial or absent entirely. CNS involvement is uncommon and would more likely present as meningoencephalitis rather than isolated meningitis.
- The CSF profile with prominent lymphocytic pleocytosis and normal glucose fits viral meningitis better than ehrlichiosis.
*Brucellosis*
- Brucellosis is a **zoonotic infection** acquired through contact with **unpasteurized dairy products** or infected livestock (cattle, goats, pigs), which the patient denies.
- While *Brucella* can cause chronic meningitis with lymphocytic pleocytosis, it classically presents with **undulating fever**, hepatosplenomegaly, and a more protracted course (weeks to months).
- The acute 6-day presentation without exposure history makes this unlikely.
*Mumps meningitis*
- Mumps virus can cause aseptic meningitis with a similar CSF profile (lymphocytic pleocytosis, normal glucose).
- However, mumps meningitis typically occurs in association with or following **parotitis (parotid gland swelling)**, which is not mentioned in this case.
- With widespread MMR vaccination, mumps is now rare in immunized populations, making enterovirus a more likely diagnosis.
Question 74: A 5-year-old boy presents with bilateral conjunctivitis and pharyngitis. The patient’s mother says that symptoms acutely onset 3 days ago and include itchy red eyes, a low-grade fever, and a sore throat. She says that the patient recently attended a camp where other kids were also ill and were completely healthy before going. No significant past medical history. Which of the following is the most likely cause of this patient’s symptoms?
A. Influenza virus
B. Adenovirus (Correct Answer)
C. Metapneumovirus
D. Rhinovirus
E. Enterovirus
Explanation: ***Adenovirus***
- **Adenovirus** commonly causes outbreaks of **conjunctivitis** and **pharyngitis**, often referred to as **pharyngoconjunctival fever**, especially in crowded settings like summer camps.
- The acute onset of symptoms, including itchy red eyes, low-grade fever, and sore throat, in a child who was previously healthy and recently attended a camp with ill children, strongly points to an adenoviral infection.
*Influenza virus*
- Influenza typically presents with more prominent **systemic symptoms** such as high fever, body aches, chills, and productive cough, with conjunctivitis being less common or severe.
- While respiratory symptoms like sore throat can occur, the combination with prominent bilateral conjunctivitis less strongly suggests influenza.
*Metapneumovirus*
- **Metapneumovirus** primarily causes **lower respiratory tract infections**, such as bronchiolitis, pneumonia, and croup, especially in young children and the elderly.
- Conjunctivitis and pharyngitis as primary presenting symptoms are not typical of metapneumovirus infection.
*Rhinovirus*
- **Rhinovirus** is the most common cause of the **common cold**, characterized primarily by rhinorrhea, sneezing, and sore throat.
- While it can cause pharyngitis, conjunctivitis is a less common and less prominent feature compared to what is described in this case.
*Enterovirus*
- **Enteroviruses** can cause a variety of syndromes, including **hand, foot, and mouth disease**, **herpangina**, and aseptic meningitis, which often have specific dermatological or neurological manifestations.
- While some enteroviruses can cause non-specific febrile illness, the classic constellation of bilateral conjunctivitis and pharyngitis as prominently described is less typical of a primary enteroviral infection.
Question 75: A previously healthy 10-year-old girl is brought to the physician because of severe malaise, pink eyes, cough, and a runny nose for 3 days. She recently immigrated from Sudan and immunization records are unavailable. Her temperature is 40.1°C (104.1°F). Examination shows bilateral conjunctival injections. There are multiple bluish-gray lesions on an erythematous buccal mucosa and soft palate. This patient is at increased risk for which of the following complications?
A. Glomerular immune complex deposition
B. Immune thrombocytopenic purpura
C. Subacute sclerosing panencephalitis (Correct Answer)
D. Non-Hodgkin lymphoma
E. Transient arrest of erythropoiesis
Explanation: ***Subacute sclerosing panencephalitis***
- This patient's symptoms (malaise, pink eyes, cough, runny nose, high fever, conjunctival injection, and **Koplik spots** on the buccal mucosa) are highly indicative of **measles** (rubeola) in its prodromal phase.
- **Subacute sclerosing panencephalitis (SSPE)** is a rare, fatal, progressive neurodegenerative disease that occurs years after an initial measles infection due to persistent measles virus infection in the brain.
*Glomerular immune complex deposition*
- While some viral infections can lead to **glomerulonephritis** via immune complex deposition, it is not a direct or common complication of measles itself.
- Measles primarily causes a **rash**, respiratory symptoms, and can lead to complications such as pneumonia or otitis media, but not typically glomerular immune complex deposition.
*Immune thrombocytopenic purpura*
- **ITP** involves the destruction of platelets by autoantibodies and can be triggered by various viral infections (e.g., rubella, varicella, Epstein-Barr virus) in children.
- While theoretically possible with any severe viral infection, ITP is not a particularly common or characteristic complication of measles compared to other well-established sequelae.
*Non-Hodgkin lymphoma*
- Non-Hodgkin lymphoma is a type of cancer that affects lymphocytes and is more commonly associated with conditions like **Epstein-Barr virus**, HIV, or immunosuppression.
- There is **no direct or well-established link** between measles infection and an increased risk of developing Non-Hodgkin lymphoma.
*Transient arrest of erythropoiesis*
- **Transient aplastic crisis** (transient arrest of erythropoiesis) is most commonly associated with **Parvovirus B19 infection**, especially in patients with underlying chronic hemolytic anemias (e.g., sickle cell disease).
- Measles is not typically associated with either significant anemia or a direct arrest of erythropoiesis.
Question 76: A parent presents to her pediatrician requesting information about immunizations for her newborn. The pediatrician explains about basic principles of immunization, types of vaccines, possible adverse effects, and the immunization schedule. Regarding how immunizations work, the pediatrician explains that there are mainly 2 types of vaccines. The first type of vaccine provides stronger and more lasting immunity as it induces both cellular and humoral immune responses. The second type of vaccine produces mainly a humoral response only, and its overall efficacy is less as compared to the first type. Which of the following vaccines belongs to the first type of vaccine that the pediatrician is talking about?
A. Hepatitis A vaccine
B. Polio vaccine (Salk)
C. Yellow fever vaccine (Correct Answer)
D. Rabies vaccine
E. Hepatitis B vaccine
Explanation: ***Yellow fever vaccine***
- The Yellow fever vaccine is a **live-attenuated vaccine**, which mimics natural infection and effectively stimulates both **cellular and humoral immune responses**, leading to strong and long-lasting immunity.
- Live-attenuated vaccines contain a weakened form of the pathogen, allowing for replication within the host and robust immune system activation.
*Hepatitis A vaccine*
- The Hepatitis A vaccine is an **inactivated vaccine**, which primarily induces a **humoral (antibody-mediated) immune response**.
- Inactivated vaccines generally do not stimulate a strong cellular immune response and often require booster doses to maintain protective immunity.
*Polio vaccine (Salk)*
- The Salk polio vaccine is an **inactivated polio vaccine (IPV)**, meaning it contains killed viral particles.
- As an inactivated vaccine, it mainly elicits a **humoral immune response** producing circulating antibodies but less mucosal or cellular immunity.
*Rabies vaccine*
- The Rabies vaccine is an **inactivated vaccine** given after exposure or for pre-exposure prophylaxis.
- It primarily induces a **humoral antibody response** rather than a strong cellular immune response.
*Hepatitis B vaccine*
- The Hepatitis B vaccine is a **recombinant vaccine**, containing only a portion of the viral antigen (HBsAg).
- This type of vaccine primarily stimulates a **humoral immune response** leading to antibody production, which is effective but does not typically induce a strong cellular response like live vaccines.
Question 77: A 17-year-old boy is admitted to the emergency department with a history of fatigue, fever of 40.0°C (104.0°F), sore throat, and enlarged cervical lymph nodes. On physical examination, his spleen and liver are not palpable. A complete blood count is remarkable for atypical reactive T cells. An examination of his tonsils is shown in the image below. Which of the following statements is true about the condition of this patient?
A. The infectious organism can become latent in macrophages.
B. The infectious organism is heterophile-negative.
C. Splenomegaly is a rare finding.
D. The infectious organism causes Cutaneous T-cell lymphoma.
E. The infectious organism can become latent in B cells. (Correct Answer)
Explanation: ***The infectious organism can become latent in B cells.***
- The patient's symptoms (fatigue, fever, sore throat, enlarged cervical lymph nodes, atypical reactive T cells) are classic for **infectious mononucleosis**, which is most commonly caused by the **Epstein-Barr virus (EBV)**.
- EBV primarily infects **B lymphocytes** and establishes latency within these cells, enabling persistent infection and intermittent reactivation.
*The infectious organism can become latent in macrophages.*
- While some viruses can establish latency in macrophages (e.g., HIV), **Epstein-Barr virus** primarily targets and establishes latency in **B lymphocytes**, not macrophages.
- Macrophages play a role in the immune response to EBV, but they are not the primary site of viral latency.
*The infectious organism is heterophile-negative.*
- Infectious mononucleosis caused by EBV is typically associated with a **positive heterophile antibody test**, which detects specific antibodies produced in response to the infection.
- A heterophile-negative mononucleosis-like illness might suggest other causes like cytomegalovirus (CMV), but the classic presentation points to EBV.
*Splenomegaly is a rare finding.*
- **Splenomegaly** is a **common finding** in infectious mononucleosis, occurring in 50-75% of patients.
- Although the spleen was not palpable in this specific patient, its absence on physical exam does not make splenomegaly a rare feature of the disease overall.
*The infectious organism causes Cutaneous T-cell lymphoma.*
- The infectious organism (EBV) is associated with several malignancies, including **Burkitt lymphoma**, **nasopharyngeal carcinoma**, and Hodgkin lymphoma, primarily involving B cells or epithelial cells.
- **Cutaneous T-cell lymphoma** is a type of non-Hodgkin lymphoma that primarily affects T lymphocytes and is not directly caused by EBV.
Question 78: A 5-year-old boy presents to your office with his mother. The boy has been complaining of a sore throat and headache for the past 2 days. His mother states that he had a fever of 39.3°C (102.7°F) and had difficulty eating. On examination, the patient has cervical lymphadenopathy and erythematous tonsils with exudates. A streptococcal rapid antigen detection test is negative. Which of the following is the most likely causative agent?
A. A gram-negative, pleomorphic, obligate intracellular bacteria
B. An enveloped, single-stranded, negative sense RNA virus
C. A gram-positive, beta-hemolytic cocci in chains
D. An enveloped, double-stranded DNA virus (Correct Answer)
E. A naked, double-stranded DNA virus
Explanation: ***An enveloped, double-stranded DNA virus***
- This description refers to **Epstein-Barr virus (EBV)**, which is a common cause of **infectious mononucleosis** in children and adolescents.
- Symptoms like **sore throat**, **fever**, **fatigue**, **cervical lymphadenopathy**, and **erythematous tonsils with exudates** are classic for mononucleosis; a negative strep test helps rule out bacterial pharyngitis.
*A gram-negative, pleomorphic, obligate intracellular bacteria*
- This describes organisms like **Chlamydia** or **Rickettsia**, which typically cause different sets of symptoms, such as sexually transmitted infections or tick-borne diseases.
- These are **not common causes of pharyngitis** with exudates and cervical lymphadenopathy in children.
*An enveloped, single-stranded, negative sense RNA virus*
- This describes viruses such as **influenza virus** or **respiratory syncytial virus (RSV)**.
- While these can cause pharyngitis, the overall clinical picture, particularly the prominent **lymphadenopathy** and **exudative tonsillitis** in the presence of a negative strep test, is less typical for these viruses compared to EBV.
*A gram-positive, beta-hemolytic cocci in chains*
- This describes **Group A Streptococcus (GAS)**, which is the causative agent of **streptococcal pharyngitis (strep throat)**.
- Although the symptoms are consistent with strep throat, the information states that the **rapid antigen detection test for streptococcus was negative**, making this diagnosis highly unlikely.
*A naked, double-stranded DNA virus*
- This describes viruses such as **adenoviruses** or **human papillomaviruses**.
- While adenoviruses can cause pharyngitis, the detailed clinical presentation of **prominent exudative tonsillitis** and **cervical lymphadenopathy** in the context of a negative strep test points more strongly to infectious mononucleosis caused by EBV.
Question 79: A 30-year-old man presents with fever, malaise, and severe pain in his right wrist and left knee for the last 2 days. He describes the pain as 8/10 in intensity, sharp in character, and extending from his right wrist to his fingers. He denies any recent inciting trauma or similar symptoms in the past. His past medical history is unremarkable. He is sexually active with multiple partners and uses condoms inconsistently. The vital signs include blood pressure 120/70 mm Hg, pulse 100/min, and temperature 38.3°C (101.0°F). On physical examination, the right wrist and left knee joints are erythematous, warm, and extremely tender to palpation. Both joints have a significantly restricted range of motion. A petechial rash is noted on the right forearm. An arthrocentesis is performed on the left knee joint. Which of the following would be the most likely finding in this patient?
A. Arthrocentesis aspirate showing gram-positive cocci in clusters
B. Positive serum ASO titer
C. Radiographs of right wrist and left knee showing osteopenia and joint space narrowing
D. Arthrocentesis aspirate showing negatively birefringent crystals under polarised light
E. Arthrocentesis aspirate showing abundant, purulent joint effusion with negative culture (Correct Answer)
Explanation: ***Arthrocentesis aspirate showing abundant, purulent joint effusion with negative culture***
- This finding is characteristic of **disseminated gonococcal infection (DGI)**, where joint cultures are often negative due to the fastidious nature of *Neisseria gonorrhoeae*, despite a **purulent** aspirate.
- The patient's presentation with **migratory polyarthralgia**, **tenosynovitis (wrist pain extending to fingers)**, **fever**, **petechial rash**, and **risk factors for STIs** (multiple partners, inconsistent condom use) strongly points towards DGI.
*Arthrocentesis aspirate showing gram-positive cocci in clusters*
- This typically indicates a **staphylococcal septic arthritis**, often *Staphylococcus aureus*, which usually presents as a **monoarticular arthritis** and lacks the migratory polyarthralgia and characteristic rash seen here.
- While septic arthritis can cause purulent effusion, the specific pattern of joint involvement and the patient's risk factors make gonococcal infection more likely.
*Positive serum ASO titer*
- A positive **antistreptolysin O (ASO) titer** is indicative of a recent **Streptococcus pyogenes** infection, often associated with **rheumatic fever**, which can cause migratory polyarthritis.
- However, rheumatic fever typically does not cause a purulent joint effusion, tenosynovitis, or the specific rash described, and the patient's sexual history is not a relevant risk factor for this condition.
*Radiographs of right wrist and left knee showing osteopenia and joint space narrowing*
- **Osteopenia** and **joint space narrowing** are chronic changes seen in long-standing inflammatory or degenerative arthritis (e.g., rheumatoid arthritis, osteoarthritis).
- These findings would not be expected in an acute presentation of only 2 days, where imaging is typically normal or shows only soft tissue swelling.
*Arthrocentesis aspirate showing negatively birefringent crystals under polarised light*
- This finding is pathognomonic for **gout**, caused by **monosodium urate crystals**.
- While gout can present with acute, severe arthritis, it is typically monoarticular (though polyarticular gout can occur), and the patient's risk factors, rash, and tenosynovitis are inconsistent with a primary diagnosis of gout.
Question 80: An 82-year-old woman is brought to the physician by her daughter because of a 3-day history of a runny nose, headache, and cough. The patient's grandson recently had similar symptoms. Her vital signs are within normal limits. Pulse oximetry on room air shows an oxygen saturation of 99%. Lungs are clear to auscultation. Testing of nasal secretions is performed to identify the viral strain. Electron microscopy shows a non-enveloped RNA virus with an icosahedral capsid. Binding to which of the following is responsible for the virulence of this virus?
A. CD21
B. Integrin
C. ICAM-1 (Correct Answer)
D. P antigen
E. Sialic acid residues
Explanation: Both the clinical presentation (runny nose, headache, cough, viral spread) and the electron microscopy finding of a **non-enveloped RNA virus with an icosahedral capsid** are characteristic of a **rhinovirus** (a member of the Picornaviridae family).
***Correct: ICAM-1***
- **Rhinoviruses** primarily infect the upper respiratory tract and bind to **ICAM-1 (intercellular adhesion molecule-1)** on respiratory epithelial cells.
- Approximately **90% of rhinovirus serotypes** use ICAM-1 as their primary cellular receptor.
- This binding facilitates viral entry and is the key factor in the **virulence** of rhinovirus, leading to common cold symptoms.
*Incorrect: CD21*
- **CD21** is the receptor for **Epstein-Barr virus (EBV)**, which causes infectious mononucleosis, a condition distinct from the common cold.
- EBV is an **enveloped DNA virus**, unlike the non-enveloped RNA virus described in this case.
*Incorrect: Integrin*
- **Integrins** are cell adhesion receptors used by some viruses for entry (e.g., certain adenoviruses and enteroviruses).
- However, they are **not the primary receptor** for rhinovirus, which predominantly uses ICAM-1.
- The description of an **icosahedral non-enveloped RNA virus** with upper respiratory symptoms specifically points to rhinovirus and ICAM-1.
*Incorrect: P antigen*
- The **P antigen** (globoside) is the receptor for **parvovirus B19**, which causes Fifth disease (erythema infectiosum) and aplastic crisis.
- Parvovirus B19 is a **non-enveloped DNA virus** (not RNA), which is distinct from the virus described in this question.
*Incorrect: Sialic acid residues*
- **Sialic acid residues** are the receptors for **influenza viruses** (via hemagglutinin) for viral attachment and entry.
- Influenza viruses are **enveloped RNA viruses** and typically cause more severe systemic symptoms (fever, myalgias) than the mild upper respiratory symptoms described here.
