From the Guidelines
The correct answer is "Reducing input from the periphery may also reduce activity of hyperexcitable neurons in the spinal cord." When diagnostic nerve blocks are used to determine peripheral pain locations, a key problem is that they don't just block peripheral nerve transmission but can also affect central pain processing.
- This central effect can make it difficult to determine if pain relief resulted from blocking the specific peripheral nerve that was causing the pain or from dampening central sensitization processes.
- The use of neurolytic agents on peripheral nerves can lead to neuritis, resulting in symptoms more difficult to control than the original pain, as noted in studies such as 1.
- Understanding this limitation is crucial when interpreting diagnostic nerve block results in clinical practice, especially considering that peripheral nerve blocks are rarely used as the principal pain treatment and are always used together with systemic combined analgesia, as stated in 1 and 1.
- The potential for nerve damage and increased peripheral nerve firing, as well as the inability to effectively block activity in multiple branches of a nerve, are also considerations, but the primary issue in interpreting diagnostic nerve block results is the effect on central pain processing.
- This phenomenon can lead to false positive results where patients experience pain relief even when the blocked nerve isn't the primary source of their pain, highlighting the need for careful interpretation of diagnostic nerve block outcomes, as informed by the most recent guidelines such as those found in 1.
From the Research
Potential Problems with Diagnostic Nerve Blocks
- Nerve block injections can cause nerve damage and result in increased peripheral nerve firing, which may mask the cause of the original pain.
- Reducing input from the periphery may also reduce activity of hyperexcitable neurons in the spinal cord, potentially affecting the interpretation of results.
- Activity in multiple branches of a nerve cannot be blocked effectively, making it challenging to localize pain accurately. All of the above options are potential problems when interpreting the results of a diagnostic nerve block, as they can influence the outcome and make it difficult to determine the peripheral location of pain 2, 3, 4, 5, 6.
Limitations of Diagnostic Nerve Blocks
- The use of diagnostic nerve blocks lacks thorough documentation of clinical usefulness, and their validity is incompletely proved 2.
- There is a risk of false-positive responses, and controls are necessary to exclude these responses 5.
- The procedures can be influenced by placebo and nocebo effects, which should be considered when interpreting the results 3.
Importance of Proper Technique and Interpretation
- Experienced clinicians have found that diagnostic nerve blocks can provide helpful information for guiding subsequent therapy, but caution is necessary when interpreting the results 2.
- A critical evaluation of the results is necessary, taking into account the potential problems and limitations of diagnostic nerve blocks 2, 3, 4, 5, 6.