Question 131: A 48-year-old man with HIV comes to the physician because of skin lesions over his face and neck for 2 weeks. They are not itchy or painful. He does not have fever or a sore throat. He was treated for candidal esophagitis 3 months ago. He is sexually active with his wife, who knows of his condition, and uses condoms consistently. He is currently receiving triple antiretroviral therapy with lamivudine, abacavir, and efavirenz. He is 175 cm (5 ft 9 in) tall and weighs 58 kg (128 lb); BMI is 18.8 kg/m2. Examination shows multiple skin colored papules over his face and neck with a dimpled center. Cervical lymphadenopathy is present. The remainder of the examination is unremarkable. His hemoglobin concentration is 12.1 g/dL, leukocyte count is 4,900/mm3, and platelet count is 143,000/mm3; serum studies and urinalysis show no abnormalities. CD4+ T-lymphocyte count is 312/mm3 (normal ≥ 500). Which of the following is the most likely cause of this patient's findings?
- A. Poxvirus (Correct Answer)
- B. A herpesvirus
- C. Papillomavirus
- D. Coccidioides
- E. Bartonella
Explanation: ***Poxvirus***
- The description of **skin-colored papules with a dimpled (umbilicated) center** is highly characteristic of **molluscum contagiosum**, which is caused by a poxvirus. This condition is common in immunocompromised individuals, such as those with HIV.
- The patient's **HIV-positive status** and **CD4+ count of 312/mm³** indicate immunocompromise, making him susceptible to severe or widespread molluscum contagiosum, often seen on the face and neck.
*A herpesvirus*
- Herpes simplex virus typically causes **painful, clustered vesicles** on an erythematous base, often with recurrent outbreaks; this presentation does not match the described painless, umbilicated papules.
- Varicella-zoster virus (another herpesvirus) causes chickenpox or shingles, presenting as **vesicles and crusts in a dermatomal pattern** (shingles) or diffuse rash (chickenpox), which is inconsistent with this patient's lesions.
*Papillomavirus*
- Human papillomavirus (HPV) causes **warts**, which are typically rough, hyperkeratotic papules or nodules, lacking the characteristic central umbilication seen in this patient.
- While common in immunocompromised individuals, HPV lesions usually present differently and are not described as skin-colored with a dimpled center.
*Coccidioides*
- **Coccidioidomycosis** is a fungal infection that can cause various skin manifestations, including **erythema nodosum**, **erythema multiforme**, or subcutaneous nodules, but not the distinct umbilicated papules characteristic of molluscum contagiosum.
- Systemic symptoms like fever, cough, and fatigue are common in disseminated coccidioidomycosis, and while skin lesions can occur, they do not typically present as solitary or multiple umbilicated papules.
*Bartonella*
- *Bartonella* infections, particularly *Bartonella henselae* (cat scratch disease) or *Bartonella quintana* (bacillary angiomatosis), typically present as **reddish-purple vascular lesions** (angiomatous papules or nodules) or localized lymphadenopathy.
- The lesions described are skin-colored and umbilicated, not vascular, making *Bartonella* an unlikely cause.
Question 132: A 12-year-old boy who recently emigrated from Pakistan presents with fever, muscle pain, and weakness of the trunk, abdomen, and legs. The patient’s mother says that he has not been vaccinated. Physical examination reveals fasciculation and flaccid paralysis of the lower limbs. A CSF analysis reveals lymphocytosis with normal glucose and protein levels. A throat swab reveals an RNA virus. Which of the following would most likely be destroyed by the virus in this patient?
- A. Anterior horn of the spinal cord (Correct Answer)
- B. Basal ganglia
- C. Posterior horn cells of the spinal cord
- D. Myelin sheath of neurons
- E. Muscle cells
Explanation: ***Anterior horn of the spinal cord***
- The symptoms of **flaccid paralysis** and **fasciculation** in a non-vaccinated child from an endemic area (Pakistan) are classic for **poliomyelitis**, caused by the **poliovirus**.
- Poliovirus specifically targets and destroys the neuronal cell bodies located in the **anterior horn of the spinal cord**, leading to lower motor neuron lesions.
*Basal ganglia*
- The **basal ganglia** are involved in movement control, but their damage typically results in **movement disorders** like Parkinsonism or chorea, not flaccid paralysis.
- Poliovirus does not primarily target the basal ganglia.
*Posterior horn cells of the spinal cord*
- The **posterior horn cells** are primarily involved in **sensory processing** and are not the target of the poliovirus.
- Damage to these cells would cause sensory deficits rather than motor weakness and paralysis.
*Myelin sheath of neurons*
- Destruction of the **myelin sheath** (demyelination) is characteristic of diseases like **multiple sclerosis** or Guillain-Barré syndrome, leading to conduction abnormalities.
- Poliovirus does not directly attack the myelin sheath.
*Muscle cells*
- While muscle weakness is a symptom, **poliovirus** directly damages the **motor neurons** that innervate the muscles, not the muscle cells themselves initially.
- The muscle pathology observed in polio is secondary to the denervation caused by anterior horn cell destruction.
