Neuroscience Clerkship

 
 

Lumbar Puncture
Lumbar puncture (LP), through the analysis of cerebrospinal fluid (CSF) aids in the diagnose of many important and potentially life-threatening conditions. Two conditions which require an urgent lumbar puncture to rule out include meningitis and subarachnoid hemorrhage.

TECHNIQUE

1)Place the patient in lateral recumbent position with the neck, hips and knees in the flexed position.

2) Disinfect overlying skin

3) Pass a 20 gauge needle into a lower lumbar intervertebral space (in adults, the spinal cord ends at the level of the L1 vertebral body; any level below can be performed safely without risk of spinal cord injury. A line drawn between the pelvic crests typically intersects the vertebral column at the L3-4 level). Flat surface of the bevel needle should be positioned to face upwards to allow the needle to separate rather than cut the dura.
Spinal Needle and Stylette

4) Enter the subarachnoid space

(Figure above from JAMA. 2002; 288: 2070)

5) Attach a manometer and measure the opening pressure (normal OP is 60 to 200 mm H20) 

6) Collect CSF in serial sterile tubes

7) Samples are always (routinely) sent for cell count and differential (tubes 1 and 4), protein and glucose, and culture. Additional studies can be performed depending on the differential diagnosis.
DIAGNOSTIC INDICATIONS

 

     Most Important:

Meningitis (especially bacterial)

Encephalitis (especially herpes simplex)

Subarachnoid hemorrhage


     May Be Useful:

Carcinomatous/lymphomatous meningitis

Multiple sclerosis

Guillain-Barré syndrome

Neurosarcoidosis

Pseudotumor cerebri

Normal pressure hydrocephalus

CNS vasculitis

CNS syphilis
 

THERAPEUTIC INDICATIONS

Intrathecal chemotherapy

Withdrawal of CSF for pseudotumor cerebri

Spinal anesthesia

Injection of contrast media for myelography or cisternography

CONTRAINDICATIONS

     Absolute Contraindications

Severe coagulopathy or thrombocytopenia

Infection at the puncture site (e.g., an LP cannot be performed if the needle needs to be passed through an infected area of skin)

Compartmentalized increased intracranial pressure
Explanation of Compartmental Increased Intracranial Pressure: LP is contraindicated in cases where there is compartmentalized increased intracranial pressure. If there is a pressure gradient either between lumbar space and the posterior fossa; or between the lumbar space and the supratentorial compartment, withdrawal of CSF can lower the pressure in the lumbar space, increase the pressure gradient, and potentially lead to herniation and death (C). In normals (A), there is no pressure gradient between the brain and lumbar space (in the recumbent position). Increased intracranial pressure is not a contraindication to a LP if the increased pressure is uniform throughout the neuraxis (B). For example, in pseudotumor cerebri (a.k.a., idiopathic intracranial hypertension), the CSF pressure is often extremely high; however, LP carries no risk as there is no pressure gradient between compartments. Indeed, in this condition, LP is often performed as a therapeutic measure to remove CSF and decrease the pressure. Compartmentalized intracranial pressure is suggested clinically by the presence of any sign or symptom of increased intracranial pressure (e.g., papilledema) and the presence of any focal neurologic sign. For a practical perspective, routine brain CT or MRI imaging is indicated and is considered the standard of care for all patients before LP is performed. Essentially, compartmentalized increased intracranial pressure results from mass lesions and mass effect; both easily seen on routine brain imaging.
 
     Relative Contraindications


Any sign or symptom suggestive of increased intracranial pressure (e.g., papilledema)

Any focal neurologic sign

POTENTIAL COMPLICATIONS

     Infection

Meningitis caused by LP in a bacteremic patient

Meningitis caused by contaminated instruments/solutions or poor technique

     Bleeding

Potential risk of epidural, subdural hematoma and cauda equina syndrome, especially in anticoagulated or thrombocytopenic patients

     Herniation and Death

Only in the setting of a mass lesion and compartmentalized increased intracranial pressure

     Transient Minor Neurologic Symptoms

Radicular pain or paresthesias

     Post-LP headache (low pressure headache)

10-30% of patients

Caused by leakage of CSF from dura and traction on pain sensitive structures

Common associated symptoms: nausea, vomiting, dizziness, tinnitus and visual changes

LIMITATIONS
 

Many CSF abnormalities are non-specific, especially elevation of protein.

In some cases of encephalitis (where the process has not spread to the meninges), the study may be normal. This may also occur in early brain abscess and other parameningeal infections (e.g., subdural empyema, etc).

Traumatic taps are common, especially if multiple passes of the spinal needle are required. Thus, differentiating a traumatic LP from true subarachnoid hemorrhage can be problematic. The following can be helpful:


• In traumatic LP, the number of RBCs typically decreases between the first and last tubes.

• In traumatic LP, the ratio of RBCs/WBCs is similar to whole blood (typically between 500:1 - 1000:1).

• Likewise, for every 1000 RBCs from a traumatic tap, the protein elevates 1 mg/dl.

• Xanthochromia favors subarachnoid hemorrhage.

• CSF cytology is often negative in true carcinomatous or lymphomatous meningitis - multiple repeats taps are often required.

LP has a high sensitivity for bacterial and fungal infections, but only moderate sensitivity and specificity for diagnosing viral encephalitis, tuberculous and spirochetal CNS infections.