A lumbar puncture (LP), or spinal tap, is a common diagnostic procedure where a small amount of cerebrospinal fluid (CSF)<\/a> is removed from the spinal canal.\u00a0 In neurology, this procedure is commonly used to establish a diagnosis when meningitis is suspected.\u00a0 In the context of normal pressure hydrocephalus (NPH)<\/a>, a larger amount of fluid is drained in combination with tests of gait.\u00a0 This is often referred to as a \u201ctap test\u201d.\u00a0 In this setting, the LP is performed both to confirm a diagnosis of NPH and to predict if symptomatic relief will be achieved with ventricular shunt surgery.<\/p>\n The \u201ctap test\u201d is an outpatient procedure that is typically performed in the office of a neurologist or neurosurgeon.\u00a0\u00a0 Sometimes, however, it is performed by a radiologist using fluoroscopy or CT guidance. After numbing the lower spine with lidocaine, a needle is inserted into the sac within the spinal canal that contains CSF.\u00a0 The fluid is then allowed to drain by gravity into a collection container.\u00a0 Usually, between 1 and 2 fluid ounces of fluid is obtained. The needle is then withdrawn.\u00a0 Prior to the procedure, the patient\u2019s gait is quantitatively assessed.\u00a0 This may involve a video recording of the patient walking a defined distance with measurements of speed and step length, but in some situations, more elaborate testing using computerized techniques are employed.\u00a0 These gait tests are then repeated, generally within 1 hour after draining CSF.\u00a0 If there is a clear improvement in gait following the tap, a shunt operation may be recommended.<\/p>\n CSF obtained during the tap test is usually sent to a laboratory to look for abnormalities that may point to a co-morbid or alternative neurologic disease.\u00a0 For example, tests are now available to assess for Alzheimer\u2019s disease and other forms of neuropathology.<\/p>\n It is important to recognize that gait improvement following a tap test is short-lived.\u00a0 Typically, the benefit lasts for only a few hours.\u00a0 Sometimes the effect will last into the following day, but it is rare for it to last longer than that.\u00a0 The procedure is performed to estimate whether long-term benefit will be achieved with ventricular shunt surgery.\u00a0 It is not used as a replacement for shunt surgery.<\/p>\n It is also important to appreciate that while clear gait improvement following a tap test may confidently predict a favorable response to shunt surgery, many patients with NPH who do not improve with a lumbar puncture may still benefit from a shunt.\u00a0 In medical parlance, the tap test is considered to be of high specificity but relatively low sensitivity.<\/p>\n In some cases, continuous lumbar CSF drainage<\/a> is recommended as an alternative to the tap test or when no improvement is observed after a tap test.<\/p>\n Pros of Tap Test:<\/strong><\/p>\n Cons of Tap Test:<\/strong><\/p>\n Pros of CLD:<\/strong><\/p>\n Cons of CLD:<\/strong><\/p>\n The most common adverse effect of a lumbar puncture is a headache<\/a>, and sometimes nausea.\u00a0 This is because the procedure is performed to lower pressure within the head, which can impart a stretch on membranes within the cranium that contain pain fibers.\u00a0 The headache is experienced when a patient is seated or standing, and is relieved when a patient lies flat in bed.\u00a0 Usually, the headache resolves within a few hours and is treated with only Tylenol and hydration.\u00a0 Very rarely, it can persist for several days and require an additional corrective procedure.\u00a0 Other risks, including infection, bleeding, or nerve injury, are exceedingly uncommon.<\/p>\n Sometimes the diagnosis of NPH is clearly evident after reviewing MRI or CT results, neurologic examination, neuropsychologic testing, and consideration of the patient\u2019s history.\u00a0 A tap test is often recommended when the diagnosis is not certain or if a patient (or patient\u2019s family) requires a very high degree of confidence that shunt surgery<\/a> will be helpful before consenting to neurosurgical intervention.<\/p>\n For patients diagnosed with NPH, the long-term outlook can vary.\u00a0 Intervention with treatments like ventriculoperitoneal (VP) shunting<\/a>, or sometimes endoscopic third ventriculostomy (ETV)<\/a>, can lead to significant improvements in symptoms, particularly in gait and bladder control. Cognitive benefits can also sometimes be evident.\u00a0 Many patients experience substantial relief, allowing them to maintain a more independent lifestyle.<\/p>\n The effectiveness of treatment can depend on the timing of diagnosis.\u00a0 Current evidence suggests that early detection and intervention may improve prognosis.\u00a0 While ventricular shunt surgery can be highly effective, some patients may still experience ongoing challenges, particularly with cognitive function, even after shunting.\u00a0 This may reflect the presence of a co-morbid neurologic process such as stroke, microvascular disease, Alzheimer\u2019s disease, or other neurodegenerative pathologies.\u00a0 In addition, shunts<\/a> may fail over time, requiring revision surgery and other forms of adjustment.\u00a0 It is also not uncommon for patients who exhibit pronounced initial benefit from shunt surgery to deteriorate over subsequent years, even when their shunts are functioning optimally.\u00a0 The explanation for this phenomenon is sometimes not clear.<\/p>\n In conclusion, lumbar puncture remains an important diagnostic and treatment-planning tool for NPH. It helps identify patients who may benefit from surgical interventions, providing valuable insights for guiding optimal care.<\/p>\n Information you can trust! This article was produced by the Hydrocephalus Association, copyright 2024. We would like to thank James Golomb, MD<\/a>, for his valuable contribution and expert input.<\/i>
\nThe Tap Test and Its Significance:<\/h2>\n
\nTap test vs. Continuous Lumber CSF Drainage (CLD):<\/h2>\n
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\nRisks and Considerations of Lumbar Puncture<\/h2>\n
\nDiagnosis Beyond the Tap Test<\/h2>\n
\nLong-Term Outlook for NPH Patients<\/h2>\n
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\nThis article is designed to provide helpful information on the subjects discussed. It is not intended as a substitute for treatment advice from a medical professional. For diagnosis or treatment of any medical condition, consult your doctor.<\/i><\/em><\/p>\n\r\n Was this resource helpful?<\/h3>\r\n <\/div>\r\n