Infections of the Nervous System — MCQs

10 questions

A 29-year-old patient presents with focal seizures. MRI shows frontal and temporal enhancement. What is the most probable diagnosis?

A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?

The typical CSF profile in cases of viral meningitis after 48 hours of onset is -

In bacterial meningitis, CSF has:

What is the primary pathological mechanism in classical Guillain-Barré syndrome affecting the peripheral nervous system?

A child presented with microcephaly, hepatomegaly and periventricular calcification. What is the best specimen for diagnosis of CMV by PCR?

All of the following statements are true regarding central nervous system infections, except:

A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

In severe CNS infections in children with complications, treatment may include:

Q10

Which of the following is the MOST accurate statement about CSF?

Infections of the Nervous System Indian Medical PG Practice Questions and MCQs

Question 1: A 29-year-old patient presents with focal seizures. MRI shows frontal and temporal enhancement. What is the most probable diagnosis?

A. Herpes simplex encephalitis (Correct Answer)
B. Enterovirus encephalitis
C. Japanese encephalitis
D. Meningococcal meningitis

Explanation: ***Herpes simplex encephalitis*** - **Herpes simplex encephalitis (HSE)** characteristically causes inflammation and damage in the **frontal** and **temporal lobes**, leading to focal neurological deficits and seizures [1]. - MRI findings of **enhancement** in these specific brain regions are highly suggestive of HSE. *Enterovirus encephalitis* - **Enterovirus encephalitis** typically affects a broader range of brain regions and less commonly presents with the focal frontal and temporal enhancement seen in HSE. - While it can cause seizures, the MRI findings are not as specific for this diagnosis. *Japanese encephalitis* - **Japanese encephalitis** is geographically restricted to parts of Asia and is transmitted by mosquitoes. The clinical presentation typically includes diffuse encephalitic symptoms rather than focal frontal/temporal involvement and enhancement on MRI. - This diagnosis would be unlikely without a relevant travel history and exposure. *Meningococcal meningitis* - **Meningococcal meningitis** is an infection of the **meninges**, the membranes surrounding the brain and spinal cord, not primarily the brain tissue itself. - MRI would typically show inflammation and enhancement of the meninges, rather than focal parenchymal (brain tissue) enhancement in the frontal and temporal lobes.

Question 2: A patient with AIDS presents with meningitis. India ink staining shows encapsulated yeasts. Which organism is most likely?

A. Candida albicans
B. Cryptococcus neoformans (Correct Answer)
C. Histoplasma capsulatum
D. Coccidioides immitis

Explanation: ***Cryptococcus neoformans*** - This fungus is a common cause of **meningitis in AIDS patients** and characteristically appears as **encapsulated yeasts** on India ink staining of CSF. - The capsule excludes the ink, creating a distinct **halo** around the yeast cell, which is diagnostic. *Candida albicans* - While *Candida* can cause systemic infections, including meningitis, it typically presents as **pseudohyphae** or budding yeast without an obvious capsule on India ink stain. - *Candida meningitis* is less common in AIDS patients compared to *Cryptococcus*. *Histoplasma capsulatum* - This is a dimorphic fungus that causes **histoplasmosis**, often disseminated in AIDS patients, but typically manifests as **pulmonary disease** or hepatosplenomegaly. - It appears as small, **intracellular yeasts** within macrophages and would not show an encapsulated form on India ink stain in CSF. *Coccidioides immitis* - This dimorphic fungus causes **coccidioidomycosis**, which can lead to meningitis, particularly in immunocompromised individuals. - In CSF, it is seen as **spherules containing endospores**, not encapsulated yeasts, which is a distinct morphological feature.

Question 3: The typical CSF profile in cases of viral meningitis after 48 hours of onset is -

A. Neutrophilic pleocytosis, raised glucose level, normal protein level
B. Lymphocytic pleocytosis, low glucose level, low protein level
C. Lymphocytic pleocytosis, normal glucose level, normal or slightly elevated protein level (Correct Answer)
D. Neutrophilic pleocytosis, normal glucose level, elevated protein level

Explanation: ***Lymphocytic pleocytosis, normal glucose level, normal or slightly elevated protein level*** - After 48 hours, the **CSF analysis** in viral meningitis typically shows a predominance of **lymphocytes** (lymphocytic pleocytosis) as the immune response shifts from neutrophils to mononuclear cells [1]. - Glucose levels remain **normal** in viral meningitis because viruses do not consume glucose, and protein levels are usually **normal to slightly elevated** due to mild inflammation and increased blood-brain barrier permeability [1]. *Neutrophilic pleocytosis, raised glucose level, normal protein level* - **Neutrophilic pleocytosis** is characteristic of **bacterial meningitis**, especially in the initial stages, not viral meningitis. - **Raised glucose levels** in CSF are not a feature of meningitis; glucose levels are typically normal or low in infectious meningitis. *Lymphocytic pleocytosis, low glucose level, low protein level* - While **lymphocytic pleocytosis** is seen in viral meningitis, a **low glucose level** (**hypoglycorrhachia**) is more commonly associated with **bacterial** or **fungal meningitis**, as these pathogens consume glucose. - A **low protein level** is also atypical for meningitis, where protein levels are generally normal or elevated. *Neutrophilic pleocytosis, normal glucose level, elevated protein level* - **Neutrophilic pleocytosis** is characteristic of **bacterial meningitis**, not viral meningitis, particularly after 48 hours. - Although **elevated protein levels** can be seen in both viral and bacterial meningitis, the presence of **neutrophilic pleocytosis** makes this option less likely for viral meningitis.

Question 4: In bacterial meningitis, CSF has:

A. High glucose
B. High neutrophils
C. High lymphocytes
D. High protein (Correct Answer)

Explanation: High protein - In bacterial meningitis, inflammation and increased permeability of the blood-brain barrier lead to significant leakage of plasma proteins into the cerebrospinal fluid (CSF), resulting in elevated CSF protein levels [1]. - This is a hallmark finding due to the breakdown of normal barrier function and the presence of bacterial exudates [1]. *High glucose* - Bacterial meningitis is characterized by low CSF glucose because bacteria metabolize glucose for their growth and survival. - White blood cells also consume glucose, further decreasing its concentration in the CSF. *High lymphocytes* - While lymphocytes may be present, the predominant cell type in acute bacterial meningitis is neutrophils, indicating an acute inflammatory response [1]. - Lymphocyte predominance is typically seen in viral or chronic meningitis [2]. *High neutrophils* - High neutrophils are indeed characteristic of bacterial meningitis, reflecting the acute inflammatory response to bacterial pathogens [1]. - However, the question asks for a single characteristic, and while neutrophilic pleocytosis is prominent, elevated protein is another consistent and significant finding.

Question 5: What is the primary pathological mechanism in classical Guillain-Barré syndrome affecting the peripheral nervous system?

A. It blocks neurotransmitter release.
B. It causes demyelination of peripheral nerves. (Correct Answer)
C. It inhibits muscle contraction.
D. It leads to axonal degeneration.

Explanation: ***It causes demyelination of peripheral nerves.*** - Classical Guillain-Barré syndrome (AIDP - Acute Inflammatory Demyelinating Polyneuropathy) is an autoimmune disorder where the immune system attacks the **myelin sheath** surrounding peripheral nerves. - This **demyelination** impairs nerve signal conduction, leading to weakness and paralysis. - AIDP represents the most common form of GBS in Western countries (~85-90% of cases). *It blocks neurotransmitter release.* - Conditions like **Lambert-Eaton myasthenic syndrome** primarily involve antibodies targeting presynaptic voltage-gated calcium channels, thereby reducing neurotransmitter release. - While GBS affects nerve conduction, its primary mechanism is not the blockage of neurotransmitter release at the synapse. *It inhibits muscle contraction.* - Inhibition of muscle contraction is a downstream effect of impaired nerve innervation, but the fundamental problem in GBS is with the **nerve itself**, not the muscle's ability to contract directly. - Conditions like **myasthenia gravis** directly affect neuromuscular transmission by blocking acetylcholine receptors on muscle fibers. *It leads to axonal degeneration.* - While **axonal variants** of GBS exist (AMAN - Acute Motor Axonal Neuropathy; AMSAN - Acute Motor-Sensory Axonal Neuropathy), particularly common in Asia, the **classical and most common form** is characterized by **primary demyelination** (AIDP). - Pure axonal degeneration as a primary pathology is seen in specific GBS variants, not the classical presentation. - Secondary axonal damage can occur in severe or prolonged cases.

Question 6: A child presented with microcephaly, hepatomegaly and periventricular calcification. What is the best specimen for diagnosis of CMV by PCR?

A. CSF
B. Blood
C. Liver biopsy
D. Urine (Correct Answer)

Explanation: ***Urine*** - **Urine** is the most sensitive and commonly used specimen for diagnosing **congenital CMV infection** via PCR, especially in neonates, due to high viral shedding in urine. - A positive urine CMV PCR within the first 2-3 weeks of life is highly indicative of **congenital CMV**, which can cause symptoms like **microcephaly**, **hepatomegaly**, and **periventricular calcifications**. *CSF* - While CMV can be detected in **CSF** in congenital infections, particularly in symptomatic cases with neurological involvement, it is less sensitive than urine for initial diagnosis. - **CSF PCR** is typically reserved for evaluating central nervous system involvement and may not detect systemic infection as reliably as urine. *Blood* - **Blood PCR** for CMV can be positive in congenital infection, but it can also be positive in postnatal CMV acquisition or maternal viremia without congenital transmission. - The presence of viral DNA in blood is transient, and its sensitivity for diagnosing congenital infection is generally lower than that of urine. *Liver biopsy* - **Liver biopsy** is an invasive procedure and is not the primary diagnostic method for CMV infection, although histological examination can reveal characteristic viral inclusions if there is significant hepatic involvement. - It carries risks and is typically performed only when other diagnostic methods are inconclusive or when assessing the extent of liver damage.

Question 7: All of the following statements are true regarding central nervous system infections, except:

A. Prions infection causes spongiform encephalopathy
B. JC virus is causative agent for progressive multifocal leucoencephalopathy
C. Cytomegalovirus is a common cause of bilateral temporal lobe hemorrhagic infarction (Correct Answer)
D. Measles virus is the causative agent for subacute sclerosing pan encephalitis (SSPE)

Explanation: ***Cytomegalovirus is a common cause of bilateral temporal lobe hemorrhagic infarction.*** - **Cytomegalovirus (CMV)** typically causes **ventriculoencephalitis or periventricular necrosis** and microglial nodules in immunocompromised patients, not bilateral temporal lobe hemorrhagic infarction. - **Herpes simplex virus type 1 (HSV-1)** is the classic infectious cause of **bilateral temporal lobe hemorrhagic infarction (necrotizing encephalitis)**. *Prions infection causes spongiform encephalopathy* - **Prions** are misfolded proteins that cause transmissible spongiform encephalopathies (TSEs), such as Creutzfeldt-Jakob disease, characterized by **neuronal loss** and vacuolation (spongiform changes). - These diseases are invariably fatal and lead to rapid neurological deterioration. *JC virus is causative agent for progressive multifocal leucoencephalopathy* - The **JC virus** specifically targets and destroys **oligodendrocytes**, the myelin-producing cells of the central nervous system. - This leads to **demyelination** in multiple areas of the brain, causing the characteristic lesions seen in progressive multifocal leukoencephalopathy (PML). *Measles virus is the causative agent for subacute sclerosing pan encephalitis (SSPE).* - **Subacute sclerosing panencephalitis (SSPE)** is a rare, fatal, progressive neurodegenerative disease caused by a persistent and defective **measles virus infection** in the brain. - It occurs years after the initial measles infection, leading to cognitive decline, seizures, and motor dysfunction.

Question 8: A 47-year-old man with chronic asthma who has been treated with steroids for many years develops a productive cough, weight loss, and night sweats. Imaging studies reveal the presence of abscesses in the lungs and brain. Cultures show gram-positive filaments that are weakly acid-fast. Which of the following organisms is responsible for this patient's condition?

A. Actinomyces israelii
B. Nocardia asteroides (Correct Answer)
C. Bacillus anthracis
D. Mycobacterium tuberculosis

Explanation: ***Nocardia asteroides*** - The presence of **productive cough, weight loss, night sweats**, and **abscesses in the lungs and brain** in an immunocompromised patient (due to chronic steroid use for asthma) is highly suggestive of Nocardiosis. - Identification of **gram-positive, branching filaments** that are **weakly acid-fast** in cultures confirms *Nocardia* as the causative organism. *Actinomyces israelii* - While *Actinomyces* causes chronic abscesses and is a **gram-positive filamentous bacterium**, it is **not acid-fast** and typically causes cervicofacial, thoracic, or abdominal infections often associated with trauma or surgery, not disseminated brain abscesses in this context. - *Actinomyces* infections are characterized by **"sulfur granules"** in pus, which are not mentioned here. *Bacillus anthracis* - *Bacillus anthracis* is a **gram-positive rod** that causes **anthrax**, typically presenting as cutaneous, inhalational, or gastrointestinal forms. - It does **not form filamentous structures** and is not acid-fast, and its clinical presentation of rapid-onset severe pneumonia or skin lesions does not match the described chronic progressive illness with multiple abscesses. *Mycobacterium tuberculosis* - *Mycobacterium tuberculosis* causes **tuberculosis**, characterized by cough, weight loss, and night sweats, and can cause lung and brain abscesses (tuberculomas). - However, *Mycobacterium* species are **strongly acid-fast** due to their mycolic acid cell wall and are not described as gram-positive filamentous organisms.

Question 9: In severe CNS infections in children with complications, treatment may include:

A. IV Ig
B. Ventilation
C. Plasmapheresis
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - Treatment for **severe and complicated CNS infections** in children often requires a **multi-pronged approach** beyond antimicrobial therapy to manage severe neurological impairment, respiratory compromise, and immune-mediated complications. - Depending on the severity and specific infection, **IV Ig**, **ventilation**, and **plasmapheresis** may all be necessary adjunctive interventions to support the child and combat inflammation/autoimmune components. - **Note:** Primary treatment includes appropriate antimicrobials (antibiotics/antivirals), but this question focuses on adjunctive therapies for complicated cases. *IV Ig* - **Intravenous immunoglobulins (IV Ig)** are used in severe CNS infections with immune-mediated components, particularly **autoimmune encephalitis**, **post-infectious encephalomyelitis (ADEM)**, or severe viral encephalitis. - IV Ig modulates the immune response and may reduce neurological damage in specific scenarios. *Ventilation* - **Mechanical ventilation** is crucial for patients with severe CNS infections who develop respiratory compromise due to **brainstem dysfunction**, **refractory seizures**, **increased intracranial pressure** leading to hypoventilation, or **decreased consciousness** (GCS ≤8). - Essential for respiratory support and maintaining adequate oxygenation/ventilation in critically ill patients. *Plasmapheresis* - **Plasmapheresis** (plasma exchange) is used in specific CNS infections with **autoimmune or highly inflammatory components**, such as **autoimmune encephalitis**, **acute disseminated encephalomyelitis (ADEM)**, or **severe CNS vasculitis**. - Removes harmful autoantibodies and inflammatory mediators from circulation, particularly when IV Ig is insufficient.

Question 10: Which of the following is the MOST accurate statement about CSF?

A. Formed by the choroid plexus in the ventricles. (Correct Answer)
B. Normally contains no neutrophils
C. pH is less than that of plasma
D. Removal of CSF during dural tap can cause a headache due to the change in pressure.

Explanation: ***Formed by the choroid plexus in the ventricles.*** * The **choroid plexus**, located in the ventricles of the brain, is primarily responsible for the production of **cerebrospinal fluid (CSF)**. * Specialized epithelial cells of the choroid plexus filter blood plasma to produce CSF, which then circulates through the central nervous system. *Normally contains no neutrophils* * Normal CSF should contain **virtually no neutrophils**; their presence typically indicates an inflammatory or infectious process, such as **bacterial meningitis**. * While normal CSF doesn't have neutrophils, this option isn't as broadly accurate as the choroid plexus statement because the presence of other cell types like lymphocytes in small numbers is normal. *pH is less than that of plasma* * The pH of CSF is typically **slightly lower than that of plasma** (around 7.31 compared to 7.40), but the statement "less than" is broad and the degree of difference can be variable and is a less defining characteristic than its formation site. * This slight difference in pH is important for regulating **respiration** through chemoreceptors, but it's not the most accurate or fundamental statement about CSF properties. *Removal of CSF during dural tap can cause a headache due to the change in pressure.* * A **post-dural puncture headache** (PDPH) is a well-known complication of a dural tap (lumbar puncture), caused by the leakage of CSF from the puncture site, leading to **intracranial hypotension**, not simply a change in pressure. * This decrease in CSF volume and pressure causes a traction on pain-sensitive structures within the cranium, resulting in a headache that is typically **worse when upright** and relieved by lying down.

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