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Observations on muscle pain in man, with particular reference to pain during needle electromyography
Abstract:
Muscle pain receptors have been studied in man. During the advance of an EMG needle pain is most regularly experienced as the muscle fascia is pierced. Further advancing the needle is usually quite painless. However, there are scantily distributed points within the muscle (`pain spots') which may give rise to pain if encountered by the advancing needle. The nature of the responsible receptors is obscure but it is likely that pain may sometimes be caused by activation of nerve fibres (presumably from these receptors) coursing through the muscle rather than by activation of the receptors themselves. Intramuscular bleeding is unlikely to contribute often to the pain of needle electromyography. Mechanically sensitive `pain spots' are more painful than other areas when stimulated electrically or injected with hypertonic (6%) saline. This suggests a common receptor. The high electrical threshold and relative invulnerability to pressure of afferent fibres from these receptors suggest that they are mainly of small diameter. These findings are discussed in relation to experimental work on pressure-pain receptors in animals.
Insights
Pain during electromyography (EMG) often stems from piercing muscle fascia or encountering specific `pain spots.
Area of Science:
- Neuroscience
- Pain Research
- Human Physiology
Background:
- Needle electromyography (EMG) involves inserting needles into muscles to assess electrical activity.
- Patient-reported pain during EMG is a common concern, with specific points within muscles identified as particularly sensitive.
- The precise nature of the receptors responsible for this pain remains unclear.
Purpose of the Study:
- To investigate the characteristics of pain experienced during needle electromyography in humans.
- To identify the potential receptors and nerve fibers involved in muscle pain during EMG procedures.
- To differentiate pain sources, such as mechanical stimulation versus intramuscular bleeding.
Main Methods:
- Investigated pain perception during needle insertion and advancement in human muscles.
- Electrically stimulated and injected hypertonic saline into identified `pain spots' within muscles.
- Compared pain thresholds and responses to mechanical pressure.
Main Results:
- Pain during EMG is primarily associated with piercing the muscle fascia or encountering localized `pain spots.'
- Mechanically sensitive `pain spots' exhibit heightened sensitivity to electrical stimulation and hypertonic saline injection, suggesting a common receptor.
- Afferent nerve fibers from these receptors appear to be of small diameter, indicated by their high electrical threshold and low pressure sensitivity.
Conclusions:
- The study suggests that specific, mechanically sensitive receptors in muscles are responsible for pain during EMG.
- Pain may arise from the activation of nerve fibers associated with these receptors rather than the receptors themselves.
- Findings support the existence of distinct pain pathways in muscles relevant to clinical procedures like EMG.