Infectious Diseases Practice Questions

Q: A previously healthy 43-year-old man presents with symptoms of cough, fever, weight loss, and lymphadenopathy for the past 2 months. His physical examination reveals multiple axillary and cervical lymph nodes and oropharyngeal ulcerations. His CXR reveals fibronodular pulmonary infiltrates in the apex, his sputum is negative for TB, and the HIV test is negative. A bronchoalveolar lavage (BAL) confirms the diagnosis. For the above patient, select the most likely diagnosis?

histoplasmosis. **Explanation:** The clinical presentation of chronic cough, fever, weight loss, and apical fibronodular infiltrates closely mimics pulmonary tuberculosis [1]. However, the presence of **oropharyngeal ulcerations** and generalized **lymphadenopathy** in a TB-negative patient is a classic hallmark of **Histoplasmosis** (*Histoplasma capsulatum*). 1. **Why Histoplasmosis is correct:** While often associated with immunocompromised states (HIV), Histoplasmosis can occur in immunocompetent individuals. It is a dimorphic fungus that primarily affects the lungs but can disseminate to the reticuloendothelial system (lymph nodes, liver, spleen) and mucous membranes. Oropharyngeal ulcers are a high-yield diagnostic clue for disseminated or chronic histoplasmosis. 2. **Why other options are incorrect:** * **Brucellosis:** Typically presents with undulant fever, arthralgia, and hepatosplenomegaly, but does not usually cause apical pulmonary infiltrates or oropharyngeal ulcers. * **Coccidioidomycosis:** Known as "Valley Fever," it causes pulmonary symptoms and erythema nodosum, but oropharyngeal ulceration is not a characteristic feature. * **Leprosy:** While it involves skin and nerves, it does not present with apical pulmonary fibronodular infiltrates or acute systemic symptoms like weight loss and fever mimicking TB [2]. **NEET-PG High-Yield Pearls:** * **The "Great Mimicker":** Histoplasmosis is the fungal equivalent of Tuberculosis. * **Morphology:** On biopsy/BAL, look for **small intracellular yeast cells** within macrophages (Gomori Methenamine Silver stain). * **Habitat:** Associated with **bird or bat droppings** (caving, cleaning chicken coops). * **Treatment:** Mild cases may resolve spontaneously; moderate-to-severe cases require **Itraconazole**, while disseminated disease requires **Amphotericin B**.

Q: A double rise of temperature in 24 hours is characteristic of which of the following conditions?

Kala Azar. **Explanation:** The characteristic fever pattern described as a **"double rise of temperature in 24 hours"** (bimodal fever) is a classic clinical sign of **Kala-azar (Visceral Leishmaniasis)**, caused by *Leishmania donovani*. This occurs when the patient experiences two distinct peaks of high-grade fever within a single day. **Analysis of Options:** * **Kala-azar (Correct):** Along with the double-quotidian fever, it is characterized by the triad of massive splenomegaly, hepatomegaly, and pancytopenia. The fever is often associated with "Kala-azar" (Black Sickness) due to hyperpigmentation of the skin. * **Malaria:** Typically presents with a **paroxysmal fever** (Cold, Hot, and Sweating stages). Depending on the species, the spikes occur every 48 hours (*P. vivax/falciparum* - Tertian) or 72 hours (*P. malariae* - Quartan), but not twice in one day. * **Tuberculosis:** Classically presents with an **evening rise of temperature** (low-grade) accompanied by night sweats. * **Hodgkin’s Lymphoma:** Associated with **Pel-Ebstein fever**, where periods of high fever alternate with afebrile periods lasting days to weeks. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in splenic or bone marrow aspirates. * **Serology:** RK-39 antigen-based dipstick test is the most common screening tool. * **Drug of Choice:** Liposomal Amphotericin B. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A non-ulcerative skin condition appearing years after "cured" visceral leishmaniasis, acting as a reservoir for the parasite.

Q: Basal exudates, infarcts, and hydrocephalus are findings observed in brain imaging studies. The most likely diagnosis is:

Tubercular Meningitis. ### Explanation The correct answer is **Tubercular Meningitis (TBM)**. This diagnosis is characterized by a classic triad of neuroimaging findings: 1. **Basal Exudates:** *Mycobacterium tuberculosis* has a predilection for the base of the brain. The inflammatory response leads to thick, gelatinous exudates in the basal cisterns, which can entrap cranial nerves [1]. 2. **Infarcts:** The intense inflammation causes **Vasculitis** (specifically affecting the Circle of Willis), leading to ischemic strokes, most commonly in the basal ganglia and internal capsule (Medial Striate artery territory). 3. **Hydrocephalus:** Exudates obstruct the flow of CSF at the level of the aqueduct or the basal cisterns, leading to **communicating or non-communicating hydrocephalus**. #### Why the other options are incorrect: * **Viral Meningitis:** Typically presents with normal imaging or mild meningeal enhancement. It does not cause thick exudates or infarcts. * **Herpes Encephalitis (HSV-1):** Characteristically involves the **temporal lobes** and limbic system. Imaging shows edema and hemorrhage in the temporal/frontal lobes, not basal exudates. * **Cerebral Malaria:** Imaging is often normal or shows diffuse cerebral edema. While micro-hemorrhages (Durck’s granulomas) can occur, the classic triad of TBM is absent. #### NEET-PG High-Yield Pearls: * **Gold Standard Diagnosis:** CSF Culture (MGIT) or GeneXpert (NAAT). * **CSF Findings in TBM:** High protein, low sugar, and **lymphocytic pleocytosis** [1]. * **Hydrocephalus Management:** Often requires a VP shunt; steroids (Dexamethasone) are added to ATT to reduce mortality and complications from exudates. * **Stage of TBM:** The presence of infarcts or altered sensorium usually indicates Stage II or III disease.

Q: Apex of the lung is commonly involved by which pathogen?

Klebsiella. **Explanation:** **Why Klebsiella is Correct:** *Klebsiella pneumoniae* is a Gram-negative encapsulated bacillus that typically causes severe, necrotizing lobar pneumonia. It has a strong predilection for the **upper lobes**, particularly the **apex of the lung**. This is attributed to the organism's tendency to cause infection in patients with impaired host defenses (e.g., chronic alcoholics, diabetics), where aspiration of oropharyngeal flora occurs [1]. The resulting inflammatory response is so intense that it leads to "bulging fissures" on X-ray due to heavy alveolar exudate. **Analysis of Incorrect Options:** * **Chlamydia:** *Chlamydia pneumoniae* typically causes "atypical pneumonia" characterized by diffuse, patchy interstitial infiltrates rather than localized apical consolidation [1]. * **Coxiella burnetii:** The causative agent of Q fever usually presents with non-specific radiological findings, most commonly multiple rounded opacities or segmental consolidation in the **lower lobes**. * **Actinomyces israelii:** While *Actinomyces* can cross anatomical boundaries and involve the pleura or chest wall, it most commonly involves the **lower lobes** via aspiration [1]. It is known for causing "sulfur granules" in abscesses rather than isolated apical pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **"Currant Jelly" Sputum:** A classic board-style descriptor for *Klebsiella* pneumonia due to blood and mucus. * **Friedländer’s Pneumonia:** An older eponym for *Klebsiella* pneumonia. * **Differential Diagnosis for Apical Lesions:** Remember the mnemonic **"SET"** for upper lobe involvement: **S**ilicosis, **E**xtrinsic allergic alveolitis, and **T**uberculosis (the most common cause of apical cavitary lesions). *Klebsiella* is the classic bacterial (non-TB) cause. * **Alcoholism Link:** Always suspect *Klebsiella* in an alcoholic patient presenting with sudden onset of productive cough and upper lobe consolidation [1].

Q: Botulism causes which of the following clinical manifestations?

Descending flaccid paralysis. **Explanation:** **Botulism** is caused by the neurotoxin produced by *Clostridium botulinum*. The underlying pathophysiology involves the toxin irreversibly binding to the presynaptic nerve terminals, where it cleaves SNARE proteins. This prevents the release of **acetylcholine (ACh)** at the neuromuscular junction. Since ACh is the primary excitatory neurotransmitter for muscle contraction, its absence leads to **flaccid paralysis**. The clinical hallmark of botulism is a **symmetric, descending paralysis**. It typically begins with cranial nerve involvement (the "4 Ds": Diplopia, Dysarthria, Dysphagia, and Dysphonia) and progresses downward to involve the trunk, upper extremities, and finally the lower extremities and respiratory muscles. **Analysis of Incorrect Options:** * **Descending spastic paralysis:** Spasticity occurs when there is a loss of inhibitory control (e.g., Tetanus). Botulism causes a loss of excitation, leading to flaccidity, not spasticity. * **Ascending paralysis:** This is characteristic of **Guillain-Barré Syndrome (GBS)** or Tick Paralysis, where weakness starts in the lower extremities and moves upward. * **Ascending spastic paralysis:** This pattern is not typically seen in acute bacterial toxemias. **High-Yield Clinical Pearls for NEET-PG:** * **Infant Botulism:** Known as "Floppy Baby Syndrome," usually caused by ingestion of **honey** containing spores (colonization of the gut). * **Foodborne Botulism:** Caused by ingestion of **pre-formed toxin** in improperly canned alkaline foods. * **Diagnosis:** Primarily clinical; confirmed by demonstrating toxin in serum, stool, or food via the Mouse Neutralization Test (Gold Standard). * **Treatment:** Equine antitoxin (for adults) or Human Botulism Immune Globulin (for infants). Support with mechanical ventilation is critical.

Q: Which of the following characterizes amebic liver disease?

Most common in the right lobe of the liver. **Explanation:** Amebic liver abscess (ALA) is the most common extra-intestinal manifestation of infection by *Entamoeba histolytica*. **Why Option A is Correct:** The **right lobe of the liver** is involved in approximately 70–80% of cases. This predilection occurs because the right lobe receives the bulk of the venous drainage from the superior mesenteric vein (which drains the cecum and ascending colon, the primary sites of intestinal amebiasis) via a "streaming" effect in the portal circulation. **Why the Other Options are Incorrect:** * **Option B:** While ALA is a complication of intestinal amebiasis, **fever and right upper quadrant pain** are the most common presentations. Diarrhea is present in less than one-third of patients at the time of diagnosis [1]. * **Option C:** ALA is highly sensitive to nitroimidazoles. **Metronidazole** (or Tinidazole) remains the drug of choice [2], followed by a luminal amebicide (like Paromomycin) to eradicate the intestinal cyst stage. * **Option D:** The **colon** (large intestine) is the primary site of infection [1]. The liver is the most common *extra-intestinal* site, reached via the portal venous system. **NEET-PG High-Yield Pearls:** * **Demographics:** Most common in adult males (10:1 ratio), often associated with chronic alcohol consumption. * **Aspirate:** Classically described as **"Anchovy sauce"** appearance (odorless, reddish-brown, consisting of necrotic hepatocytes) [1]. * **Imaging:** Usually presents as a solitary abscess. * **Diagnosis:** Serology (ELISA) is highly sensitive; ultrasound is the initial imaging of choice. * **Treatment:** Medical management is successful in >90% of cases; needle aspiration is only indicated if the abscess is large (>10cm), at risk of rupture (left lobe), or fails to respond to antibiotics [2].

Question 1

A previously healthy 43-year-old man presents with symptoms of cough, fever, weight loss, and lymphadenopathy for the past 2 months. His physical examination reveals multiple axillary and cervical lymph nodes and oropharyngeal ulcerations. His CXR reveals fibronodular pulmonary infiltrates in the apex, his sputum is negative for TB, and the HIV test is negative. A bronchoalveolar lavage (BAL) confirms the diagnosis. For the above patient, select the most likely diagnosis?

Accepted Answer

histoplasmosis

Answer

brucellosis

Answer

coccidioidomycosis

Answer

leprosy

Question 2

A patient on a urinary catheter has a catheter tip culture that shows extended-spectrum beta-lactamase (ESBL)-positive Klebsiella. Which of the following drugs can be given?

Accepted Answer

A beta-lactamase inhibitor

Answer

Ceftriaxone

Answer

Aminoglycoside

Answer

Tetracycline

Question 3

A double rise of temperature in 24 hours is characteristic of which of the following conditions?

Accepted Answer

Kala Azar

Answer

Malaria

Answer

Tuberculosis

Answer

Hodgkin's lymphoma

Question 4

Which of the following is NOT true about Pneumocystis jirovecii pneumonia?

Accepted Answer

Associated with an increased alveolar-arterial oxygen gradient (PAO2 - PaO2)

Answer

Characterized by respiratory alkalosis

Answer

Associated with decreased diffusion capacity

Answer

Leads to cyanosis

Question 5

Basal exudates, infarcts, and hydrocephalus are findings observed in brain imaging studies. The most likely diagnosis is:

Accepted Answer

Tubercular Meningitis

Answer

Viral Meningitis

Answer

Herpes encephalitis

Answer

Cerebral Malaria

Question 6

Which of the following is the best method to evaluate alpha interferon therapy for Hepatitis C Virus (HCV) infection?

Accepted Answer

Quantification of HCV RNA

Answer

ALT and AST levels

Answer

Serum bilirubin level

Answer

Serum IgM and IgG levels

Question 7

Apex of the lung is commonly involved by which pathogen?

Accepted Answer

Klebsiella

Answer

Chlamydia

Answer

Coxiella burnetti

Answer

Actinomyces israelii

Question 8

Botulism causes which of the following clinical manifestations?

Accepted Answer

Descending flaccid paralysis

Answer

Descending spastic paralysis

Answer

Ascending paralysis

Answer

Ascending spastic paralysis

Question 9

Which of the following statements regarding HIV-associated TB is FALSE?

Accepted Answer

Patients with both HIV infection and TB are more infectious than persons without HIV co-infection.

Answer

Extrapulmonary TB is common among HIV-infected patients.

Answer

The diagnosis of TB in HIV-infected patients may be difficult.

Answer

Immune reconstitution inflammatory syndrome (IRIS) is more common among patients with advanced immunosuppression and extrapulmonary TB.

Question 10

Which of the following characterizes amebic liver disease?

Accepted Answer

Most common in the right lobe of the liver

Answer

Diarrhea is the most common presentation

Answer

Resistant to metronidazole

Answer

The liver is the most common primary site of infection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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