NRTI, NNRTI, PI, INSTI, and entry inhibitors — MCQs

10 questions

A 37-year-old man comes to the physician because of a 6-month history of progressive breast enlargement. Two years ago, he was diagnosed with HIV infection and started treatment with antiretroviral medications. Examination shows a soft, non-tender, ill-defined swelling at the nape of the neck. The cheeks appear hollowed. Serum studies show increased total cholesterol and LDL concentration. Which of the following medications is the most likely cause of these findings?

A physician scientist is looking for a more efficient way to treat HIV. Patients infected with HIV mount a humoral immune response by producing antibodies against the HIV envelope proteins. These antibodies are the same antibodies detected by the ELISA and western blot assays used to diagnose the disease. The physician scientist is trying to generate a new, more potent antibody against the same HIV envelope proteins targeted by the natural humoral immune response. Of the following proteins, which is the most likely target of the antibody he is designing?

A 23-year-old male with a homozygous CCR5 mutation is found to be immune to HIV infection. The patient’s CCR5 mutation interferes with the function of which viral protein?

A 44-year-old man comes to the physician for a follow-up examination. Eight months ago, he was diagnosed with HIV infection and combined antiretroviral treatment was begun. He feels well. He does not smoke or drink alcohol. Current medications include lamivudine, zidovudine, atazanavir, and trimethoprim-sulfamethoxazole. Laboratory studies show: Hemoglobin 11.2 g/dL Mean corpuscular volume 102 μm3 Leukocyte count 2,600/mm3 Segmented neutrophils 38% Lymphocytes 54% Platelet count 150,000/mm3 Serum Folate normal Lactate 6.0 mEq/L (N = 0.5–2.2) Arterial blood gas analysis on room air shows: pH 7.34 pCO2 55 mm Hg pO2 99 mmHg HCO3- 14 mEq/L The drug most likely responsible for this patient's current laboratory findings belongs to which of the following classes of drugs?

A 35-year-old man comes to the physician because of a 6-month history of fatigue and increased sweating at night. He says that he feels “constantly tired” and needs more rest than usual although he sleeps well. In the morning, his sheets are often wet and his skin is clammy. He has not had any sore throat, runny nose, or cough recently. He has not traveled anywhere. Over the past 4 months, he has had a 6.8-kg (15-lb) weight loss, despite having a normal appetite. He does not drink or urinate more than usual. He is 181 cm (5 ft 11 in) tall and weighs 72 kg (159 lb); BMI is 22 kg/m2. His temperature is 37.9°C (100.2°F), pulse is 65/min, and blood pressure is 120/70 mm Hg. Physical examination shows no abnormalities. An HIV screening test and confirmatory test are both positive. The CD4 count is 600 cells/μl and the viral load is 104 copies/mL. Treatment with lamivudine, zidovudine, and indinavir is begun. The patient is at greatest risk for which of the following adverse effects?

A 29-year-old female presents to her gynecologist complaining of a painful rash around her genitals. She has multiple sexual partners and uses condoms intermittently. Her last STD screen one year ago was negative. On examination, she has bilateral erosive vesicles on her labia majora and painful inguinal lymphadenopathy. She is started on an oral medication that requires a specific thymidine kinase for activation. Which of the following adverse effects is associated with this drug?

An HIV-positive patient with a CD4+ count of 45 is receiving recommended first-line treatment for a case of cytomegalovirus retinitis. Coadministration with which of the following agents would be most likely to precipitate a deficiency of neutrophils in this patient?

An investigator is studying the mechanism of HIV infection in cells obtained from a human donor. The effect of a drug that impairs viral fusion and entry is being evaluated. This drug acts on a protein that is cleaved off of a larger glycosylated protein in the endoplasmic reticulum of the host cell. The protein that is affected by the drug is most likely encoded by which of the following genes?

Four scientists were trying to measure the effect of a new inhibitor X on the expression levels of transcription factor, HNF4alpha. They measured the inhibition levels by using RT-qPCR. In short they converted the total mRNA of the cells to cDNA (RT part), and used PCR to amplify the cDNA quantifying the amplification with a dsDNA binding dye (qPCR part). Which of the following group characteristics contains a virus(es) that has the enzyme necessary to convert the mRNA to cDNA used in the above scenario?

Q10

A 44-year-old with a past medical history significant for human immunodeficiency virus infection presents to the emergency department after he was found to be experiencing worsening confusion. The patient was noted to be disoriented by residents and staff at the homeless shelter where he resides. On presentation he reports headache and muscle aches but is unable to provide more information. His temperature is 102.2°F (39°C), blood pressure is 112/71 mmHg, pulse is 115/min, and respirations are 24/min. Knee extension with hips flexed produces significant resistance and pain. A lumbar puncture is performed with the following results: Opening pressure: Normal Fluid color: Clear Cell count: Increased lymphocytes Protein: Slightly elevated Which of the following is the most likely cause of this patient's symptoms?

NRTI, NNRTI, PI, INSTI, and entry inhibitors US Medical PG Practice Questions and MCQs

Question 1: A 37-year-old man comes to the physician because of a 6-month history of progressive breast enlargement. Two years ago, he was diagnosed with HIV infection and started treatment with antiretroviral medications. Examination shows a soft, non-tender, ill-defined swelling at the nape of the neck. The cheeks appear hollowed. Serum studies show increased total cholesterol and LDL concentration. Which of the following medications is the most likely cause of these findings?

A. Nevirapine
B. Indinavir (Correct Answer)
C. Enfuvirtide
D. Abacavir
E. Raltegravir

Explanation: ***Indinavir*** - This patient presents with signs of **lipodystrophy**, specifically **lipoaccumulation** (breast enlargement, "buffalo hump" at the nape of the neck) and **lipoatrophy** (hollow cheeks), along with **dyslipidemia**. - **Protease inhibitors (PIs)**, such as indinavir, are well-known to cause these metabolic complications, including **lipodystrophy** and **hyperlipidemia**, in patients with HIV. *Nevirapine* - Nevirapine is a **non-nucleoside reverse transcriptase inhibitor (NNRTI)**. - While NNRTIs can be associated with some metabolic side effects, they are less commonly implicated in severe **lipodystrophy** and **dyslipidemia** compared to protease inhibitors. *Enfuvirtide* - Enfuvirtide is a **fusion inhibitor** and generally has a favorable metabolic profile. - It is not typically associated with **lipodystrophy** or significant **dyslipidemia**. *Abacavir* - Abacavir is a **nucleoside reverse transcriptase inhibitor (NRTI)**. - While some NRTIs (especially stavudine and zidovudine) were strongly linked to lipoatrophy, abacavir is much less likely to cause this severe form of **lipodystrophy** or **hyperlipidemia**. *Raltegravir* - Raltegravir is an **integrase strand transfer inhibitor (INSTI)**. - INSTIs are increasingly used due to their generally good metabolic profile and are not a common cause of **lipodystrophy** or **dyslipidemia**.

Question 2: A physician scientist is looking for a more efficient way to treat HIV. Patients infected with HIV mount a humoral immune response by producing antibodies against the HIV envelope proteins. These antibodies are the same antibodies detected by the ELISA and western blot assays used to diagnose the disease. The physician scientist is trying to generate a new, more potent antibody against the same HIV envelope proteins targeted by the natural humoral immune response. Of the following proteins, which is the most likely target of the antibody he is designing?

A. p24
B. CXCR4
C. CCR5
D. p17
E. gp120 (Correct Answer)

Explanation: ***gp120*** - **gp120** is an **envelope glycoprotein** on the surface of HIV, responsible for binding to CD4 receptors on host cells. - Antibodies against **gp120** are generated during natural infection and are detected by diagnostic assays, making it a primary target for therapeutic antibody development. *p24* - **p24** is a **capsid protein** of HIV, forming the conical core of the virus, but it is not an envelope protein. - While antibodies against **p24** are produced during infection and are detectable, it's an internal protein, not exposed on the viral surface for direct neutralization. *CXCR4* - **CXCR4** is a **chemokine co-receptor** found on the surface of host cells (e.g., T-lymphocytes), used by some HIV strains (T-tropic) for entry. - It is a host cell protein, not an HIV viral protein, so it would not be a target for antibodies aiming to directly neutralize the virus. *CCR5* - **CCR5** is another **chemokine co-receptor** on host cells (e.g., macrophages, T-lymphocytes) used by other HIV strains (M-tropic) for viral entry. - Similar to CXCR4, it is a host cell protein, not an HIV envelope protein, and therefore not a direct target for neutralizing antibodies against the virus itself. *p17* - **p17** is an HIV **matrix protein** located just beneath the viral envelope, playing a role in viral assembly and budding. - Similar to p24, it is an internal structural protein, not an external envelope protein, making it less accessible for neutralizing antibodies.

Question 3: A 23-year-old male with a homozygous CCR5 mutation is found to be immune to HIV infection. The patient’s CCR5 mutation interferes with the function of which viral protein?

A. gp41
B. Reverse transcriptase
C. pp17
D. gp120 (Correct Answer)
E. p24

Explanation: ***gp120*** - The **gp120 protein** on the HIV envelope is responsible for binding to the **CD4 receptor** and the **coreceptor CCR5** or CXCR4 on host cells, which is the initial step for viral entry. - A homozygous **CCR5 mutation** (specifically the **CCR5-Δ32** deletion) prevents HIV from using this coreceptor, thereby blocking the binding of gp120 and subsequent viral entry. *gp41* - **gp41** is another envelope protein that, after gp120 binds to CD4 and a coreceptor, undergoes a conformational change to mediate **fusion** of the viral and host cell membranes. - While essential for entry, gp41 acts downstream of gp120's primary binding to the coreceptor, so a CCR5 mutation primarily affects gp120's ability to engage with the cell. *Reverse transcriptase* - **Reverse transcriptase** is a viral enzyme responsible for **converting viral RNA into DNA** once the virus has already entered the host cell cytoplasm. - A CCR5 mutation prevents viral entry, thus the activity of reverse transcriptase is not directly interfered with by the mutation itself but rather by the lack of cellular access. *pp17* - **pp17**, also known as **matrix protein**, is an internal structural protein that plays a role in the assembly of new virions and guiding the **reverse transcribed DNA** into the nucleus. - This protein is involved in later stages of the viral life cycle *after* entry and integration, and its function is not directly blocked by a CCR5 mutation. *p24* - **p24** is the major **capsid protein** that forms the core of the HIV virus, enclosing the viral RNA and enzymes. - It is critical for maintaining the structural integrity of the virus and is a key target for diagnostic tests, but it does not directly participate in the initial binding and entry process that is affected by a CCR5 mutation.

Question 4: A 44-year-old man comes to the physician for a follow-up examination. Eight months ago, he was diagnosed with HIV infection and combined antiretroviral treatment was begun. He feels well. He does not smoke or drink alcohol. Current medications include lamivudine, zidovudine, atazanavir, and trimethoprim-sulfamethoxazole. Laboratory studies show: Hemoglobin 11.2 g/dL Mean corpuscular volume 102 μm3 Leukocyte count 2,600/mm3 Segmented neutrophils 38% Lymphocytes 54% Platelet count 150,000/mm3 Serum Folate normal Lactate 6.0 mEq/L (N = 0.5–2.2) Arterial blood gas analysis on room air shows: pH 7.34 pCO2 55 mm Hg pO2 99 mmHg HCO3- 14 mEq/L The drug most likely responsible for this patient's current laboratory findings belongs to which of the following classes of drugs?

A. Entry inhibitor
B. Dihydrofolate reductase inhibitor
C. Nucleoside reverse transcriptase inhibitor (Correct Answer)
D. Integrase inhibitor
E. Protease inhibitor

Explanation: ***Nucleoside reverse transcriptase inhibitor*** - The patient presents with **macrocytic anemia** (Hgb 11.2, MCV 102), **leukopenia** (2600), **lactic acidosis** (lactate 6.0, pH 7.34, HCO3- 14, pCO2 55), and is on a regimen including **zidovudine** and **lamivudine**. - **Zidovudine** (AZT), a nucleoside reverse transcriptase inhibitor (NRTI), is well-known for causing **myelosuppression** (anemia, leukopenia) and **mitochondrial toxicity**, which can lead to lactic acidosis due to impaired oxidative phosphorylation. *Entry inhibitor* - Entry inhibitors like **enfuvirtide** and **maraviroc** block HIV from entering CD4+ cells; side effects are mainly injection site reactions or hepatotoxicity. - They are not associated with macrocytic anemia, leukopenia, or lactic acidosis. *Dihydrofolate reductase inhibitor* - **Trimethoprim-sulfamethoxazole (TMP-SMX)**, listed as a current medication, is a dihydrofolate reductase inhibitor that can cause **bone marrow suppression** mimicking folate deficiency. - However, the patient's folate levels are normal, and the significant lactic acidosis points away from TMP-SMX as the primary cause of all findings. *Integrase inhibitor* - Integrase inhibitors like **raltegravir** or **dolutegravir** prevent the integration of viral DNA into the host genome. - Their primary side effects are typically gastrointestinal (nausea, diarrhea), headache, or insomnia, and they do not cause macrocytic anemia, leukopenia, or lactic acidosis. *Protease inhibitor* - **Atazanavir**, a protease inhibitor from the patient's regimen, can cause **hyperbilirubinemia** and **lipodystrophy** but is not directly linked to the bone marrow suppression and severe lactic acidosis seen here. - Other protease inhibitors can cause metabolic complications, but not this specific constellation of hematologic and metabolic abnormalities.

Question 5: A 35-year-old man comes to the physician because of a 6-month history of fatigue and increased sweating at night. He says that he feels “constantly tired” and needs more rest than usual although he sleeps well. In the morning, his sheets are often wet and his skin is clammy. He has not had any sore throat, runny nose, or cough recently. He has not traveled anywhere. Over the past 4 months, he has had a 6.8-kg (15-lb) weight loss, despite having a normal appetite. He does not drink or urinate more than usual. He is 181 cm (5 ft 11 in) tall and weighs 72 kg (159 lb); BMI is 22 kg/m2. His temperature is 37.9°C (100.2°F), pulse is 65/min, and blood pressure is 120/70 mm Hg. Physical examination shows no abnormalities. An HIV screening test and confirmatory test are both positive. The CD4 count is 600 cells/μl and the viral load is 104 copies/mL. Treatment with lamivudine, zidovudine, and indinavir is begun. The patient is at greatest risk for which of the following adverse effects?

A. Urolithiasis (Correct Answer)
B. Stevens-Johnson syndrome
C. Hypersensitivity reaction
D. Chronic kidney disease
E. Pancreatitis

Explanation: ***Urolithiasis*** - The patient is receiving **indinavir**, a protease inhibitor known to cause **nephrolithiasis** (kidney stones) due to the drug's poor solubility. - Patients on indinavir should be well-hydrated to reduce the risk of stone formation. *Stevens-Johnson syndrome* - This severe skin reaction is more commonly associated with non-nucleoside reverse transcriptase inhibitors (NNRTIs) like **nevirapine** and **efavirenz**, or with sulfonamide antibiotics, rather than indinavir. - While possible with many drugs, it is not the *greatest risk* among the options for this specific regimen. *Hypersensitivity reaction* - While hypersensitivity can occur with many drugs, particularly abacavir (an NRTI not included in this regimen), it is not the most prominent or specific adverse effect for the given combination, especially indinavir. - Symptoms usually include fever, rash, and multi-organ involvement, which can be acute. *Chronic kidney disease* - While some antiretrovirals, particularly **tenofovir disoproxil fumarate (TDF)**, can cause renal tubular dysfunction and lead to chronic kidney disease, TDF is not part of this patient's regimen. - Indinavir's primary renal complication is acute stone formation, not typically chronic kidney disease in the absence of pre-existing conditions or other nephrotoxic drugs. *Pancreatitis* - Pancreatitis is a known adverse effect of some NRTIs, particularly **didanosine** and **stavudine**, neither of which are in this patient's treatment plan. - Lamivudine and zidovudine have a lower risk of pancreatitis compared to other NRTIs.

Question 6: A 29-year-old female presents to her gynecologist complaining of a painful rash around her genitals. She has multiple sexual partners and uses condoms intermittently. Her last STD screen one year ago was negative. On examination, she has bilateral erosive vesicles on her labia majora and painful inguinal lymphadenopathy. She is started on an oral medication that requires a specific thymidine kinase for activation. Which of the following adverse effects is associated with this drug?

A. Photosensitivity
B. Deafness
C. Renal failure (Correct Answer)
D. Gingival hyperplasia
E. Pulmonary fibrosis

Explanation: ***Renal failure*** - The patient's symptoms (painful genital rash, erosive vesicles, inguinal lymphadenopathy) are highly suggestive of **herpes simplex virus (HSV) infection**, likely genital herpes. - The drug described is an antiviral agent like **acyclovir, valacyclovir, or famciclovir**, which require **viral thymidine kinase** for activation and are known to cause **renal impairment** (nephrotoxicity) as an adverse effect, especially with high doses or in dehydrated patients due to crystal nephropathy. *Photosensitivity* - **Photosensitivity** is a common side effect of some antibiotics (e.g., tetracyclines, sulfonamides), diuretics (e.g., thiazides), and antifungals, but it is **not a prominent adverse effect of acyclovir or its derivatives**. - While theoretical, it is not a clinically significant or frequently observed adverse effect associated with the class of antiviral drugs used for HSV. *Deafness* - **Ototoxicity**, leading to deafness or hearing loss, is a well-known adverse effect of certain classes of drugs, such as **aminoglycoside antibiotics** (e.g., gentamicin) and **loop diuretics** (e.g., furosemide). - It is **not an adverse effect** associated with antiviral medications like acyclovir. *Gingival hyperplasia* - **Gingival hyperplasia** (overgrowth of gum tissue) is a recognized side effect of specific medications including **phenytoin** (an anticonvulsant), **cyclosporine** (an immunosuppressant), and **calcium channel blockers** (e.g., nifedipine, amlodipine). - This adverse effect is **not associated with antiviral drugs** used to treat herpes simplex. *Pulmonary fibrosis* - **Pulmonary fibrosis** is a serious adverse effect linked to various drugs like **amiodarone** (an antiarrhythmic), **bleomycin** (a chemotherapeutic agent), **methotrexate** (an immunosuppressant/chemotherapeutic), and **nitrofurantoin** (an antibiotic). - **Antiviral medications for HSV** do not typically cause pulmonary fibrosis.

Question 7: An HIV-positive patient with a CD4+ count of 45 is receiving recommended first-line treatment for a case of cytomegalovirus retinitis. Coadministration with which of the following agents would be most likely to precipitate a deficiency of neutrophils in this patient?

A. Ritonavir
B. Raltegravir
C. Foscarnet
D. Efavirenz
E. Zidovudine (Correct Answer)

Explanation: ***Zidovudine*** - **Zidovudine (AZT)** is a nucleoside reverse transcriptase inhibitor (NRTI) that is well-known for causing **myelosuppression**, particularly **neutropenia** and **anemia**. - In an HIV-positive patient with a low **CD4+ count** and concurrent treatment for **CMV retinitis** (which often involves drugs like ganciclovir that can also cause myelosuppression), adding zidovudine significantly increases the risk of severe neutropenia. *Ritonavir* - **Ritonavir** is a protease inhibitor primarily known for its role as a **pharmacokinetic booster** in HIV therapy, enhancing the levels of other antiretrovirals. - While it can cause gastrointestinal side effects and hepatotoxicity, **myelosuppression** and specifically neutropenia are not its primary or common adverse effects. *Raltegravir* - **Raltegravir** is an integrase strand transfer inhibitor (INSTI) generally well-tolerated with a favorable side effect profile. - Common side effects include headache, nausea, and fatigue, but it is **not typically associated with significant myelosuppression** or neutropenia. *Foscarnet* - **Foscarnet** is an antiviral agent used for treating CMV retinitis, particularly in cases of ganciclovir resistance. - Its major dose-limiting toxicities include **nephrotoxicity** and **electrolyte disturbances** (e.g., hypocalcemia, hypomagnesemia), not primarily neutropenia. *Efavirenz* - **Efavirenz** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) associated with central nervous system side effects such as dizziness, insomnia, and vivid dreams. - While skin rash and hepatotoxicity can occur, **bone marrow suppression** leading to neutropenia is not a characteristic or frequent adverse effect of efavirenz.

Question 8: An investigator is studying the mechanism of HIV infection in cells obtained from a human donor. The effect of a drug that impairs viral fusion and entry is being evaluated. This drug acts on a protein that is cleaved off of a larger glycosylated protein in the endoplasmic reticulum of the host cell. The protein that is affected by the drug is most likely encoded by which of the following genes?

A. gag
B. env (Correct Answer)
C. tat
D. pol
E. rev

Explanation: ***env*** - The **env (envelope) gene** of HIV encodes for the precursor protein **gp160**, which is then cleaved by host cellular proteases into **gp120** and **gp41** within the endoplasmic reticulum. - **gp120** and **gp41** together form the viral envelope glycoproteins responsible for viral binding to host cells and **fusion/entry**, making them the target of drugs that impair these processes. *gag* - The **gag (group-specific antigen) gene** encodes for structural proteins of the viral core, such as **p24 (capsid protein)**, p17 (matrix protein), and p7 (nucleocapsid protein). - These proteins are primarily involved in the assembly of new virions and do not directly mediate viral fusion and entry. *tat* - The **tat (trans-activator of transcription) gene** encodes a regulatory protein that significantly enhances the transcription of viral genes. - It plays a crucial role in the viral life cycle by increasing the efficiency of HIV gene expression, but it is not directly involved in viral fusion or entry. *pol* - The **pol (polymerase) gene** encodes for essential viral enzymes, including **reverse transcriptase**, integrase, and protease. - These enzymes are critical for converting viral RNA into DNA, integrating viral DNA into the host genome, and cleaving viral polyproteins, respectively, but they are not involved in mediating viral entry. *rev* - The **rev (regulator of virion expression) gene** encodes a regulatory protein that facilitates the transport of unspliced and partially spliced viral RNAs from the nucleus to the cytoplasm. - This transport is crucial for the synthesis of structural and enzymatic proteins and for packaging viral RNA into new virions, but it does not directly participate in viral fusion and entry.

Question 9: Four scientists were trying to measure the effect of a new inhibitor X on the expression levels of transcription factor, HNF4alpha. They measured the inhibition levels by using RT-qPCR. In short they converted the total mRNA of the cells to cDNA (RT part), and used PCR to amplify the cDNA quantifying the amplification with a dsDNA binding dye (qPCR part). Which of the following group characteristics contains a virus(es) that has the enzyme necessary to convert the mRNA to cDNA used in the above scenario?

A. Enveloped, dimeric (+) ssRNA (Correct Answer)
B. Enveloped, circular (-) ssRNA
C. Nonenveloped, (+) ssRNA
D. Nonenveloped, ssDNA
E. Nonenveloped, circular dsDNA

Explanation: ***Enveloped, dimeric (+) ssRNA*** - This group describes **retroviruses**, which possess the enzyme **reverse transcriptase**. - **Reverse transcriptase** is essential for converting their **RNA genome** into **cDNA**, a process analogous to the RT step in RT-qPCR. - Examples include **HIV**, which is tagged to this topic. *Enveloped, circular (-) ssRNA* - This description does not accurately represent a major viral family. - Most enveloped negative-sense RNA viruses have **linear or segmented genomes** (e.g., **Orthomyxoviruses**, **Bunyaviruses**), not circular. - These viruses replicate using an **RNA-dependent RNA polymerase** to synthesize mRNA from their negative-sense RNA genome. - They do not inherently carry or require **reverse transcriptase** for their life cycle. *Nonenveloped, (+) ssRNA* - These viruses, like **Picornaviruses**, directly use their positive-sense RNA as mRNA and replicate via an **RNA-dependent RNA polymerase**. - They do not possess **reverse transcriptase** for cDNA synthesis. *Nonenveloped, ssDNA* - Viruses with a **single-stranded DNA genome**, such as **Parvoviruses**, replicate by first synthesizing a double-stranded DNA intermediate. - Their replication machinery does not involve **reverse transcriptase** to convert RNA to DNA. *Nonenveloped, circular dsDNA* - Viruses in this group, like **Papillomaviruses** and **Polyomaviruses**, have a circular double-stranded DNA genome and replicate within the host nucleus using the host's DNA polymerase. - They do not utilize or encode **reverse transcriptase** for their replication cycle.

Question 10: A 44-year-old with a past medical history significant for human immunodeficiency virus infection presents to the emergency department after he was found to be experiencing worsening confusion. The patient was noted to be disoriented by residents and staff at the homeless shelter where he resides. On presentation he reports headache and muscle aches but is unable to provide more information. His temperature is 102.2°F (39°C), blood pressure is 112/71 mmHg, pulse is 115/min, and respirations are 24/min. Knee extension with hips flexed produces significant resistance and pain. A lumbar puncture is performed with the following results: Opening pressure: Normal Fluid color: Clear Cell count: Increased lymphocytes Protein: Slightly elevated Which of the following is the most likely cause of this patient's symptoms?

A. Herpes simplex virus
B. Group B streptococcus
C. Cryptococcus (Correct Answer)
D. Tuberculosis
E. Neisseria meningitidis

Explanation: ***Cryptococcus*** - **Cryptococcus neoformans** is the **most common cause of meningitis** in HIV-positive patients, particularly those with CD4 counts <100 cells/μL. - The CSF findings are **classic for cryptococcal meningitis**: clear fluid, **lymphocytic pleocytosis**, normal or mildly elevated opening pressure, and **slightly elevated protein** with normal or mildly decreased glucose. - The patient's **subacute presentation** with confusion, fever, and meningeal signs in the context of **HIV infection** strongly suggests cryptococcal meningitis as the most likely diagnosis. - Diagnosis is confirmed with **CSF cryptococcal antigen**, India ink stain, or fungal culture. *Herpes simplex virus* - While HSV can cause meningitis or encephalitis, it is **not the most common cause** of meningitis in HIV-positive patients. - **HSV encephalitis** typically presents with more prominent temporal lobe involvement, including personality changes, seizures, and focal neurological deficits. - HSV meningitis is more common in **immunocompetent individuals** and would be less likely than cryptococcal infection in an HIV patient. *Group B streptococcus* - This causes **bacterial meningitis** with a **neutrophilic predominance** in CSF, not lymphocytic. - CSF would show **markedly elevated protein**, **decreased glucose**, and cloudy appearance. - More common in neonates and elderly patients, not typically associated with HIV. *Neisseria meningitidis* - This is a cause of **acute bacterial meningitis** with rapid onset and often a **petechial rash**. - CSF would show **neutrophilic predominance**, **high protein**, **low glucose**, and turbid appearance. - The lymphocytic pleocytosis rules out typical bacterial meningitis. *Tuberculosis* - **Tuberculous (TB) meningitis** is an important consideration in HIV-positive patients and can present with lymphocytic pleocytosis. - However, TB meningitis typically shows **markedly elevated protein** (often >100 mg/dL, not "slightly elevated"), **low glucose** (<45 mg/dL), and may have a "spider-web clot" on standing CSF. - The **more subacute to chronic course** (weeks) and absence of very high protein make TB less likely than cryptococcal meningitis in this acute presentation.

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