Cerebrospinal Fluid Analysis — MCQs
Intrathecal fluorescein with endoscopic visualization is useful in diagnosis of?
When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?
Which of the following is the MOST accurate statement about CSF?
A patient comes to ED with fever and headache. On examination he has neck stiffness. CSF analysis was done: Glucose 55 mg/dl (normal 50-80), Protein 0.50 g/L (normal 0.18-0.45), ICT 35 cmH2O (normal 5-20), WBC 25 (predominantly lymphocytes). Most likely diagnosis is:
Xanthochromia of CSF is seen in all except:
Two or more oligoclonal bands in cerebrospinal fluid are most often positive in-
Which of the following does not require a lumbar puncture in children?
Which is the best fluid for postmortem investigation?
What is the normal intracranial pressure in a child (in mmH2O)?
Diagnosis of Gout is confirmed by which test?
Cerebrospinal Fluid Analysis Indian Medical PG Practice Questions and MCQs
Question 1: Intrathecal fluorescein with endoscopic visualization is useful in diagnosis of?
- A. Rhinitis Medicamentosa
- B. Multiple ethmoidal polyps
- C. Diagnosis of CSF Rhinorrhoea (Correct Answer)
- D. Deviated nasal septum
Explanation: ***Diagnosis of CSF Rhinorrhoea*** - **Intrathecal fluorescein** is instilled into the cerebrospinal fluid, and its presence in the nasal cavity via endoscopy confirms a **CSF leak**. - This method provides direct visualization of the leak site, which is crucial for surgical planning. *Rhinitis Medicamentosa* - This condition is caused by overuse of **topical decongestants** and characterized by nasal congestion, not a CSF leak. - Diagnosis is typically based on patient history and clinical examination rather than specialized imaging or dye studies. *Multiple ethmoidal polyps* - **Ethmoidal polyps** are benign growths in the ethmoid sinuses, causing nasal obstruction and anosmia. - Diagnosis is made via nasal endoscopy and CT scan, and fluorescein staining is not indicated. *Deviated nasal septum* - A **deviated nasal septum** is a structural abnormality causing unilateral or bilateral nasal obstruction. - Diagnosis is clinical and confirmed by anterior rhinoscopy or nasal endoscopy, with no role for intrathecal fluorescein.
Question 2: When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?
- A. The iliac crests (Correct Answer)
- B. The lowest pair of ribs bilaterally
- C. The inferior angles of the scapulae
- D. The posterior superior iliac spines
Explanation: ***The iliac crests*** - A line drawn between the **highest points of the iliac crests** on both sides typically intersects the L4 vertebral body or the L4-L5 intervertebral space. - This anatomical landmark provides a **safe entry point** for lumbar puncture, avoiding the spinal cord which usually ends at L1-L2. *The lowest pair of ribs bilaterally* - The lowest pair of ribs (12th ribs) corresponds to the **twelfth thoracic vertebra (T12)**, which is much higher than the desired lumbar puncture site. - Using this landmark would place the needle at a level where the **spinal cord is still present**, posing a significant risk of injury. *The inferior angles of the scapulae* - The inferior angle of the scapula typically corresponds to the **seventh thoracic vertebra (T7)**. - This landmark is also too superior for a safe lumbar puncture and does not accurately localize the lumbar spine. *The posterior superior iliac spines* - The posterior superior iliac spines (PSIS) are located at the level of the **S2 vertebra**, which is too far inferior for a standard lumbar puncture at L4-L5. - While they are important pelvic landmarks, they are not used for determining the L4 vertebral spine in this context.
Question 3: 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.
Question 4: A patient comes to ED with fever and headache. On examination he has neck stiffness. CSF analysis was done: Glucose 55 mg/dl (normal 50-80), Protein 0.50 g/L (normal 0.18-0.45), ICT 35 cmH2O (normal 5-20), WBC 25 (predominantly lymphocytes). Most likely diagnosis is:
- A. Cryptococcus
- B. TB
- C. N. Gonorrhea
- D. Coxsackie (Correct Answer)
Explanation: ***Coxsackie*** - The CSF analysis shows **normal glucose**, **mildly elevated protein**, **moderately elevated opening pressure**, and a **淋巴细胞主导** pleocytosis, which are characteristic findings in **viral meningitis**, commonly caused by enteroviruses such as Coxsackie virus [1]. - The combination of **fever, headache, neck stiffness**, and the specific CSF profile strongly points towards a viral etiology [1]. *Cryptococcus* - While fungal meningitis can present with similar symptoms and lymphocyte-dominant pleocytosis, it typically causes **markedly low CSF glucose** and **higher protein levels** than observed here. - Diagnosis usually requires specific tests like **India ink stain** or **cryptococcal antigen detection**, which are not indicated by these CSF findings. *TB* - Tuberculous meningitis usually presents with **very low CSF glucose** (often <40 mg/dl), **markedly elevated protein** (>1 g/L), and predominantly **lymphocytic pleocytosis**, often with a very slow onset [2]. - The CSF profile in this case, particularly the normal glucose, makes TB less likely [2]. *N. Gonorrhea* - *Neisseria gonorrhoeae* can cause **meningitis**, but it is generally a rare presentation and usually results in **neutrophilic pleocytosis** in the CSF, similar to other bacterial meningitides. - The **lymphocytic predominance** in this patient's CSF makes *N. gonorrhoeae* an unlikely cause.
Question 5: Xanthochromia of CSF is seen in all except:
- A. Bloody tap (Correct Answer)
- B. Increased proteins
- C. Carotene
- D. Subarachnoid hemorrhage
Explanation: ***Bloody tap*** - A bloody tap refers to the presence of blood from a **traumatic lumbar puncture**, which introduces fresh blood into the CSF. - This fresh blood would **not have had sufficient time to lyse** and release hemoglobin or oxyhemoglobin to cause xanthochromia. - Xanthochromia typically develops **2-12 hours after hemorrhage** as RBCs lyse and hemoglobin breaks down into bilirubin. *Subarachnoid hemorrhage* - **Subarachnoid hemorrhage (SAH)** is the **classic cause of xanthochromia**. - Following SAH, RBCs in the CSF undergo lysis, releasing **oxyhemoglobin** (peaks at 12-36 hours) and later **bilirubin** (peaks at 2-4 days). - Xanthochromia is detectable by **spectrophotometry** and helps distinguish SAH from traumatic tap. *Increased proteins* - **Elevated protein levels** (>150 mg/dL) in the CSF can cause yellowish discoloration. [1] - Seen in conditions like **Guillain-Barré syndrome** (albuminocytologic dissociation), **Froin's syndrome**, or tumors causing CSF obstruction. - The yellow color is due to protein concentration and binding properties. *Carotene* - **Severe carotenemia** (hypercarotenemia) from excessive intake of carotene-rich foods can rarely cause xanthochromia. - Carotene is a **lipophilic pigment** that can cross into CSF and impart a yellow color. - This is an uncommon but documented cause. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1275-1276.
Question 6: Two or more oligoclonal bands in cerebrospinal fluid are most often positive in-
- A. Acute bacterial meningitis
- B. Multiple sclerosis (Correct Answer)
- C. Subarachnoid hemorrhage
- D. Polyneuropathy
Explanation: Multiple sclerosis - The presence of two or more oligoclonal bands (OCBs) in the cerebrospinal fluid (CSF) is a hallmark finding in multiple sclerosis (MS), indicating intrathecal immunoglobulin synthesis [1]. - OCBs are found in over 90% of MS patients, reflecting a chronic inflammatory process within the central nervous system [1]. Acute bacterial meningitis - CSF analysis in acute bacterial meningitis typically shows elevated white blood cell count (neutrophils), decreased glucose, and elevated protein, but not characteristic OCBs [2]. - While there may be a generalized immune response, it does not typically produce the specific, persistent OCB pattern seen in MS. Subarachnoid hemorrhage - CSF findings in subarachnoid hemorrhage are characterized by xanthochromia (yellow discoloration due to bilirubin), red blood cells, and elevated protein, but OCBs are not a diagnostic feature [2]. - OCBs are related to intrathecal immunoglobulin production, not the breakdown products of blood. Polyneuropathy - Polyneuropathies, such as Guillain-Barré syndrome, are characterized by albuminocytological dissociation (elevated protein with normal cell count) in CSF, or other findings depending on the specific cause. - While some inflammatory neuropathies can have CSF abnormalities, they do not typically present with the same diagnostic pattern of OCBs as observed in MS.
Question 7: Which of the following does not require a lumbar puncture in children?
- A. HL (Correct Answer)
- B. AML
- C. NHL
- D. ALL
Explanation: ***HL*** - While central nervous system (CNS) involvement is possible in Hodgkin lymphoma (HL), it is **rare** and does not routinely warrant a **lumbar puncture** for initial staging or surveillance in asymptomatic children. - HL primarily affects **lymph nodes** and the **spleen**, with CNS spread being an uncommon complication that typically presents with specific neurological symptoms. *AML* - **Acute myeloid leukemia (AML)** has a significant risk of **CNS involvement**, requiring a **lumbar puncture** for diagnostic staging and administration of intrathecal chemotherapy. - CNS prophylaxis and treatment are crucial in AML to prevent and manage **leptomeningeal disease**. *NHL* - **Non-Hodgkin lymphoma (NHL)**, particularly aggressive subtypes like Burkitt lymphoma or lymphoblastic lymphoma, has a **high propensity for CNS spread**. - A **lumbar puncture** is essential for staging to detect CNS involvement and guide the need for intrathecal chemotherapy or radiation. *ALL* - **Acute lymphoblastic leukemia (ALL)** carries a well-documented **high risk of CNS infiltration**, necessitating routine **lumbar punctures** at diagnosis for CNS staging and throughout treatment for intrathecal chemotherapy. - CNS prophylaxis is a cornerstone of ALL treatment to prevent **leptomeningeal relapse**.
Question 8: Which is the best fluid for postmortem investigation?
- A. CSF
- B. Serum
- C. Synovial fluid
- D. Vitreous (Correct Answer)
Explanation: ***Vitreous humor*** is the **best fluid for postmortem investigation** due to its relative isolation and slow decomposition compared to other body fluids. It offers a **stable matrix** for analyzing electrolytes (especially potassium for estimating postmortem interval), drugs, and alcohol, providing a clearer picture of antemortem levels. *CSF (Cerebrospinal fluid)* is more susceptible to rapid postmortem changes and bacterial contamination. While useful in some cases, its instability makes it less reliable for general postmortem analysis compared to vitreous humor. *Serum* undergoes rapid and significant degradation after death, leading to hemolysis and the release of cellular contents. This makes postmortem serum analysis challenging as its composition quickly deviates from antemortem levels, potentially causing misleading results. *Synovial fluid* is found in joints and is prone to putrefaction and contamination soon after death. Its limited volume and rapid decomposition make it less suitable for comprehensive postmortem analysis.
Question 9: What is the normal intracranial pressure in a child (in mmH2O)?
- A. 30-70 mm of H2O
- B. 50-80 mm of H2O (Correct Answer)
- C. 50-150 mm of H2O
- D. 100-150 mm of H2O
Explanation: ***50-80 mm of H2O*** - This range represents the normal **intracranial pressure (ICP)** values for children. - While exact reference ranges can vary slightly between sources, this option falls within the generally accepted normal limits for a child. *30-70 mm of H2O* - This range is typically considered normal for **infants**, who have more compliant skulls and lower baseline ICP. - It is often too low for an older child, especially once the **fontanelles** have closed. *50-150 mm of H2O* - The upper end of this range (above 80 mmH2O) would indicate **elevated ICP** in children. - While the lower end is normal, the broadness makes it less precise for normal physiologic ICP. *100-150 mm of H2O* - This range clearly indicates **elevated intracranial pressure** in a child, necessitating immediate clinical evaluation and intervention. - Normal ICP in children is significantly lower than these values.
Question 10: Diagnosis of Gout is confirmed by which test?
- A. X- ray changes
- B. Urine uric acid levels
- C. Synovial fluid analysis (Correct Answer)
- D. Serum Uric acid level
Explanation: ***Synovial fluid analysis*** - Diagnosis of gout is definitively confirmed by the presence of **negatively birefringent, needle-shaped urate crystals** within neutrophils in the synovial fluid [1]. - This direct visualization of crystals confirms the diagnosis and differentiates gout from other forms of arthritis [1]. *X-ray changes* - While X-rays can show characteristic changes in chronic gout, such as **punched-out erosions with overhanging edges** (rat-bite erosions), these are not diagnostic of acute gout and may appear late in the disease course. - X-ray findings are less specific and do not confirm the presence of urate crystals. *Urine uric acid levels* - Urine uric acid levels help to distinguish between **overproducers and underexcreters** of uric acid, which can guide long-term management strategies [1]. - However, they do not directly confirm the diagnosis of an acute gouty attack. *Serum Uric acid level* - Elevated serum uric acid (hyperuricemia) is a prerequisite for gout, but many individuals with hyperuricemia never develop gout [1]. - Therefore, a **high serum uric acid level alone is not sufficient** to diagnose gout, especially during an acute attack when levels can sometimes be normal [1].
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