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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.

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