csf fcps exam high yield points
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Finding Sources
I now have comprehensive data from multiple authoritative textbooks. Let me compile the full high-yield FCPS answer.
CSF - High Yield Points for FCPS Exam
1. Normal CSF Values
| Parameter | Normal Value |
|---|---|
| Opening pressure | 70-180 mmH₂O (lateral recumbent position) |
| Appearance | Clear, colorless, "water-like" |
| Total protein | 15-45 mg/dL (lumbar; ventricular < spinal) |
| Glucose | 50-75 mg/dL (or ~60% of serum glucose) |
| WBC count | 0-5/µL (adults); 0-20/µL (neonates) |
| Cell differential | Lymphocytes 30-90%, Monocytes 10-50%, Neutrophils 0-6% |
| Volume | ~150 mL total |
| Production | ~500 mL/day; completely replaced ~4x daily |
Key: CSF is produced primarily by the choroid plexus. Normal CSF has NO neutrophils and NO RBCs. - Quick Compendium of Clinical Pathology, p. 53
2. CSF in Meningitis - The Classic Comparison Table
| Type | Opening Pressure | WBC (/µL) | Glucose (mg/dL) | Protein (mg/dL) | Diagnosis |
|---|---|---|---|---|---|
| Normal | <180 | 0-5 | 50-75 | 15-40 | - |
| Bacterial | ↑↑ | 100-5000, neutrophils | <40 | 100-500 | Gram stain, culture |
| Viral (aseptic) | ↑ | 10-1000, lymphocytes | Normal | 50-100 | PCR (enterovirus, HSV) |
| Tuberculous | ↑↑ | 50-300, lymphocytes | <45 | 50-300 | AFB smear/culture, PCR |
| Cryptococcal | ↑↑↑ | 20-500, lymphocytes | <40 | >45 | India ink, CrAg, fungal culture |
- The Washington Manual of Medical Therapeutics, p. 520; Neuroanatomy through Clinical Cases, p. 186
3. Bacterial Meningitis - Classic CSF Triad (Harrison's)
Four hallmarks - ALL present in >60-90% of cases:
- PMN leukocytosis - >100 cells/µL in 90%
- Low glucose - <2.2 mmol/L (<40 mg/dL) in ~60%; CSF/serum ratio <0.4
- High protein - >45 mg/dL in 90%
- Elevated opening pressure - >180 mmH₂O in 90%; >400 mmH₂O in 20%
- CSF cultures positive in >70%; Gram stain positive in >60%
- CSF/serum glucose ratio <0.4 = highly suggestive of bacterial meningitis (also seen in fungal, TB, carcinomatous meningitis)
- A CSF glucose of zero can occur in bacterial meningitis
- Harrison's Principles of Internal Medicine 22E, p. 1164
4. Viral (Aseptic) Meningitis - Key Points
- Lymphocytic pleocytosis (50-1000/µL)
- Glucose normal
- Protein mildly elevated, usually <150 mg/dL
- Important trap: In early enteroviral meningitis (first 24-48h), neutrophils can predominate in ~50% of patients - then shifts to lymphocytes
- Decreased glucose is classically seen with HSV, mumps, and LCM virus (rare exceptions to normal glucose rule)
- PCR sensitivity 85-100%, specificity 95-100% - gold standard for viral meningitis
- Goldman-Cecil Medicine; Neuroanatomy through Clinical Cases
5. Subarachnoid Hemorrhage (SAH) - CSF Findings
Xanthochromia = pink or yellow tinge of CSF after centrifugation
- Pink xanthochromia = free hemoglobin (acute/recent bleed)
- Yellow xanthochromia = bilirubin from hemoglobin metabolism
Time course of xanthochromia:
- Begins: ~12 hours after bleed
- Peaks: 72 hours
- Disappears: 2-4 weeks
Distinguishing SAH from traumatic tap:
| Feature | SAH | Traumatic Tap |
|---|---|---|
| Xanthochromia | Present | Absent |
| Serial tubes (1→4) | Uniformly bloody | Clears progressively |
| Erythrophagocytosis + hemosiderin macrophages | Present | Absent |
Correction for traumatic tap: Add 1 WBC per ~700 RBCs (if blood counts are normal)
Key exam point: If CT head is negative but SAH is still suspected, LP must be done and xanthochromia is the key finding. - Quick Compendium of Clinical Pathology, p. 53
6. Specific Neurological Conditions
Guillain-Barre Syndrome (GBS)
- Classic finding: Albuminocytologic dissociation - markedly elevated protein WITH NORMAL or near-normal cell count (<10 cells/µL)
- Protein typically >45 mg/dL, can be very high
- Normal glucose
- This pattern = the pathognomonic CSF finding for GBS (and also CIDP)
- Neuroanatomy through Clinical Cases; Adams & Victor's Principles of Neurology
Multiple Sclerosis (MS)
- Oligoclonal bands (OCBs) in CSF gamma region (NOT in serum) = intrathecal IgG synthesis
- Present in up to 95% of MS cases (Tietz)
- IgG index = (CSF IgG/Serum IgG) ÷ (CSF albumin/Serum albumin) - elevated in MS
- OCB patterns:
- Type 1: No bands in CSF or serum - normal
- Type 2: OCBs in CSF only, NOT serum = intrathecal IgG synthesis (classic MS)
- Type 3: OCBs in CSF + other bands in serum
- Mild lymphocytic pleocytosis may be present
- Quick Compendium of Clinical Pathology; Henry's Clinical Diagnosis
Herpes Encephalitis (HSV)
- Lymphocytic pleocytosis (0-500/µL)
- RBCs or xanthochromia may be present (hemorrhagic necrosis of temporal lobes)
- Glucose: normal OR reduced
- Protein elevated
- PCR for HSV DNA = gold standard
- Neuroanatomy through Clinical Cases
Neurosyphilis
- Lymphocytic pleocytosis
- Elevated protein
- VDRL on CSF = most specific test (but low sensitivity)
- FTA-ABS on CSF = most sensitive
Cryptococcal Meningitis
- Markedly elevated pressure (can be very high)
- India ink - visualizes encapsulated yeast
- Cryptococcal antigen (CrAg) - most sensitive (close to 100%)
- Low glucose, elevated protein
7. CSF - Other High-Yield Facts
| Condition | Key CSF Finding |
|---|---|
| Hepatic encephalopathy | Elevated CSF glutamine |
| CSF leak (rhinorrhea/otorrhea) | β₂-transferrin (most specific); prostaglandin D synthase |
| Carcinomatous meningitis | ↑ Protein, ↓ glucose, lymphocytes; cytology positive |
| Alzheimer's disease | ↓ Aβ42, ↑ tau, ↑ phospho-tau |
| Pseudotumor cerebri (IIH) | Very high opening pressure; otherwise NORMAL CSF |
| Spinal block (Froin's syndrome) | Very high protein, yellow color, clots spontaneously |
| Neurosarcoidosis | Lymphocytic pleocytosis, elevated protein, low glucose |
8. Lumbar Puncture - Key Exam Points
- Safe without CT first in: immunocompetent, no focal neuro deficits, no papilledema, normal level of consciousness, no recent head trauma
- Get CT before LP if: focal deficits, papilledema, reduced consciousness, seizures - risk of herniation
- Do NOT delay antibiotics for CT/LP if bacterial meningitis suspected
- Dexamethasone should ideally start 20 minutes before (or concurrent with) first antibiotic dose
- LP level: L3-L4 or L4-L5 interspace (below spinal cord termination at L1-L2)
- Opening pressure measured with patient in lateral decubent position
- More than 90% of bacterial meningitis patients have CSF opening pressure >180 mmH₂O; 20% have >400 mmH₂O
- Harrison's Principles of Internal Medicine 22E
9. Empirical Antibiotic Treatment by Age Group
| Age Group | Empirical Regimen |
|---|---|
| Preterm - <1 month | Ampicillin + cefotaxime |
| 1-3 months | Ampicillin + cefotaxime/ceftriaxone |
| Children >3 months, adults <55 | Cefotaxime/ceftriaxone + vancomycin |
| Adults >55, alcoholism, debilitating illness | Ampicillin + ceftriaxone + vancomycin |
| Nosocomial/post-neurosurgery | Ampicillin + ceftazidime/meropenem + vancomycin |
(Add ampicillin to cover Listeria in elderly and immunocompromised)
10. Quick Memory Pegs for FCPS
- "Bacterial = Bad 4s" → Neutrophils, ↓Glucose (<40), ↑Protein (>100), ↑Pressure
- Viral = "Normal glucose, lymphocytes" - but watch out for early neutrophil shift
- TB/Crypto = "Low glucose + lymphocytes" - similar to each other; use AFB/CrAg to differentiate
- GBS = "Protein up, cells down" (albuminocytologic dissociation)
- MS = "Oligoclonal bands in CSF not serum"
- SAH = xanthochromia - starts at 12h, peaks 72h, gone by 4 weeks
- CSF glucose = 60% serum glucose (range 40-80%)
- Traumatic tap correction: 1 WBC per 700 RBCs
- CSF/serum glucose <0.4 = highly suggestive of bacterial meningitis
This is a shared conversation. Sign in to Orris to start your own chat.