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Diagnostic blocks explained

One of the things that we do at Resolve Pain is to try and help make a diagnosis of what may be causing or contributing to your pain. We do this with a process called diagnostic blocks. A diagnostic block is exactly what it sounds like – we try to select an area or nerve which we think may be contributing to your pain and try to block the pain from that area to help make a diagnosis.

In a diagnostic block, a small needle is placed through the tissue with anatomical landmark guidance (finding bony or soft points in your anatomy) or ultrasound to find the right spot. We then inject a local anaesthetic into this area which will numb or ‘turn off’ that nerve for a period – usually only 4-6 hours.

The idea is that if we block one nerve or area from giving a pain signal, does that take away the pain bothering you? If it does, then we know we are in the right spot. If it does, but not entirely, such as it takes away pain in one area but not another, we will often try and block another location at the same time to see if we can settle other aspects of your pain. Or finally, if the block does not work, this outcome can also be helpful because we can rule out that possible cause and look at alternative causes and treatment options.

Remember – a diagnostic block aims to help make a diagnosis – this is the main aim of the procedure.

Nerve block under ultrasound

Are there risks with a diagnostic block? Diagnostic blocks are usually simple procedures performed in our rooms or the hospital procedural room. Depending on the injection site makes a difference to the small risks, so your doctor can explain specific risks for your condition. The most common risks are a slight flare of pain after the procedure (we are putting a needle in a sore area, and the anaesthetic will wear off) or local bruising.

Rare but possible risks include allergic reactions to the medication or damage to the nerves we inject beside. Exceedingly rare but theoretically possible risks include cardiac arrhythmias, seizures and death.

Do you inject into the nerve? No. We inject NEXT to the nerves. Can I get any weakness from the procedure? Yes – temporarily. The local anaesthetic we use can cause muscles notto get their nerve signals and therefore be weak for the duration of the drug (usually 4-6 hours). The risk of slight temporary weakness is why we ask you to have a driver with you when we are blocking areas that can affect driving muscles, such as your legs, back and neck.

Am I expected to get any long-term benefit from this procedure? No – that is not the aim of a diagnostic block. Some people get more extended benefit from the injection than the usual four to six hours. There are several possible reasons for this, but it is uncommon – so take it as a bonus if it happens. At times we will also discuss adding another therapy with the diagnostic block, such as prolotherapy, steroid or PRP. These are specific therapies that your doctor will discuss with you at the procedure, and each has different expected outcomes and may extend the length of benefit. However, any prolonged benefit is a bonus – the main aim of a diagnostic block is to make the diagnosis.

If you have pain relief>50% for two to six hrs after the procedure, then we are generally in the right spot. However, we may sometimes perform a diagnostic block and add other therapies, such as prolotherapy or PRP. The addition of other treatments is only suitable in specific situations.

These are other agents that your doctor may talk to you about at the time to try and extend the benefit that you get from the diagnostic block. In some circumstances, these can also help reduce your pain long term. But as the main reason for this procedure is a diagnostic block, any ongoing benefit is a bonus but not the main aim.

If a diagnostic block is ‘positive’ – meaning that it reduced your pain significantly, then your pain team can talk to you about longer-lasting options such as radiofrequency ablation or neurostimulation. Sometimes, having a positive block and a more precise diagnosis can lead to more focused rehabilitation and physiotherapy, which may help you to cure the problem yourself with the assistance of your care team.

A flow chart of decisions for your diagnostic block is below. The chart is just a guide; with your pain team, we may adjust these details, but this gives a framework for us to build upon.

Web MD - Nerve blocks

Medical News Today - Nerve blocks and how they work

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