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LUMBAR PUNCTURE AND SPINAL FLUID

John E. Greenlee, M.D.

Objectives:

1. Know indications and contraindications for L.P.

2. Know procedure for performing the L.P.

3. Know abnormalities in CSF with bacterial, viral, tuberculosis and fungal meningitis.

Introduction:

Examination of the cerebrospinal fluid (CSF) is an essential part of the evaluation of a number of conditions. With skill, lumbar puncture can be made easy in most cases. The CSF obtained can provide crucial data, but accuracy of data depends in part on how carefully the study was performed and carried out. T here are also patients in whom lumbar puncture should not be done and can cause death. This lecture will review some basic aspects about spinal fluid, then talk about how one does the lumbar puncture, and then discuss the information which one can obtain from CSF analysis. The teaching questions at the end should help you gain better understanding of CSF changes in various conditions.

I. Basic facts about the cerebrospinal fluid

A.     CSF is contained in the space between the arachnoid and the pia, involving the entire of the cranium and spinal canal to S1.

B.     CSF is produced by choroid plexuses within the cerebral ventricles. CSF circulates first through the ventricles, then through the subarachnoid space around brain and spinal cord. CSF is reabsorbed by arachnoid granulations. Most of these are located along venous sinuses, especially the superior sagittal sinus. Others are located throughout the neuraxis.

C.     The choroid plexi are specialized structures and produce what is essentially an ultrafiltrate of plasma, with very different cell count and chemistries. For the most part, however, you will only need to concern yourself with a few parameters

How many cells?

What kind of cells?

How high is the protein?

What is the glucose level compared to blood glucose?

Are bacteria or other agents present?

(In some but not all patients) are immunoglobulins present? Are species of immunoglobulins present which are absent from blood? (oligoclonal bands)

D.     The spinal cord ends at about T12. Below this are nerve roots – the cauda equina. Lumbar puncture can be safely done below L1-2, since the needle has no risk of injuring the spinal cord.

E.      The total volume of the CSF space is about 125 ml. CSF is produced rapidly enough that this volume turns over completely every 7 hours.

II. Indications for Lumbar Puncture

A.     Suspected involvement of the meninges by infection or malignancy

B.      Documentation of subarachnoid hemorrhage

C.     Diagnosis (or exclusion) of infectious or inflammatory conditions involving brain or spinal cord excluding space-occupying infections

D.     Documentation or treatment of intracranial hypertension in pseudotumor cerebri

III. Contraindications to lumbar puncture:

A.     Intracranial mass lesion, especially if rapidly progressive

1.      Mortality after lumbar puncture in the setting of brain abscess = 20%. Death in this setting does not usually occur during the lumbar puncture but rather a few hours later, as CSF continues to leak out through the hole made in the arachnoid by the LP.

2.      Similar -if not greater - risk exists with LP in the setting of subdural empyema or large epidural abscess

3.      Advanced meningitis with significant cerebral edema also behaves as a mass lesion. In this setting treat first, control intracranial pressure, and then do LP. Note that you cannot predict the likelihood of brain herniation in the setting by CT or MRI

B.     Anticoagulation or bleeding diathesis

C.     Infection at the site of suspected lumbar puncture

IV. Performing the Lumbar Puncture

A.     Key Points to a hassle-free LP

1.      Decide what tests you need in advance

2.      Draw simultaneous blood sugar before doing the LP

3.      When to do the LP: immediately in case of emergency. Otherwise, time the LP to give the labs the best opportunity to give you useful data (i.e. it doesn't make sense to do an LP late Friday P.M. for cytology if the cytology lab is closed from 4:00 P.M. Friday to 8:00 A.M. Monday)

4.      Get comfortable

5.      Position the patient properly.

·        Have the patient's back absolutely vertical

·        Use help to get the patient to curl up

6.      Choose a good interspace: L3-4 or L4-5. Not L5-S1

7.      Hold the needle properly. Needle should be perpendicular to the back and aimed straight inward or angled very slightly upwards

8.      Go deep enough

9.      Use the flexible connector on the LP tray - especially in an agitated or moving patient

B.      Information to obtain from the LP

1.      Pressure: Under 150 mm CSF is normal. 150-180 is a gray area. Over 180 mm CSF is abnormal.

2.      Color: Should be clear, colorless

·        High protein levels, cells, or bacteria may cause turbidity

·        Blood causes xanthochromia. So can very high protein levels and so can leptomeningeal seeding by melanoma.

·        Remember: if the patient is yellow, the CSF is likely to be yellow, too.

·        Is blood present? If so, plan to send tubes 2 and 4 for cell count unless the CSF obviously and rapidly clears. The cell count, to be worth anything, must be performed promptly and done by the same person.

3.      What to send:

·        Simultaneous blood sugar: draw before you begin the LP

·        Tube 1: Culture and sensitivity: about 5 ml of CSF

·        Tube 2: Glucose and Protein: About 1 ml.

à        Normal glucose: about 2/3 of blood sugar. Below 50% of blood glucose is abnormally low

à        Protein: <40. Protein levels may rise in old age. Blood raises protein concentration by 1 mg/dl / 1000 RBCs.

·        Tube 3: Cell count (<5 cells, 0 PMNs). The cell count should be done immediately: The longer the delay, the less accurate the count will be.

à        Cells not only settle, they adsorb to the walls of the tube, and not all of them come off with agitation

à        Cells may lyse in grossly purulent CSF

·        Tubes 4-?: Specialized tests: oligoclonal bands (requires simultaneous red top tube) cryptococcal antigen, VDRL, cytology

·        Cultures for TBC, fungi: plan to culture from at least 20 ml of CSF (it is sometimes helpful to use this large a volume for cytology, also)

·        PCR: increasingly useful in CNS infections

à        Tuberculous meningitis

à        Herpes simplex encephalitis

à        Herpes zoster encephalitis

à        Meningoencephalitis due to EBV

à        Enterovirus encephalitis

à        Meningoencephalitis due to Mycoplasma

à        JC virus (PML in AIDS patients)

à        Beginning to be used in bacterial meningitis

4.      Record your data. Use flow sheet where there are multiple CSF examinations

C.     Alternate routes of obtaining CSF: high cervical or cisternal puncture (under radiological control): used in chronic meningitis if lumbar CSF unrevealing

V. Complications of Lumbar Puncture

A.     Most common: post lumbar puncture headache

B.      Most dangerous: brain herniation

·        Usually does not occur during the lumbar puncture itself but rather several hours later, as CSF continues to leak through the defect made by the needle

C.     Other:

1. Cortical blindness

2. Cervical spinal cord infarction

3. Spinal hematoma with cord compression

4. Introduction of infection into the subarachnoid space

5. Development of intraspinal epidermoid tumor (rare)

VI. Significance of abnormal CSF findings:

A. Meningitis

	Bacterial Meningitis	Viral Meningitis	Tuberculous Meningitis	Fungal Meningitis
Protein	Elevated	Mildly elevated	Elevated (extreme)1	Elevated
Glucose	<50% blood glucose	Normal2	<50% blood glucose	<50% blood glucose
Cells	Poly's	Lymphs3	Lymphs +poly's	Lymphs
Other	Gram stain4 Culture	PCR (Viral Culture)	AFB Stain5 Culture (20 ml CSF) PCR	India Ink Prep Cryptococcal Ag Culture (20 ml CSF) PCR

1. In Tuberculous meningitis, very high levels of protein (approaching 1 g/dl) may cause formation of a proteinaceous clot called a pellicle. This was a classical finding in untreated TB meningitis but is now rare.

2. CSF glucose may occasionally be depressed in meningitis due to mumps, lymphocytic choriomeningitis virus, or herpes zoster

3. CSF during the first 24 hours of viral meningitis may contain a mixture of lymphocytes and polymorphonuclear leukocytes. In these cases, in contrast to bacterial meningitis, CSF glucose is normal and follow-up LP in 24 hours will almost always show lymphocytes only.

4. Positive Gram's stain requires about 105 colony-forming units (CFU) /ml of CSF. About 25% of Gram's stains will be positive if CSF contains 103 CFU/m. prior antibiotic treatment will reduce this 20%

5. The AFB stain, in experienced hands, will be positive in approximately 30% of cases; in most hospital laboratories 0-10% of cases. Newer techniques (e.g. FA methods) increase sensitivity. The AFB stain has been largely supplanted by PCR

6. Remember: Immunosuppressed patients (e.g. with HIV infection) may show a blunted CSF inflammatory response.

B. Encephalitis: Classical findings vary widely. CSF is occasionally normal. More often it contains increased lymphocytes, elevated protein, normal glucose. Occasionally, PMNs may be present and rarely glucose may be low (esp. in mumps, LCM, herpes zoster, occasionally Lyme disease).

C. Leptomeningeal spread of cancer: CSF may be normal. Any CSF change - in cells, glucose, or protein in a patient with cancer should raise this question.

D. CSF inflammatory conditions: CSF may be normal by routine tests. In some cases lymphocytosis, elevated protein may be present. High protein levels in Guillain-Barre syndrome.

E. Oligoclonal bands: Positive in multiple sclerosis, often positive in paraneoplastic syndromes. Occasionally positive in chronic CNS infections. In rare cases may be positive after strokes, head trauma, tumors, etc.

F. Isolated abnormalities

· 1 or 2 PMNs on CSF cell count: worrisome, since they shouldn't be there. Acceptable if there is absolutely nothing on exam to suggest pathology - but you should worry

· Elevated protein: is the least specific - and often the least useful - of all CSF abnormalities. For the most part, don't worry about minor elevations. Major elevations should be worked up.

· Depressed glucose <50% of blood glucose is of concern, and below 20% of blood glucose of major concern. Something is almost certainly going on to disrupt glucose transport across the blood-brain barrier, and that "something" is usually meningeal involvement by infection or tumor. Remember that in meningitis, especially tuberculous meningitis, the CSF glucose may fall before other CSF changes become evident.

HOW TO RECORD THE LUMBAR PUNCTURE

Indication: State why you are doing the lumbar puncture (e.g. suspected meningitis)

Informed consent obtained. Patient placed in (right or left) decubitus position, prepped and draped. Under __% xylocaine local infiltration, spinal canal entered without (or with slight, moderate or marked) difficulty at L__.

Opening Pressure:_____

Closing Pressure: _____

Fluid: (Describe appearance)

Samples sent for:

Tube	Sent for	Result
1
2
3
4
5

Patient tolerated procedure without difficulty

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REFERENCES

1. Greenlee JE. Cerebrospinal fluid in central nervous system infections. In: Scheld WM, Whitley RJ, Durack DT, eds. Infections of the central nervous system. 2nd ed. Philadelphia: Lippincott-Raven Publishers; 1997:899-922.

2. Fishman RA. The Cerebrospinal Fluid. 2nd Edition. Philadelphia. W.B. Saunders, 1992.

3. Kaneko K, Onodera O, Miyatake T, Tsuji S. Rapid diagnosis of tuberculous meningitis by polymerase chain reaction (PCR). Neurology 1990;40:1617-1618.

4. Steele RW, Marmer DJ, O'Brien MD, Tyson ST, Steele CR. Leukocyte survival in cerebrospinal fluid. J Clin Microbiol 1986;23:965-966.

5. Shantha TR, Bisese J. Subdural blood patch for spinal headache. N Engl J Med 1991;325:1252-1253.

6. Berenguer J, Moreno S, Laguna F, et al. Tuberculous meningitis in patients infected with the human immunodeficiency virus. N Engl J Med 1992;326:668-672.

7. Fraser JL. Persistent lumbar aglycorrhachia of unknown cause. Neurology 1991;41:1323-1324.

8. Rogers LR, Duchesnau PM, Nunez C, et al. Comparison of cisternal and lumbar CSF examination in leptomeningeal metastasis. Neurology 1992;42:1239-1241.

9. Durand ML, Calderwood SB, Weber DJ, et al. Acute bacterial meningitis in adults. A review of 493 episodes. N Engl J Med 1993;328:21-28.

10. Aslanzadeh J, Osmon DR, Wilhelm MP, Espy MJ, Smith TF. A prospective study of the polymerase chain reaction for detection of herpes simplex virus in cerebrospinal fluid submitted to the clinical virology laboratory. Mol Cell Probes 1992;6:367-373.

11. Bartleson JD, Swanson JW, Whisnant JP. A migrainous syndrome with cerebrospinal fluid pleocytosis. Neurology 1981;31:1257-1262.

12. Read SJ, Jeffery KJ, Bangham CR. Aseptic meningitis and encephalitis: the role of PCR in the diagnostic laboratory. J Clin Microbiol. 1997;35:691-6.

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