A spinal tap (also known as a lumbar puncture) is a procedure whereby a sample of cerebrospinal fluid (CSF) is taken from close to the spinal cord. At the same time a blood sample is taken usually from the arm and a quantity of blood serum is isolated. Both of these samples are then processed using a technique called electrophoresis. A positive spinal tap will produce oligoclonal bands in the CSF but not in the blood serum. These bands indicate a type of immune system activity. Although uncomfortable, the spinal tap itself is often not too painful, whereas in the period following the tap, the patient may experience dizziness, nausea, vomiting and severe headaches, occasionally for as much as a week. There are a few rare but serious side-effects of spinal taps.
95% of people with a definite diagnosis of MS exhibit oligoclonal bands on a spinal tap. This may sound impressive but so do 90% of people with Sub-Acute Sclerosing Panencephalitis and 100% of people with Herpes Simplex Encephalitis among other conditions. Positive spinal taps are indicative of an immunological response but they are not diagnostic for a particular condition. That 5% of PwMS do not exhibit oligoclonal banding means that spinal taps neither rule-in nor rule-out MS.
The primary purpose of CSF analysis should be to rule out other conditions than multiple sclerosis. Although they can be highly suggestive of MS, they do not, in themselves, provide definitive disgnosis. Indeed, I myself, was given a definite diagnosis based on medical history, clinical examination, MRI and evoked potential tests - I declined to have a spinal tap.
Before MRI, electrophoresis of spinal fluid played a major role in supporting diagnoses and underpinned the Poser criteria. Now, however, these criteria have become overshadowed by MRI and, if an MRI is positive, the new diagnostic criteria (2001) allow for a definitive diagnosis without laboratory support. The old "Laboratory supported Definite MS" has been dispensed with.
However, CSF analysis technology is still advancing and researchers continue to look for definitive molecular markers of MS. Should they find such a marker, spinal taps will reassume their importance. Other researchers are looking into urine and blood for markers and we can hope that they are successful and spinal taps become completely unnecessary to the diagnosis of multiple sclerosis.