Lumbar puncture

Lumbar puncture (LP), also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing. The main reason for a lumbar puncture is to help diagnose diseases of the central nervous system, including the brain and spine. Examples of these conditions include meningitis and subarachnoid hemorrhage. It may also be used therapeutically in some conditions. Increased intracranial pressure (pressure in the skull) is a contraindication, due to risk of brain matter being compressed and pushed toward the spine. Sometimes, lumbar punctures cannot be performed safely (for example due to a severe bleeding tendency). It is regarded as a safe procedure, but post-dural-puncture headache is a common side effect if a small atraumatic needle is not used.

The procedure is typically performed under local anesthesia using a sterile technique. A hypodermic needle is used to access the subarachnoid space and collect fluid. Fluid may be sent for biochemical, microbiological, and cytological analysis. Using ultrasound to landmark may increase success.

Lumbar punctures were first introduced in 1891 by the German physician Heinrich Quincke.

Medical uses

The reason for a lumbar puncture may be to make a diagnosis or to treat a disease, as outlined below. inflammatory, since there is no other reliable tool with which meningitis, a life-threatening but highly treatable condition, can be excluded. A lumbar puncture can also be used to detect whether someone has Stage 1 or Stage 2 Trypanosoma brucei. Young infants commonly require lumbar puncture as a part of the routine workup for fever without a source. This is due to higher rates of meningitis than in older persons. Infants also do not reliably show classic symptoms of meningeal irritation (meningismus) like neck stiffness and headache the way adults do.

Treatment

Lumbar punctures may also be done to inject medications into the cerebrospinal fluid ("intrathecally"), particularly for spinal anesthesia or chemotherapy.

Serial lumbar punctures may be useful in temporary treatment of idiopathic intracranial hypertension (IIH). This disease is characterized by increased pressure of CSF which may cause headache and permanent loss of vision. While mainstays of treatment are medication, in some cases lumbar puncture performed multiple times may improve symptoms. It is not recommended as a staple of treatment due to discomfort and risk of the procedure, and the short duration of its efficacy.

Additionally, some people with normal pressure hydrocephalus (characterized by urinary incontinence, a changed ability to walk properly, and dementia) receive some relief of symptoms after removal of CSF.

Contraindications

Lumbar puncture should not be performed in the following situations:

Idiopathic (unidentified cause) increased intracranial pressure (ICP)
Rationale: lumbar puncture in the presence of raised ICP may cause uncal herniation
Exception: therapeutic use of lumbar puncture to reduce ICP, but only if obstruction (for example in the third ventricle of the brain) has been ruled out
Precaution
CT brain, especially in the following situations
Age >65
Reduced GCS
Recent history of seizure
Focal neurological signs
Abnormal respiratory pattern
Hypertension with bradycardia and deteriorating consciousness
Ophthalmoscopy for papilledema
Bleeding diathesis (relative)
Coagulopathy
Decreased platelet count (<50 billion/L)
Infections
Skin infection at puncture site
Vertebral deformities (scoliosis or kyphosis), in hands of an inexperienced physician.

Adverse effects

Headache

Post-dural-puncture headache with nausea is the most common complication; it often responds to pain medications and infusion of fluids. It was long taught that this complication can be prevented by strict maintenance of a supine posture for two hours after the successful puncture; this has not been borne out in modern studies involving large numbers of people. Doing the procedure with the person on their side might decrease the risk. Intravenous caffeine injection is often quite effective in aborting these spinal headaches. A headache that is persistent despite a long period of bedrest and occurs only when sitting up may be indicative of a CSF leak from the lumbar puncture site. It can be treated by more bedrest, or by an epidural blood patch, where the person's own blood is injected back into the site of leakage to cause a clot to form and seal off the leak.

The risk of headache and need for analgesia and blood patch is much reduced if "atraumatic" needles are used. This does not affect the success rate of the procedure in other ways. Although the cost and difficulty are similar, adoption remains low, at only 16% .

The headaches may be caused by inadvertent puncture of the dura mater.

Other

Contact between the side of the lumbar puncture needle and a spinal nerve root can result in anomalous sensations (paresthesia) in a leg during the procedure; this is harmless and people can be warned about it in advance to minimize their anxiety if it should occur.

Serious complications of a properly performed lumbar puncture are extremely rare.

CSF leaks can result from a lumbar puncture procedure.

Technique

Mechanism

The brain and spinal cord are enveloped by a layer of cerebrospinal fluid, 125–150 mL in total (in adults) which acts as a shock absorber and provides a medium for the transfer of nutrients and waste products. The majority is produced by the choroid plexus in the brain and circulates from there to other areas, before being reabsorbed into the circulation (predominantly by the arachnoid granulations).

The cerebrospinal fluid can be accessed most safely in the lumbar cistern. Below the first or second lumbar vertebrae (L1 or L2) the spinal cord terminates (conus medullaris). Nerves continue down the spine below this, but in a loose bundle of nerve fibers called the cauda equina. There is lower risk with inserting a needle into the spine at the level of the cauda equina because these loose fibers move out of the way of the needle without being damaged. If the procedure is difficult, such as in people with spinal deformities such as scoliosis, it can also be performed under fluoroscopy (under continuous X-ray imaging).

Children

In children, a sitting flexed position was as successful as lying on the side with respect to obtaining non-traumatic CSF, CSF for culture, and cell count. There was a higher success rate in obtaining CSF in the first attempt in infants younger than 12 months in the sitting flexed position.

The spine of an infant at the time of birth differs from the adult spine. The conus medullaris (bottom of the spinal cord) terminates at the level of L1 in adults, but may range in term neonates (newly born babies) from L1–L3 levels. It is important to insert the spinal needle below the conus medullaris at the L3/L4 or L4/L5 interspinous levels. With growth of the spine, the conus typically reaches the adult level (L1) by 2 years of age.

Glass tubes are not recommended, as cells can stick to their walls and lead to underestimation of cell numbers. Samples should be drawn into four sterile tubes in the following order, tube 1 for chemistry tests, tube 2 for microbiology, tube 3 for hematology, and tube 4 for cytology or specialized studies to ensure accurate, and uncontaminated results. where phagocytosed erythrocytes are observed, signifies haemorrhage into the CSF that preceded the lumbar puncture. Therefore, when erythrocytes are detected in the CSF sample, erythrophagocytosis suggests causes other than a traumatic tap, such as intracranial haemorrhage and haemorrhagic herpetic encephalitis. In which case, further investigations are warranted, including imaging and viral culture.

Microbiology

CSF can be sent to the microbiology lab for various types of smears and cultures to diagnose infections.

Gram staining may demonstrate gram positive bacteria in bacterial meningitis.
Microbiological culture is the gold standard for detecting bacterial meningitis. Bacteria, fungi, and viruses can all be cultured by using different techniques.
Polymerase chain reaction (PCR) has been a great advance in the diagnosis of some types of meningitis, such as meningitis from herpesvirus and enterovirus. It has high sensitivity and specificity for many infections of the CNS, is fast, and can be done with small volumes of CSF. Even though testing is expensive, cost analyses of PCR testing in neonatal patients demonstrated savings via reduced cost of hospitalization.
Numerous antibody-mediated tests for CSF are available in some countries: these include rapid tests for antigens of common bacterial pathogens, treponemal titers for the diagnosis of neurosyphilis and Lyme disease, Coccidioides antibody, and others.
The India ink test is still used for detection of meningitis caused by Cryptococcus neoformans, but the cryptococcal antigen (CrAg) test has a higher sensitivity.

Chemistry

Several substances found in cerebrospinal fluid are available for diagnostic measurement.

Glucose is present in the CSF; the level is usually about 60% that in the peripheral circulation. A fingerstick or venipuncture at the time of lumbar puncture may therefore be performed to assess peripheral glucose levels and determine a predicted CSF glucose value. Decreased glucose levels can indicate fungal, tuberculous or pyogenic infections; lymphomas; leukemia spreading to the meninges; meningoencephalitic mumps; or hypoglycemia. A glucose level of less than one third of blood glucose levels in association with low CSF lactate levels is typical in hereditary CSF glucose transporter deficiency also known as De Vivo disease.
Increased glucose levels in the fluid can indicate diabetes, although the 60% rule still applies.
Increased levels of glutamine are often involved with hepatic encephalopathies, Reye's syndrome, hepatic coma, cirrhosis,
Increased levels of lactate can occur the presence of cancer of the CNS, multiple sclerosis, heritable mitochondrial disease, low blood pressure, low serum phosphorus, respiratory alkalosis, idiopathic seizures, traumatic brain injury, cerebral ischemia, brain abscess, hydrocephalus, hypocapnia or bacterial meningitis.
Changes in total protein content of cerebrospinal fluid can result from pathologically increased permeability of the blood-cerebrospinal fluid barrier, obstructions of CSF circulation, meningitis, neurosyphilis, brain abscesses, subarachnoid hemorrhage, polio, collagen disease or Guillain–Barré syndrome, leakage of CSF, increases in intracranial pressure, or hyperthyroidism. Very high levels of protein may indicate tuberculous meningitis or spinal block.
IgG synthetic rate is calculated from measured IgG and total protein levels; it is elevated in immune disorders such as multiple sclerosis, transverse myelitis, and neuromyelitis optica of Devic. Oligoclonal bands may be detected in CSF but not in serum, suggesting intrathecal antibody production.

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! Protein (g/L) The technique for needle lumbar puncture was then introduced by the German physician Heinrich Quincke, who credits Wynter with the earlier discovery; he first reported his experiences at an internal medicine conference in Wiesbaden, Germany, in 1891. He subsequently published a book on the subject.

The lumbar puncture procedure was taken to the United States by Arthur H. Wentworth an assistant professor at the Harvard Medical School, based at Children's Hospital. In 1893 he published a long paper on diagnosing cerebrospinal meningitis by examining spinal fluid. However, he was criticized by antivivisectionists for having obtained spinal fluid from children. He was acquitted, but, nevertheless, he was uninvited from the then forming Johns Hopkins School of Medicine, where he would have been the first professor of pediatrics.

Historically lumbar punctures were also employed in the process of performing a pneumoencephalography, a nowadays obsolete X-ray imaging study of the brain that was performed extensively from the 1920s until the advent of modern non-invasive neuroimaging techniques such as MRI and CT in the 1970s. During this quite painful procedure, CSF was replaced with air or some other gas via the lumbar puncture in order to enhance the appearance of certain areas of the brain on plain radiographs.