Lumbar Puncture - Diagnostics

Diagnostics

Increased CSF pressure can indicate congestive heart failure, cerebral edema, subarachnoid hemorrhage, hypo-osmolality resulting from hemodialysis, meningeal inflammation, purulent meningitis or tuberculous meningitis, hydrocephalus, or pseudotumor cerebri.

Decreased CSF pressure can indicate complete subarachnoid blockage, leakage of spinal fluid, severe dehydration, hyperosmolality, or circulatory collapse. Significant changes in pressure during the procedure can indicate tumors or spinal blockage resulting in a large pool of CSF, or hydrocephalus associated with large volumes of CSF. Lumbar puncture for the purpose of reducing pressure is performed in some patients with idiopathic intracranial hypertension (also called pseudotumor cerebri.)

The presence of white blood cells in cerebrospinal fluid is called pleocytosis. A small number of monocytes can be normal; the presence of granulocytes is always an abnormal finding. A large number of granulocytes often heralds bacterial meningitis. White cells can also indicate reaction to repeated lumbar punctures, reactions to prior injections of medicines or dyes, central nervous system hemorrhage, leukemia, recent epileptic seizure, or a metastatic tumor. When peripheral blood contaminates the withdrawn CSF, a common procedural complication, white blood cells will be present along with erythrocytes, and their ratio will be the same as that in the peripheral blood.

The finding of erythrophagocytosis, where phagocytosed erythrocytes is 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.

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

• Measurement of chloride levels may aid in detecting the presence of tuberculous meningitis.
• Glucose is usually 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 in order to 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 and hypercapnia.
• 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.
• The enzyme lactate dehydrogenase can be measured to help distinguish meningitides of bacterial origin, which are often associated with high levels of the enzyme, from those of viral origin in which the enzyme is low or absent.
• 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.
• 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.
• CSF can be sent to the microbiology lab for various types of smears and cultures to diagnose infections.
• Polymerase chain reaction (PCR) has been a great advance in the diagnosis of some types of meningitis. 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, it saves cost of hospitalization.