Why does a herniated disc cause leg or arm pain?

A herniated disc does two things to the nerve beside it. It presses on it, which the MRI shows. And it leaks nucleus material onto it, which the MRI cannot show. That material has been sealed away from your immune system your whole life. When it reaches the root, the body treats it as foreign. Cytokines (immune alarm signals) pour in, and the root swells. Its thread-like blood supply gets squeezed. A nerve built to carry feeling starts firing on its own. The pain down your leg or arm is mostly that chemical fire. That is why plenty of people carry a large herniation on a scan and feel nothing. Steroid at the root addresses the fire, not the fragment. That narrow aim is why it works so well in the right patient and so poorly in the wrong one.

Do epidural steroid injections work?

Left alone, herniated disc material tends to shrink. A 2015 systematic review of imaging follow-up studies found that the larger and more pushed-out the fragment, the more likely it was to shrink back. The most extruded types went away in the great majority of cases. Small bulges did so in a minority.

A few months is an easy phrase from a chair. It is a different phrase on a pick line at the Edwardsville and Pontoon Beach warehouses. Or on a rotating turn at the Granite City steel works, or a refinery shift in Wood River. There, twelve weeks of not lifting is twelve weeks of not being paid. The epidural exists for that gap.

Read the trials with that in mind. A 2012 meta-analysis in Annals of Internal Medicine and the 2020 Cochrane review both found a small short-term drop in leg pain and disability against placebo. They found no reliable long-term difference. Both pooled mixed groups at fixed time points, and many of those people were going to recover anyway. Neither measured what matters to a shift worker: back at work in week three or week twelve. The practice position: it is a bridge. It is for a patient whose radicular pain (pain running down a nerve) is severe, whose exam and imaging agree, and whose life cannot wait out the natural course. It is not a routine for everyone with a positive scan.

Which route, and why it is not interchangeable

Does an epidural steroid injection raise blood sugar?

For years I told patients with borderline A1C numbers that they were not too bad. I was wrong, and this procedure is one of the places the error shows up on a glucose meter. Corticosteroid placed at a nerve root does not stay there. A 2012 study in Spine followed diabetic patients after epidural injection. Their blood glucose climbed and took days to return to baseline. In an insulin-resistant body the rise is steeper and longer, because the liver is already ignoring the signal to stop releasing sugar and the muscle is refusing to take it up.

That body is the typical body here. On the tighter cardiometabolic criteria applied to NHANES after 2021, under 7% of US adults qualify as metabolically healthy. The older NHANES 2009–2016 figure was already under 12.2%. In this practice the share is under 3% overall, and under 1% among chronic pain patients. Metabolic inflammation raises the baseline the root starts from. It narrows the tiny blood vessels the root depends on. And it slows the resorption the injection is buying time for, which is the fragment shrinking. The third driver is not biology. It is a twelve-hour rotating shift that wrecks sleep and hands you vending-machine carbohydrate at 3 a.m. If you are diabetic, tell us before the day and expect the bloodwork conversation to be part of the visit.

How many epidural steroid injections can you have?

One injection, then an honest look at what it did. Most of the relief: the next may never be needed. Some: a repeat a few weeks later can be reasonable. None: a second identical injection is a poor bet. The question becomes whether the root was ever the source. Steroid adds up over time and costs bone, the adrenal axis and glucose. So the number of injections is a medical decision made each time against the last result, never a course booked in advance.

Planning it from the Illinois side of the river

Nothing is injected at the first visit. That appointment is the exam, the imaging review, the bloodwork order and the decision. For a patient driving from Belleville or Alton, it sets up the rest so the crossings are counted. The injection is its own appointment. The two-week check can be by phone or video where it makes medical sense, so the second bridge crossing is a decision, not a habit. With the roads clear and no traffic figured in, Edwardsville is about 40 minutes from the office, Granite City about 25, Alton about 30. There is no sedation: you are awake, the skin is numbed, and most patients drive themselves home. The exception is a limb that comes out temporarily heavy or numb, which passes within hours; if that happens, someone else drives until it wears off.

What happens during an epidural steroid injection?

Frequently asked questions

How soon will I know whether it worked?

The numbing medicine confirms within the hour that the drug reached the right root, then wears off. The steroid builds over two to seven days and is judged at two weeks. That check is described on our what to expect page.

Can I drive myself back to Illinois afterward?

Most patients do, because no sedation is used; the one reason to bring someone is a leg that comes out temporarily numb, covered in driving home after a spine injection.

I am diabetic. Is the steroid a problem for me?

Expect your glucose to run higher for several days, and check it more often. We adjust dose and plan when we know in advance. That is one reason this clinic looks at your numbers at all, as explained in why a pain clinic checks your blood sugar.

Will the injection keep me out of surgery?

For radicular pain from a herniation, it often carries a patient through the time it takes the fragment to shrink, and the operation never becomes needed. For a root that is losing strength, it does not replace a surgeon’s opinion, as the herniated disc page explains.

How painful is an epidural steroid injection?

There is no sedation, so you are awake. The skin over the target is cleaned and numbed first, and that sting is usually the worst part. As the needle nears the root you may feel a brief flash of your usual leg pain. It is uncomfortable, and it is useful, because it tells us the needle is at the right root.

How long should you rest after an epidural steroid injection?

Not long. After a short observation period you go home, and normal activity, including work, is back within two to four hours unless the limb comes out temporarily heavy or numb, which passes within hours. Keep a two-week log. Early relief is the numbing medicine; relief that builds over the following days is the steroid, and that is what we judge at two weeks.

What are the side effects of an epidural steroid injection?

The steroid does not stay at the nerve root. Blood sugar climbs and can take days to come back down, more steeply in an insulin-resistant body. So diabetic patients should check more often and tell us beforehand. A leg or arm can feel heavy or numb for a few hours. Repeated steroid adds up against bone, the adrenal system and glucose, which is why each injection is decided against the last result.

Related reading

• Sciatica
• Herniated disc
• Cervical radiculopathy
• Spinal stenosis
• When injections stop working