Periradicular therapy, PRT for short, is a targeted injection at a single nerve root. Under image guidance a thin needle is advanced to the point where the root exits, and a local anaesthetic is injected there, usually together with an anti-inflammatory corticosteroid preparation. The aim is to dampen the pain that comes from an irritated root — in a herniated disc, a narrowing of the nerve exit opening or a sciatica that will not settle. We provide this treatment at our practice, in a dedicated room, without a hospital stay.
A PRT can dampen the pain of an irritated nerve root for a few weeks. It does not replace treatment but buys it time — and it is not an operation.
Who is PRT suitable for?
PRT is intended for pain that follows a nerve root: from the buttock into the leg, from the neck into the arm, along a particular strip, often with tingling or numbness. The precondition is that examination and imaging fit together — that the root under pressure on the MRI is the same one that explains your symptoms. The terms in your report are explained on the page on the MRI report.
- Herniated disc of the lumbar spine — the most common occasion. The guideline recommends that PRT be offered for root pain caused by a lumbar herniation if the symptoms do not settle on their own.
- Herniated disc of the cervical spine — here PRT can be considered; the evidence is thinner, and the injection demands particular care because the spinal cord and the carotid artery lie close by.
- Narrowing of the nerve exit opening — in a spinal stenosis that pinches a single root, PRT can relieve the pain; it does not change the narrowing itself.
- Unclear assignment — if the MRI shows several possible causes, a PRT with a very small amount of anaesthetic alone can clarify which root is producing the pain (diagnostic injection).
PRT is not suitable for back pain without root involvement — that is, for pain that stays in the lower back and does not run into the leg. There is no evidence for that, and the guideline advises against it. As to timing there is no fixed rule: the injection can make sense in acute symptoms, in symptoms present for weeks, or in chronic ones. For pain lasting more than twelve weeks, medication and physiotherapy should have been tried first, and the injection then belongs within an overall concept.
What happens exactly?
The treatment takes only a short time, but it calls for preparation and care at every step.
- PreparationWe examine you and look at your MRI scans — not only the report but the images, because the guideline requires anatomical particularities such as the course of the blood vessels to be checked before every injection. You bring your list of medication. Do not stop blood thinners on your own initiative; whether and how they are paused is something we decide together with you and your GP.
- Positioning and image guidanceAt the lumbar spine you lie on your front, at the cervical spine on your back or on your side. The needle is guided under image control — X-ray fluoroscopy is the standard, and computed tomography is also possible. A small amount of contrast medium shows how the drug will spread before it is injected.
- The injectionThe skin is anaesthetised locally, then the thin needle is advanced to the root. You feel pressure, sometimes briefly the familiar pain in the leg or arm — that shows the needle is in the right place. Then the anaesthetic and the corticosteroid are injected. At the cervical spine only a non-particulate corticosteroid such as dexamethasone is used; at the lumbar spine it is the first choice.
- AfterwardsYou stay with us for a while. We check strength and sensation and monitor your circulation in order to detect early complications. Within the first two weeks we would like to hear from you how you are — in person, by telephone or in writing.
One point belongs to the explanation of the treatment: as the guideline notes, no corticosteroid preparation is currently licensed for use in the spinal canal — and therefore for PRT; it describes the licensing situation in Germany as confusing. The use counts as so-called off-label use, which is recommended in guidelines and has been customary for decades, but about which we inform you expressly.
What PRT can achieve — and what it cannot
The effect is established but limited. A Cochrane analysis of 25 studies with 2,470 participants compared corticosteroid injections into the spinal canal with sham injections in sciatic pain: in the short term, that is after two weeks to three months, leg pain was on average just under 5 points lower on a scale of 0 to 100 and the limitation in everyday life a good 4 points lower — a small difference that not everyone experiences as meaningful. Put another way, as IQWiG puts it: with a sham injection the pain improved for a few weeks in 51 out of 100 people, with a corticosteroid injection in 60 out of 100.
For the targeted injection at the root under fluoroscopy in a lumbar herniated disc, the guideline sees high-quality evidence of better results than without injection. At the cervical spine there are no randomised trials; review articles report around 50 out of 100 treated people in whom the injection was rated a success — at low-quality evidence. In spinal stenosis, IQWiG considers it unclear whether injections near the spine help.
What PRT cannot do: it does not remove the herniation and does not make a canal wider. A lasting benefit is not established, and whether an injection avoids an operation cannot be predicted in the individual case. Its real value lies in bridging a phase of severe pain during which a herniation recedes on its own — and in enabling you to stay in movement and to continue physiotherapy.
Risks and side effects
Most side effects are harmless and temporary. In fewer than 5 out of 100 treated people, circulatory reactions, temporarily stronger pain or reactions to the corticosteroid occur during or shortly after the injection — hot flushes, tingling or itching, nausea, dizziness, occasionally fever. The anaesthetic can leave the leg or the arm weak or numb for a few hours; for that reason you should not drive yourself on that day and should be careful when standing up. In diabetes, blood sugar can rise temporarily; tell us if this applies to you.
Rarer are an injury to the dura with leakage of cerebrospinal fluid and headache, an infection or an allergic reaction. Very rare but serious is a haematoma in the spinal canal that presses on nerves — IQWiG puts this at about one case in 100,000 injections. Serious complications such as damage to the spinal cord or a stroke have been described in isolated cases, overwhelmingly at the cervical spine and in connection with particulate corticosteroid preparations; the guideline puts their frequency at below one hundred-thousandth. The American medicines agency FDA therefore had a warning included in the product information in 2014. The technique recommended today — image guidance, contrast medium, non-particulate corticosteroid at the cervical spine — is the answer to those cases.
Get in touch immediately if after the injection the pain increases instead of decreasing, if new weakness or numbness appears, if you develop a fever, or if bladder and bowel no longer work as usual. What else counts as a warning sign is on the page warning signs.
Before and after
Before the appointment: bring the MRI scans on CD or another storage medium, together with your list of medication. Take your medicines as usual, including blood thinners, unless we have agreed otherwise with you. If you have a fever or an acute infection, the injection is postponed. Arrange to be collected after the treatment, or to travel by public transport.
After the injection: stay quiet on the same day, move normally from the next day on. The anaesthetic works immediately and wears off after hours; the corticosteroid needs a few days. The effect can be judged at around the fourth day. Continue with physiotherapy and your own exercises — the injection is meant to make that possible, not to replace it.
- Repetition — only if the first injection worked, but not sufficiently or not for long enough. The interval is at least one to three weeks. If the first injection achieved nothing, the same injection will achieve nothing the second time either.
- No series — fixed series of three or five without assessment in between are not sensible and are expressly not recommended by the guideline.
- Amount of corticosteroid — the total dose over a year is limited; the guideline names 200 mg methylprednisolone equivalent as the upper limit. According to indications reported by IQWiG, repeated doses of corticosteroid can weaken the bones.
Alternatives
The most important alternative is supported waiting with painkillers, movement and physiotherapy — with a herniated disc, most symptoms improve on their own within weeks. Other routes of access for an injection into the spinal canal, from behind between the vertebral arches or via the sacrum, can come into consideration; at the lumbar spine the targeted injection at the root is preferred. For pain lasting months, a multimodal pain treatment can come into consideration. If root pain persists despite everything, or if paralysis occurs, microsurgical decompression of the nerve root is the next step.
Frequently asked questions
Does the injection hurt?
The skin is anaesthetised. As the needle is advanced you feel pressure, sometimes briefly the familiar radiating pain — a sign that the right root has been reached. Most people find the treatment unpleasant but quite bearable.
How quickly does PRT work and how long does the effect last?
The anaesthetic works immediately and for hours, the corticosteroid over days. The effect can be judged at around the fourth day. In the studies the relief lasted a few weeks on average; how long it will last for you cannot be said in advance.
How often may PRT be repeated?
Only where there was a recognisable but insufficient effect, and with an interval of at least one to three weeks. The number is limited by the amount of corticosteroid per year. An injection that has not worked is not repeated.
Do I have to stop blood thinners?
Not on your own. Whether a medicine is paused depends on why you take it and which one it is. The guideline requires an individual weighing-up for every patient between the risk of bleeding and the risk of a thrombosis or a stroke on stopping. We discuss that before the appointment.
Can PRT replace an operation?
Sometimes it bridges the time until the herniation has receded, and the operation is no longer needed. That cannot be predicted. Where there is a significant paralysis or where there are warning signs, PRT is not the right route — then it is a matter for surgery.
Does PRT also help with pure back pain?
No. It acts at the nerve root and therefore on the radiating pain. For low back pain without root involvement there is no evidence, and the guideline advises against it.
Do I need a referral?
No. It is useful because it brings us your history. Bring any existing images with you; everything else is on the page Your first appointment.
If you have been advised elsewhere to have a series of injections or an operation and you are unsure, you can obtain a second opinion from us. We look at your images, examine you and tell you frankly what we consider sensible.