Introduction
Injections are commonly used by pain specialists, both to help diagnose the painful condition and to help treat the painful condition.
This guide will help you understand
- the difference between diagnostic and therapeutic injections
- what the common medications injected are intended to do
- the risks and benefits of injections for pain
Rationale
What is the difference between diagnostic and therapeutic injections?
Injections used for pain management can be divided into two categories: diagnostic injections and therapeutic injections.
Diagnostic injections are intended to help your doctor determine what part of the body is causing the pain you are experiencing. The part that is causing the pain is sometimes referred to as the pain generator. Diagnostic injections are used by your doctor to determine the pain generator by a process of elimination. You should also understand that there may be more than one part that is painful. There may be several pain generators.
The process of finding the pain generator begins with a careful history and physical examination. This may lead to a differential diagnosis. The differential diagnosis is a list of all the possibilities that the physician can think of that best fit with the findings from the initial history and physical examination. Once the differential diagnosis list has been determined, the goal is to figure out which item on the list is actually causing your symptoms.
The next step may be to obtain x-rays, MRI scan, or CT scans. Each of these radiological tests gives your doctor information about the structure of your spine, bones and joints. These images may show abnormalities that may account for your pain. For example, a spine x-ray may show Arthritis of the joints of the spine that could be causing the pain that you are experiencing. But, simply because the structural abnormality could be causing your pain does not mean that it is. Structural abnormalities are commonly seen on radiological tests. Many of these abnormalities are not necessarily causing pain.
The rationale behind diagnostic injections is simple: If a structural abnormality identified on the radiological tests is causing your pain, and if your doctor can inject that structure to temporarily numb that and only that specific structure and the pain stops temporarily, then it makes sense that this is what is actually causing your pain.
It is also likely that you may have several abnormalities visible on the radiological tests. It may be unclear which abnormality is the cause of your symptoms. For example, you may have several intervertebral discs that appear worn out on the MRI scan of your lumbar spine. It could be that all of the discs are causing your pain - or it could be that there is only one disc causing your pain. If you are considering surgery, you would want to be sure which disc is causing the pain so that you did not undergo any additional, unnecessary surgery.
Finally, your pain may actually be coming from somewhere else in your body altogether. For example, it is not uncommon for a patient to have a worn out hip joint and a worn out lower back. When a patient with this combination of problems has hip and thigh pain, it is not always obvious whether the pain is coming from the hip joint or being referred from the lower spine - or both.
By injecting the hip joint with medication to temporarily numb the hip joint and eliminate the pain that is coming only from the hip, the physician can determine what portion of the pain is coming from the hip joint - if any - and what pain is originating from the spine. This helps diagnose the problem accurately and prevent any unnecessary procedures.
Almost all diagnostic injections follow a similar strategy. First, determine what could be causing the pain. Next, inject the structure that is most likely the cause of the pain with a medication that should reduce or eliminate the pain temporarily. If the pain is eliminated, then the structure injected is almost surely the cause of the pain. It is the pain generator.
Unlike diagnostic injections, therapeutic injections are intended to treat your problem. Therapeutic injections are used when your doctor already has a very good idea what structure is the pain generator. This means that therapeutic injections should be expected to reduce, or eliminate, your symptoms for some period of time. Injections rarely eliminate pain permanently. But, some injections may last weeks to months.
Preparations
How do I prepare for this procedure?
To prepare for the procedure your doctor may tell you to remain "NPO" for a certain amount of time before the procedure. This means that you should not eat or drink anything for the specified amount of time before your procedure. This means no water, no coffee, no tea - not anything. You may receive special instructions to take your usual medications with a small amount of water. Check with your doctor if you are unsure what to do.
You may be instructed to discontinue certain medications that affect the clotting of your blood several days before the injection. This reduces the risk of excessive bleeding during and after the injection. These medications may include the common Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) such as aspirin, ibuprofen, naproxen and many other medications that are commonly used to treat arthritis. If you are taking any type of blood thinning medication you should let your doctor know. You will most likely need to have this medication regulated or temporarily discontinued prior to the injection. Your doctor will need to determine if it is safe to discontinue these medications in order to have the injection.
You may need to arrange to have transportation both to and from the location where you will undergo the injection. Wear loose fitting clothing that is easy to take off and put on. You may wish to take a shower the morning of the procedure, using a bactericidal soap to reduce chances of infection. Do not wear jewelry or any type of scented oils or lotions.
Procedure
What happens during the procedure?
Injections are commonly performed in several different settings. Some simple injections may be done in the office. Other injections that require special equipment may be done in the operating room, the radiology department or a surgery center.
Many injections are done with the help of fluoroscopic guidance. The fluoroscope is an x-ray machine that allows the doctor to actually see an x-ray image while doing the procedure. This allows the doctor to watch where the needle goes as it is inserted. This makes the injection much safer and much more accurate. Once the needle is in the right location, a small amount of radiographic dye is injected. This liquid dye shows up on the x-ray image, and the doctor can watch where it goes. The medication used for the injection will go in the same place. The doctor wants to make sure the injection will put the medication where it can do the most good. Once the correct position is confirmed, the medication is injected, and the needle is removed.
The medications that are normally injected during a therapeutic pain injection include a local anesthetic and some type of cortisone, or steroid, medication. A local anesthetic medication, such as lidocaine or bupivicaine, is the same medication that is used numb the area when you are having dental work or having minor surgery, such as a laceration sutured. The medication causes temporary numbness lasting one hour to six hours, depending on which type of anesthetic is used.
Cortisone is an extremely powerful anti-inflammatory medication. When this medication is injected around inflamed, swollen nerves and connective tissues, it can reduce the inflammation and swelling. Decreasing inflammation reduces pain in joints. Reduced swelling can allow the nerves to function better, reducing numbness and weakness.
After Care
What happens after the procedure?
If everything goes as planned, you will be able to go home soon after the injection, probably within one hour. After most types of pain injections, you will probably not have any restrictions on activity or diet following the procedure.
When the pain injection is a diagnostic injection, your doctor will be interested in how much the pain is reduced while the anesthetic, or the numbing medication, is working. You may be given a pain diary to record what you feel for the next several hours. This is important for making decisions, so keep track of your pain.
You will be expected to cease all physical activity for 48 hours following your injection, so if you are participating in physical therapy or other therapeutic activity, be sure to let your therapist know you'll have to reschedule any appointments.
Most doctors will arrange a follow-up appointment, or phone consult, within one or two weeks after the procedure to see how you are doing and what effect the procedure had on your symptoms.
And remember, injections are not usually a cure for your pain; they are only a part of your overall pain management plan. You will still need to continue working with the other recommendations from your pain management team.