Human herpesvirus 8 (Kaposi sarcoma virus) — MCQs

10 questions

A 76-year-old woman is brought to the physician because of lesions on her left arm. She first noticed them 3 months ago and they have grown larger since that time. She has not had any pain or pruritus in the area. She has a history of invasive ductal carcinoma of the left breast, which was treated with mastectomy and radiation therapy 27 years ago. Since that time, she has had lymphedema of the left arm. Physical examination shows extensive edema of the left arm. There are four coalescing, firm, purple-blue nodules on the left lateral axillary region and swelling of the surrounding skin. Which of the following is the most likely diagnosis?

A scientist is researching the long term effects of the hepatitis viruses on hepatic tissue. She finds that certain strains are oncogenic and increase the risk of hepatocellular carcinoma. However, they appear to do so via different mechanisms. Which of the following answer choices correctly pairs the hepatitis virus with the correct oncogenic process?

Researchers are investigating a new strain of a virus that has been infecting children over the past season and causing dermatitis. They have isolated the virus and have run a number of tests to determine its structure and characteristics. They have found that this new virus has an outer coating that is high in phospholipids. Protein targeting assays and immunofluorescence images have shown that the outer layer contains numerous surface proteins. On microscopy, these surface proteins are also expressed around the nucleus of cells derived from the infected tissue of the children. This virus’s structure most closely resembles which of the following?

A 45-year-old man comes to the emergency department because of chills and numerous skin lesions for 1 week. He has also had watery diarrhea, nausea, and abdominal pain for the past 2 weeks. The skin lesions are nonpruritic and painless. He was diagnosed with HIV infection approximately 20 years ago. He has not taken any medications for over 5 years. He sleeps in homeless shelters and parks. Vital signs are within normal limits. Examination shows several bright red, friable nodules on his face, trunk, extremities. The liver is palpated 3 cm below the right costal margin. His CD4+ T-lymphocyte count is 180/mm3 (N ≥ 500). A rapid plasma reagin test is negative. Abdominal ultrasonography shows hepatomegaly and a single intrahepatic 1.0 x 1.2-cm hypodense lesion. Biopsy of a skin lesion shows vascular proliferation and abundant neutrophils. Which of the following is the most likely causal organism?

An investigator studying patients with symptoms of arthritis detects a nonenveloped virus with a single-stranded DNA genome in the serum of a pregnant patient. Fetal infection with this pathogen is most likely to cause which of the following manifestations?

A 27-year-old woman comes to the physician for a routine health maintenance examination. She feels well. She had a chlamydia infection at the age of 22 years that was treated. Her only medication is an oral contraceptive. She has smoked one pack of cigarettes daily for 6 years. She has recently been sexually active with 3 male partners and uses condoms inconsistently. Her last Pap test was 4 years ago and results were normal. Physical examination shows no abnormalities. A Pap test shows atypical squamous cells of undetermined significance. Which of the following is the most appropriate next step in management?

A pathologist receives a patient sample for analysis. Cells in the sample are first labeled with fluorescent antibodies and then passed across a laser beam in a single file of particles. The light scatter and fluorescent intensity of the particles are plotted on a graph; this information is used to characterize the sample. This laboratory method would be most useful to establish the diagnosis of a patient with which of the following?

A 63-year-old man presents to his primary care physician because he has been having headaches and hearing loss. In addition, he says that he has been having difficulty opening his jaw to eat and recurrent middle ear infections. Physical exam reveals enlarged neck lymph nodes and a mass in the nasopharynx. Biopsy of the mass reveals undifferentiated squamous epithelial cells. The organism that is most likely associated with this patient's disease is also associated with which of the following disorders?

A 24-year-old man presents to the clinic with the complaint of a new rash. The lesions are not bothersome, but he is worried as he has never seen anything like this on his body. Upon further questioning the patient states has been generally healthy except for a one time "horrible" flu-like episode two months ago in June. He has since gotten better. On physical exam the following rash is observed (Figure 1). What is the cause of this patient's rash?

Q10

A previously healthy 5-year-old boy is brought to the physician because of increasing weakness and a retroauricular rash that started 2 days ago. The rash spread rapidly and involves the trunk and extremities. Last week, he had a mild sore throat, pink eyes, and a headache. His family recently immigrated from Ethiopia. His immunization status is unknown. The patient appears severely ill. His temperature is 38.5°C (101.3°F). Examination shows tender postauricular and suboccipital lymphadenopathy. There is a nonconfluent, maculopapular rash over the torso and extremities. Infection with which of the following is the most likely cause of this patient's symptoms?

Human herpesvirus 8 (Kaposi sarcoma virus) US Medical PG Practice Questions and MCQs

Question 1: A 76-year-old woman is brought to the physician because of lesions on her left arm. She first noticed them 3 months ago and they have grown larger since that time. She has not had any pain or pruritus in the area. She has a history of invasive ductal carcinoma of the left breast, which was treated with mastectomy and radiation therapy 27 years ago. Since that time, she has had lymphedema of the left arm. Physical examination shows extensive edema of the left arm. There are four coalescing, firm, purple-blue nodules on the left lateral axillary region and swelling of the surrounding skin. Which of the following is the most likely diagnosis?

A. Thrombophlebitis
B. Cellulitis
C. Melanoma
D. Angiosarcoma (Correct Answer)
E. Kaposi sarcoma

Explanation: ***Angiosarcoma*** - The presence of **firm, purple-blue nodules** in a patient with **chronic lymphedema** following **mastectomy and radiation** for breast cancer is highly suggestive of **angiosarcoma (Stewart-Treves syndrome)**. - This rare but aggressive vascular malignancy often presents as skin lesions in the setting of long-standing lymphedema, particularly in the upper extremity after breast cancer treatment. *Thrombophlebitis* - Typically presents with **erythema**, **tenderness**, and **pain** along the course of a superficial vein, which is not described here. - The lesions would likely blanch with pressure and feel more like a cord or streak, rather than firm, discrete nodules. *Cellulitis* - Would present with **warmth**, **tenderness**, **erythema with ill-defined borders**, and often **fever**, none of which are mentioned. - While lymphedema is a risk factor for cellulitis, the description of discrete, firm, purple-blue nodules growing over time is not characteristic. *Melanoma* - Although melanoma can present as a dark lesion, it often has **irregular borders**, **asymmetry**, and **color variegation**, and is typically associated with UV exposure. - While it can be nodular, the specific context of chronic lymphedema and the description of purple-blue lesions are more indicative of a vascular tumor. *Kaposi sarcoma* - Characterized by **purple-brown skin lesions** and is primarily associated with **HIV infection** or **immunosuppression**, neither of which is indicated in this patient. - While it is a vascular tumor, the unique presentation in the context of chronic lymphedema post-breast cancer therapy makes angiosarcoma a more fitting diagnosis.

Question 2: A scientist is researching the long term effects of the hepatitis viruses on hepatic tissue. She finds that certain strains are oncogenic and increase the risk of hepatocellular carcinoma. However, they appear to do so via different mechanisms. Which of the following answer choices correctly pairs the hepatitis virus with the correct oncogenic process?

A. Hepatitis A virus - chronic inflammation
B. Hepatitis C virus - chronic inflammation
C. Hepatitis E virus - integration of viral DNA into host hepatocyte genome
D. Hepatitis B virus - integration of viral DNA into host hepatocyte genome (Correct Answer)
E. Hepatitis A virus - integration of viral DNA into host hepatocyte genome

Explanation: ***Hepatitis B virus - integration of viral DNA into host hepatocyte genome*** - **Hepatitis B virus (HBV)** is a **DNA virus** that can integrate its genetic material into the host hepatocyte genome, leading to genomic instability and promoting oncogenesis. - This integration, along with chronic inflammation and the production of viral regulatory proteins, contributes significantly to the development of **hepatocellular carcinoma (HCC)**. *Hepatitis A virus - chronic inflammation* - **Hepatitis A virus (HAV)** is an **RNA virus** that causes **acute hepatitis** but does not lead to chronic infection or chronic inflammation. - Due to its acute and self-limiting nature, HAV is **not associated with hepatocellular carcinoma**. *Hepatitis C virus - integration of viral DNA into host hepatocyte genome* - **Hepatitis C virus (HCV)** is an **RNA virus** and therefore does not integrate its DNA into the host genome (as it has no DNA phase). - HCV causes HCC primarily through **chronic inflammation**, **fibrosis**, and **cirrhosis**, not DNA integration. *Hepatitis E virus - integration of viral DNA into host hepatocyte genome* - **Hepatitis E virus (HEV)** is an **RNA virus** that typically causes acute, self-limiting hepatitis and does not integrate its genetic material into the host genome. - While HEV can cause chronic infection in immunocompromised individuals, it is **not generally recognized as an oncogenic virus** leading to HCC. *Hepatitis A virus - integration of viral DNA into host hepatocyte genome* - **Hepatitis A virus (HAV)** is an **RNA virus**, meaning it does not have a DNA stage and therefore cannot integrate DNA into the host genome. - HAV causes **acute, self-limiting infections** and is definitively **not associated with hepatocellular carcinoma**.

Question 3: Researchers are investigating a new strain of a virus that has been infecting children over the past season and causing dermatitis. They have isolated the virus and have run a number of tests to determine its structure and characteristics. They have found that this new virus has an outer coating that is high in phospholipids. Protein targeting assays and immunofluorescence images have shown that the outer layer contains numerous surface proteins. On microscopy, these surface proteins are also expressed around the nucleus of cells derived from the infected tissue of the children. This virus’s structure most closely resembles which of the following?

A. Adenovirus
B. Papillomavirus
C. Herpesvirus (Correct Answer)
D. Poxvirus
E. Hepadnavirus

Explanation: ***Herpesvirus*** - The presence of an **outer coating high in phospholipids** indicates an **enveloped virus**. Herpesviruses are large, enveloped DNA viruses. - The detection of surface proteins expressed around the **nucleus** is a key finding that suggests the virus **buds from the nuclear membrane**, a characteristic feature of **herpesviruses**. - Many herpesviruses cause dermatitis, including **HSV-1, HSV-2, VZV**, and **HHV-6**. *Adenovirus* - Adenoviruses are **non-enveloped viruses**, meaning they lack a lipid outer coating, which contradicts the phospholipid-rich coating described. - Their replication and assembly occur exclusively in the **nucleus**, but they do not acquire an envelope by budding from the nuclear membrane. *Papillomavirus* - Papillomaviruses are also **non-enveloped viruses** with an **icosahedral capsid**, lacking the phospholipid envelope described. - They replicate and assemble in the nucleus but do not possess the phospholipid-rich outer coating. *Poxvirus* - While poxviruses are **enveloped**, they acquire their envelope from the **Golgi apparatus** or **plasma membrane**, not the nuclear membrane. - They are also distinct from other DNA viruses in that they replicate entirely in the **cytoplasm**, not the nucleus, which does not explain the perinuclear protein expression. *Hepadnavirus* - Hepadnaviruses (e.g., **Hepatitis B virus**) are enveloped DNA viruses, but their envelope is acquired by budding through the **endoplasmic reticulum** and **Golgi apparatus**, not the nuclear membrane. - The perinuclear localization of surface proteins in immunofluorescence is not a characteristic feature of hepadnaviruses.

Question 4: A 45-year-old man comes to the emergency department because of chills and numerous skin lesions for 1 week. He has also had watery diarrhea, nausea, and abdominal pain for the past 2 weeks. The skin lesions are nonpruritic and painless. He was diagnosed with HIV infection approximately 20 years ago. He has not taken any medications for over 5 years. He sleeps in homeless shelters and parks. Vital signs are within normal limits. Examination shows several bright red, friable nodules on his face, trunk, extremities. The liver is palpated 3 cm below the right costal margin. His CD4+ T-lymphocyte count is 180/mm3 (N ≥ 500). A rapid plasma reagin test is negative. Abdominal ultrasonography shows hepatomegaly and a single intrahepatic 1.0 x 1.2-cm hypodense lesion. Biopsy of a skin lesion shows vascular proliferation and abundant neutrophils. Which of the following is the most likely causal organism?

A. Bartonella henselae (Correct Answer)
B. Treponema pallidum
C. HHV-8 virus
D. Mycobacterium avium
E. Candida albicans

Explanation: ***Bartonella henselae*** - The patient's presentation with **bright red, friable nodules** (consistent with **bacillary angiomatosis**) in an HIV-positive individual with a low **CD4+ count** strongly suggests infection with *Bartonella henselae*. - **Hepatomegaly** and **intrahepatic lesions** further support disseminated bartonellosis, and skin biopsy showing vascular proliferation with **abundant neutrophils** is characteristic. *Treponema pallidum* - While *Treponema pallidum* (syphilis) can cause various skin lesions, the **rapid plasma reagin (RPR) test** was negative, making syphilis highly unlikely. - Syphilitic lesions typically do not present as brightly friable nodules with prominent vascular proliferation and neutrophils characteristic of bacillary angiomatosis. *HHV-8 virus* - **HHV-8** is the causative agent of **Kaposi sarcoma**, which also presents with vascular lesions. However, Kaposi sarcoma lesions are typically **violaceous plaques or nodules** and histologically show spindle cells and extravasated red blood cells, not the prominent neutrophils seen here. - The patient's clinical presentation, particularly the friable nature and specific histology, steers away from Kaposi sarcoma. *Mycobacterium avium* - *Mycobacterium avium* complex (MAC) can cause disseminated disease in HIV patients with low CD4 counts, often presenting with fever, weight loss, and gastrointestinal symptoms. - However, MAC infection rarely causes specific nonpruritic, bright red, friable skin nodules like those described, and hepatic lesions would typically be granulomatous, not necessarily angiomatous. *Candida albicans* - While *Candida albicans* can cause various infections in immunocompromised individuals, including esophagitis and mucocutaneous candidiasis, it does not typically present with these specific bright red, friable vascular skin nodules. - Disseminated candidiasis would more likely involve fungemia and widespread organ involvement, often with more subtle or different skin manifestations (e.g., maculopapular rash).

Question 5: An investigator studying patients with symptoms of arthritis detects a nonenveloped virus with a single-stranded DNA genome in the serum of a pregnant patient. Fetal infection with this pathogen is most likely to cause which of the following manifestations?

A. Hydrops fetalis (Correct Answer)
B. Notched teeth
C. Microcephaly
D. Chorioretinitis
E. Vesicular rash

Explanation: ***Hydrops fetalis*** - The description of a nonenveloped virus with a **single-stranded DNA genome** is characteristic of **Parvovirus B19**. This virus commonly causes hydrops fetalis due to **fetal anemia** and subsequent heart failure. - Parvovirus B19 infection in pregnant women can lead to severe complications for the fetus, primarily due to tropism for **erythroid progenitor cells**, resulting in anemia. *Notched teeth* - **Hutchinson's teeth**, characterized by notches, are a classic manifestation of **congenital syphilis**, caused by the bacterium *Treponema pallidum*, not a virus. - Syphilis is a spirochete and not a single-stranded DNA virus. *Microcephaly* - **Microcephaly** is a severe neurological abnormality often associated with congenital infections like **Zika virus** or **cytomegalovirus (CMV)**, which are RNA and double-stranded DNA viruses, respectively. - While viral infections can cause microcephaly, Parvovirus B19 is primarily known for causing fetal anemia and hydrops, not typically microcephaly. *Chorioretinitis* - **Chorioretinitis** is a common ocular manifestation of congenital infections such as **toxoplasmosis**, **CMV**, and **rubella**, but it is not a hallmark of Parvovirus B19 infection. - These pathogens have different genomic structures and disease presentations. *Vesicular rash* - A **vesicular rash** is characteristic of infections caused by **herpesviruses**, such as **varicella-zoster virus (VZV)** or herpes simplex virus. - These are **double-stranded DNA viruses**, not single-stranded DNA viruses like Parvovirus B19.

Question 6: A 27-year-old woman comes to the physician for a routine health maintenance examination. She feels well. She had a chlamydia infection at the age of 22 years that was treated. Her only medication is an oral contraceptive. She has smoked one pack of cigarettes daily for 6 years. She has recently been sexually active with 3 male partners and uses condoms inconsistently. Her last Pap test was 4 years ago and results were normal. Physical examination shows no abnormalities. A Pap test shows atypical squamous cells of undetermined significance. Which of the following is the most appropriate next step in management?

A. Repeat cytology in 6 months
B. Perform laser ablation
C. Perform loop electrosurgical excision procedure
D. Perform HPV testing (Correct Answer)
E. Perform cervical biopsy

Explanation: ***Perform HPV testing*** - For women aged 25-29 with **Atypical Squamous Cells of Undetermined Significance (ASC-US)**, **HPV co-testing** is the preferred next step to risk-stratify for high-grade lesions. - If **HPV is positive**, the patient should proceed to **colposcopy**; if HPV is negative, she can return to routine screening. *Repeat cytology in 6 months* - This approach is typically recommended for adolescents (age <21) with ASC-US or for women aged 21-24 where HPV testing is often not performed due to the high rate of transient HPV infections. - For women aged ≥25 years with ASC-US, **reflex HPV testing** or **HPV co-testing** (if not done with the initial Pap) is generally preferred over repeat cytology alone. *Perform laser ablation* - **Laser ablation** is a treatment for **high-grade cervical intraepithelial neoplasia (CIN2/3)** identified after colposcopy and biopsy, not for initial ASC-US findings. - Initiating a destructive procedure without further diagnostic evaluation would be premature and over-treatment for ASC-US. *Perform loop electrosurgical excision procedure* - **LEEP (loop electrosurgical excision procedure)** is a **diagnostic and therapeutic procedure** typically reserved for confirmed **high-grade CIN (CIN2 or CIN3)** or adenocarcinoma in situ. - It is an invasive procedure and not appropriate as the initial management step for an ASC-US Pap result. *Perform cervical biopsy* - A **cervical biopsy** is performed during a **colposcopy** if abnormal areas are identified, usually following a positive HPV test or higher-grade abnormal cytology (e.g., LSIL, HSIL). - ASC-US alone does not automatically warrant an immediate colposcopy and biopsy without prior **HPV risk stratification**.

Question 7: A pathologist receives a patient sample for analysis. Cells in the sample are first labeled with fluorescent antibodies and then passed across a laser beam in a single file of particles. The light scatter and fluorescent intensity of the particles are plotted on a graph; this information is used to characterize the sample. This laboratory method would be most useful to establish the diagnosis of a patient with which of the following?

A. Ventricular septal defect and facial dysmorphism with low T-lymphocyte count
B. Painless generalized lymphadenopathy with monomorphic cells and interspersed benign histiocytes on histology
C. Pancytopenia and deep vein thrombosis with intermittent hemoglobinuria (Correct Answer)
D. Multiple opportunistic infections with decreased CD4 counts
E. Vesicular lesions with dermatomal distribution and dendritic corneal ulcers

Explanation: ***Pancytopenia and deep vein thrombosis with intermittent hemoglobinuria*** - The described laboratory method is **flow cytometry**, which is the **gold standard for diagnosing paroxysmal nocturnal hemoglobinuria (PNH)** by detecting the absence of **CD55** and **CD59** on red blood cells due to impaired GPI anchor synthesis. - PNH classically presents with **pancytopenia**, **hemolytic anemia** (leading to hemoglobinuria), and a high risk of **thrombosis** (e.g., deep vein thrombosis). *Ventricular septal defect and facial dysmorphism with low T-lymphocyte count* - This clinical picture suggests **DiGeorge syndrome**, which involves a developmental defect of the **third and fourth pharyngeal pouches**, leading to thymic hypoplasia and **T-cell deficiency**. - While flow cytometry is used to quantify T-lymphocyte subsets (e.g., CD3, CD4, CD8), the primary method for diagnosing DiGeorge syndrome is **fluorescent in situ hybridization (FISH)** for a **22q11 deletion**, making it less ideal for flow cytometry diagnosis. *Painless generalized lymphadenopathy with monomorphic cells and interspersed benign histiocytes on histology* - This description with "**monomorphic cells**" is more consistent with certain **non-Hodgkin lymphomas** (e.g., Burkitt lymphoma) rather than Hodgkin lymphoma, which typically shows a **polymorphic** cellular infiltrate. - While flow cytometry can be useful in characterizing lymphomas by identifying cell surface markers, the diagnosis is primarily established by **lymph node biopsy and histopathology** with **immunohistochemistry**, making flow cytometry a supplementary rather than primary diagnostic tool. *Multiple opportunistic infections with decreased CD4 counts* - This presentation is highly suggestive of **HIV infection leading to AIDS**. The "decreased CD4 counts" are a key diagnostic and prognostic marker. - While flow cytometry is used to **monitor CD4 cell counts** in HIV patients, the initial diagnosis of HIV is established via **antibody/antigen combination tests** and confirmed by **Western blot** or **PCR for viral load**, not by flow cytometry. *Vesicular lesions with dermatomal distribution and dendritic corneal ulcers* - This clinical presentation points to **herpes zoster ophthalmicus** (shingles affecting the eye due to **varicella-zoster virus** reactivation). - Diagnosis is primarily **clinical** based on the characteristic rash and eye findings, although **PCR** of vesicular fluid can confirm VZV infection. Flow cytometry has no role in this diagnosis.

Question 8: A 63-year-old man presents to his primary care physician because he has been having headaches and hearing loss. In addition, he says that he has been having difficulty opening his jaw to eat and recurrent middle ear infections. Physical exam reveals enlarged neck lymph nodes and a mass in the nasopharynx. Biopsy of the mass reveals undifferentiated squamous epithelial cells. The organism that is most likely associated with this patient's disease is also associated with which of the following disorders?

A. Kaposi sarcoma
B. Hepatocellular carcinoma
C. Adult T-cell lymphoma
D. Burkitt lymphoma (Correct Answer)
E. Vulvar carcinoma

Explanation: ***Burkitt lymphoma*** - The patient's symptoms (headaches, hearing loss, difficulty opening jaw, recurrent middle ear infections, nasopharyngeal mass, enlarged neck lymph nodes) and biopsy results (undifferentiated squamous epithelial cells) point to **nasopharyngeal carcinoma**. - **Nasopharyngeal carcinoma** is strongly associated with the **Epstein-Barr virus (EBV)**. EBV is also a causative agent in **Burkitt lymphoma**. *Kaposi sarcoma* - **Kaposi sarcoma** is caused by **Human Herpesvirus 8 (HHV-8)**, not EBV. - It typically presents as vascular skin lesions and can affect visceral organs, differing from the nasopharyngeal carcinoma described. *Hepatocellular carcinoma* - **Hepatocellular carcinoma** is primarily associated with **Hepatitis B virus (HBV)** and **Hepatitis C virus (HCV)** infection, as well as cirrhosis from other causes. - There is no significant association between EBV and hepatocellular carcinoma. *Adult T-cell lymphoma* - **Adult T-cell lymphoma** is caused by the **Human T-lymphotropic virus type 1 (HTLV-1)**. - This is a retrovirus distinct from EBV. *Vulvar carcinoma* - **Vulvar carcinoma** is most frequently associated with **Human Papillomavirus (HPV)** infection, especially high-risk strains like HPV 16 and 18. - It is not typically linked to EBV.

Question 9: A 24-year-old man presents to the clinic with the complaint of a new rash. The lesions are not bothersome, but he is worried as he has never seen anything like this on his body. Upon further questioning the patient states has been generally healthy except for a one time "horrible" flu-like episode two months ago in June. He has since gotten better. On physical exam the following rash is observed (Figure 1). What is the cause of this patient's rash?

A. Molluscum contagiosum virus (Correct Answer)
B. Varicella zoster virus (VZV)
C. Human immunodeficiency virus (HIV)
D. Human papilloma virus (HPV)
E. Staphylococcus aureus cellulitis

Explanation: ***Molluscum contagiosum virus*** - The image displays characteristic **umbilicated papules**, which are pathognomonic for **molluscum contagiosum**, a viral skin infection. - The history of a "horrible" flu-like episode two months prior could suggest recent **immunocompromise** or an acute retroviral syndrome, making the patient more susceptible to or exacerbating molluscum contagiosum. *Varicella zoster virus (VZV)* - VZV typically causes **vesicles on an erythematous base** that evolve into **crusted lesions** in a dermatomal distribution (shingles) or widespread (chickenpox), which is not consistent with the described rash. - While VZV can reactivate due to immunocompromise, the morphology of the rash does not fit a typical VZV presentation like chickenpox or shingles. *Human immunodeficiency virus (HIV)* - While **HIV infection** can lead to various skin manifestations, including increased susceptibility to molluscum contagiosum, it is not the direct cause of the rash itself. - The flu-like episode could represent acute retroviral syndrome, but HIV itself does not cause this specific papular rash, rather it creates an environment for opportunistic infections or conditions like molluscum. *Human papilloma virus (HPV)* - HPV causes **warts** (verrucae) which are typically **rough, hyperkeratotic papules** or lesions with a cauliflower-like appearance, a different morphology than seen in the image. - While HPV infections are common, the characteristic smooth, umbilicated papules seen here are not consistent with typical HPV-induced lesions. *Staphylococcus aureus cellulitis* - **Cellulitis** is a **bacterial skin infection** characterized by localized areas of **redness, warmth, swelling, and pain**, often with poorly defined borders, which are absent in this presentation. - **Staphylococcus aureus** can cause various skin infections, but not the distinct umbilicated papules observed in the image; these lesions are viral, not bacterial.

Question 10: A previously healthy 5-year-old boy is brought to the physician because of increasing weakness and a retroauricular rash that started 2 days ago. The rash spread rapidly and involves the trunk and extremities. Last week, he had a mild sore throat, pink eyes, and a headache. His family recently immigrated from Ethiopia. His immunization status is unknown. The patient appears severely ill. His temperature is 38.5°C (101.3°F). Examination shows tender postauricular and suboccipital lymphadenopathy. There is a nonconfluent, maculopapular rash over the torso and extremities. Infection with which of the following is the most likely cause of this patient's symptoms?

A. Togavirus (Correct Answer)
B. Human herpesvirus 6
C. Parvovirus
D. Varicella zoster virus
E. Paramyxovirus

Explanation: ***Togavirus*** - This patient's presentation is classic for **rubella** (German measles), caused by the **rubella virus**, a **togavirus**. - The hallmark clinical finding is **tender postauricular and suboccipital lymphadenopathy**, which appears before the rash and is pathognomonic for rubella. - The **maculopapular rash** begins on the face (retroauricular region) and spreads cephalocaudally to the trunk and extremities over 2-3 days. - The prodrome includes **mild symptoms** (low-grade fever, sore throat, mild conjunctivitis, headache), which is characteristic of rubella. - The patient's **unknown immunization status** and immigration from a region with lower vaccination coverage increases the likelihood of rubella infection. *Paramyxovirus* - **Measles virus** is a paramyxovirus that causes rubeola, but the clinical presentation differs significantly from this case. - Measles typically presents with the **"3 Cs"**: severe **cough**, **coryza** (profuse nasal discharge), and **conjunctivitis** (more prominent than rubella). - **Koplik spots** (white spots on buccal mucosa) are pathognomonic for measles and appear before the rash. - Measles causes **higher fever** (often >40°C) and more severe systemic illness than described here. - While measles can have lymphadenopathy, the **prominent postauricular and suboccipital nodes are characteristic of rubella, not measles**. *Human herpesvirus 6* - **HHV-6** causes **roseola infantum** (exanthem subitum), typically in infants 6-24 months old. - The classic presentation is **high fever for 3-5 days** that suddenly resolves, followed immediately by a rash (**"fever then rash"**). - This patient had prodromal symptoms followed by rash while still febrile, which does not fit roseola. - Roseola does not cause significant lymphadenopathy or conjunctivitis. *Parvovirus* - **Parvovirus B19** causes **erythema infectiosum** (fifth disease), characterized by a **"slapped cheek"** facial erythema followed by a reticular (lacy) rash on the trunk and extremities. - The rash pattern and prominent lymphadenopathy in this case are not consistent with fifth disease. - Fifth disease typically causes mild or no fever and lacks the retroauricular distribution seen here. *Varicella zoster virus* - **VZV** causes **chickenpox**, which presents with a **pruritic, vesicular rash** that appears in successive crops and progresses through stages (macule → papule → vesicle → crust). - This patient has a **maculopapular, nonconfluent rash** without vesicles, which is inconsistent with chickenpox. - Chickenpox does not typically cause prominent postauricular lymphadenopathy.

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