Many people with chronic muscle pain have a condition called myofascial pain syndrome (MPS). Pain over a large area with muscle tenderness is common. Trigger points (TrPs) are the main finding with this condition. TrPs are hypersensitive nodules that can be felt in a muscle. TrPs can be active or latent. Active means they cause a painful pattern when the muscle is at rest. Latent means the TrP must be palpated (rubbed or pressed) to cause symptoms.
In a previous study, these same authors found out that chemicals released during inflammation are present around the active TrPs. And they discovered that the chemical mix around latent TrPs also changes over time.
In this study, muscle tissue was compared for active TrPs, latent TrPs, and normal tissue. A very thin needle was inserted into the muscle. Tiny amounts of tissue were removed and analyzed. Two muscles were tested: the upper trapezius (in the neck and upper shoulder) and the gastrocnemius (calf). The gastrocnemius was an uninvolved muscle far away from the influence of the upper trapezius.
Various measures tested and compared included pH (measure of acidity); substance P (present with painful conditions); and levels of immune cells linked with inflammation. Immune-based inflammatory cells included bradykinin, tumor necrosis factor (TNF), and interleukins. Concentrations of other biochemicals, peptides, and hormones were also tested.
The authors described in detail the equipment and method used to collect the tissue samples.The specific tests used to analyze the samples were also discussed. These included capillary electrophoresis, electrochromatography, and nine other analyses used for each specific chemical being studied.
Results showed lower pH for the active TrP muscles. There were also higher levels of all substances tested in the active TrP muscles. Results for the muscle tissue with latent TrPs were similar to normal muscle tissue. This study confirms the fact that biochemicals known to be present with pain and inflammation are elevated around TrPs.
The fact that these substances were present (but not as much) in normal tissue was important. The authors suggest this may mean that substances normally associated with pain and fatigue can be present in areas of muscle other than around TrPs.
Muscle activity requiring oxygen delivery, muscle contraction, and relaxation may generate these chemicals. When they reach an elevated level, then tenderness and referred pain from TrPs may occur. It’s also possible that the increased levels of biochemicals signal pain receptors. Then pain receptors send pain messages through the spinal cord to the brain.
This way of studying TrPs does not harm the muscle or cause further pain and TrPs. The researchers will continue to study muscle pain related to TrPs in an effort to find more effective ways to treat and prevent them from developing.