Lumbar Puncture

Essentials

• An emergency sample of cerebrospinal fluid is most often taken when acute central nervous system infection or polyradiculitis is suspected, or to exclude subarachnoid haemorrhage (SAH) if cranial CT is normal.
• A non-emergency sample is most often taken when central nervous system inflammation, such as MS, neurosarcoidosis or neuroborreliosis, is suspected, as well as in some cases of suspected malignancy.
• Before the procedure, check the ocular fundi to make sure that the optic discs are clearly defined. This signifies normal intracranial pressure and safe puncture.
• The procedure is performed in the lumbar spine area, where there is no spinal cord but a cavity filled with cerebrospinal fluid. This, as well as the course of events, should be explained to the patient beforehand.
• Careful positioning of the patient in the correct position for the procedure is most important for successful lumbar puncture. Sufficient time should be taken for ensuring the correct position.
• Bed rest after lumbar puncture does not prevent post lumbar puncture headache. Should such headache be prolonged, it should primarily be treated by intravenous caffeine infusion in hospital.

Performance of lumbar puncture

Therapy affecting blood coagulation

• Before the puncture, check complete blood count, prothrombin time and APTT, unless these have been determined within the previous 6 months.
• The platelet count should be > 50 × 10⁹ /l.
• Antithrombotic therapy and lumbar puncture
  • ASA therapy used for secondary prevention does not need to be withheld; if it is used for primary prevention, it is withheld 5-7 days before the puncture.
  • ASA-dipyridamole therapy: last tablet in the previous evening before the puncture and the next tablet in the next morning after the puncture day.
  • Clopidogrel therapy is generally not withheld, unless there are other factors affecting the bleeding tendency.
• Make sure to ask about any anticoagulant therapy before the procedure.
  • Warfarin treatment must be withheld 2-4 days before the puncture.
  • Bridge therapy is not required for low-risk patients (e.g. atrial fibrillation without another cardiac disease)
  • Subcutaneous low-molecular-weight heparin (LMWH) is started as bridge therapy for high-risk patients (e.g. prosthetic mitral valve, severe thrombophilia, recent thrombosis).
    • Enoxaparin 0.5 mg/kg twice daily or dalteparin 50 IU/kg twice daily
    • The last LMWH injection is administered 18-24 hours before the puncture (this also applies to patients who are on LMWH for some other reason).
    • INR is checked on the morning of the day when the puncture is to be performed. INR level < 1.5 is safe.
    • LMWH therapy is resumed no earlier than 6 hours after the lumbar puncture, at the same time with warfarin therapy that is started using earlier home dosage, and continued until INR level has been within therapeutic range for two consecutive days.
  • Before emergency lumbar puncture the effect of warfarin must be reversed.
  • A 1- to 2-day break is recommended for the direct oral anticoagulants (DOACs, 2 days if bleeding risk is pronounced).
    • Resumed not earlier than the following morning.

Carrying out the lumbar puncture

• If the patient has undergone cranial imaging just before the procedure showing normal intracranial pressure, inspection of the ocular fundi is not necessary. If this is not the case, the inspection must always be performed.
• Check the patient's position carefully before the procedure; the aim is to have the back as curved as possible so as to have the intervertebral spaces open. If necessary, ask assisting personnel to keep the patient in the correct position during puncture. The most common error is to have the spine twisted instead of only being bent forward.
• Lumbar puncture can be performed with the patient lying on his/her side or in the sitting position if there is no need to measure the opening pressure. The opening pressure can only be measured with the patient lying on his/her side. If a sample cannot be obtained in one position, an attempt can be made in the other, and this often helps.
• Before scrubbing, palpate the anterior superior iliac spine carefully. Get a clear picture of the spatial configuration of the patient's spine, and identify the best place to insert the needle. Mark the entry site with your nail or with a pen.
• Local anaesthesia removes the sensation of pain on the skin surface and may calm the patient. However, it is not absolutely necessary because two needle pricks will then be needed and local anaesthesia will not remove the sensation of pain in deeper tissues. It is forbidden to anaesthetize the deeper tissue layers as the anaesthetic may enter the spinal cavity.
• If possible, avoid inserting the needle through a scar because a scar will be difficult to penetrate.
• Insertion through a tattoo or other abnormal skin area is not recommended, either.
• The procedure is normally performed in the intervertebral space either above (L3-L4) or below (L4-L5) the level of the anterior superior iliac spine. Direct the needle diagonally upward, taking note of the anatomic "landmarks" you feel (and also any sharp sensation experienced by the patient in a lower limb). When pressure against the needle tip decreases, you have probably reached the right place.
• The procedure may be technically impossible to perform if the patient is very obese, has a history of lumbar fusions or has severe spinal stenosis.
• If the patient is discharged soon after the lumbar puncture, he/she must be informed about possible postpuncture headache and how to treat it.
• The time of the lumbar puncture and its performance need to be documented in the medical records as well as any problems and peripheral blood contamination, as the latter may lead to a suspicion of SAH and consequent unnecessary procedures.

Post lumbar puncture headache

• Occurs in about 10% of patients after sampling and is probably caused by loss of CSF pressure.
• The headache typically occurs only in the upright position and is alleviated by lying down.
• The onset of headache is related more to the amount of fluid leaking into tissues after the puncture than to the amount of fluid withdrawn as a sample. Bed rest after puncture does not prevent headache Posture and Fluids for Preventing Post-Dural Puncture Headache, but strenuous exercise should be avoided for a couple of days.
• Drinking of coffee apparently does not prevent post lumbar puncture headache.

CSF analysis

• Cerebrospinal fluid is normally colourless and clear.
• Turbid, opaque CSF suggests bacterial meningitis.
• Evenly bloody, watery CSF ("lingonberry juice"), reddish/yellow-red after centrifugation (xanthochromia), suggests haemorrhage.
• Yellowish CSF suggests a high protein concentration.
• Fluid that is coagulated and streaked with blood or bloody but later clear and after centrifugation colourless suggests peripheral blood contamination.
• The most common CSF findings are listed in table T1.

Other CSF tests

• IgG index and oligoclonal bands: if MS is suspected Multiple Sclerosis (Ms)
• ACE: if neurosarcoidosis is suspected Sarcoidosis
• Borrelia antibodies and chemokine CXCL 13: in case of suspected borreliosis if serum Borrelia antibodies are increased Lyme Borreliosis (LB) and often if CNS inflammation or infection is suspected
• TPHA and FTA absorption: if neurosyphilis is suspected Syphilis
• Lactate: if infection is suspected; also increased in cerebrovascular disorders, traumas and in connection with convulsions, nowadays rarely used

Exfoliated cells in CSF (microscopic analysis)

• Provides somewhat varying information depending on the laboratory technique used.
• Findings
  • Malignant cells are found in meningeal carcinomatosis (several samples may be required) and in CNS leukaemia, but rarely in connection with primary brain neoplasms.
  • Plasma cells strongly suggest MS; a more common finding in MS is the so-called lymphoid reaction.
  • In connection with CNS infections, independent of the cause, there are three phases in the cellular presentation of CSF:
    • neutrophilic or exudative phase
    • lymphocytic or proliferative phase
    • mononuclear or phagocytic phase.

Emergency examination of CSF