Pain Processes in Tennis Elbow Visualized with PET scanning

The physiologic mechanisms in soft tissue pain such as chronic tennis elbow can now be seen clearly using the imaging technology positron emission tomography (PET), according to Swedish radiologists.

The new study was demonstrated by researchers from Uppsala University (Sweden), and the findings were published October 2013 in the journal PLOS ONE. Chronic pain is a significant problem, with substantial socioeconomic costs and suffering of the individual. Musculoskeletal pain is the most typical type of pain and is one of the most common reasons for consultation in health care. However, pain from soft tissues (i.e., pain from muscles, tendons, and ligaments) is still lacking effective approaches for localization and diagnosis of underlying pathophysiologic processes.

This means that diagnosis still depends on clinical examination, which provides no guidance regarding what mechanisms might underlie the pain. Therefore, treatment relies solely on an empirical basis. An improved diagnostic technique that allows not only diagnosis of localization of the painful tissue processes, but also can provide guidance regarding what pathophysiologic mechanisms are involved, would therefore be very valuable.

Dr. Magnus Peterson from Uppsala University is utilizing PET imaging in combination with a specific tracer for the signal receptor NK1 to visualize such injuries. The tracer is injected into the blood where it circulates through the body and binds to available NK1 receptors. The signal from the radioactive tracer can then be captured as an image outside the body using PET.

This is the first time an up-regulation of NK1 receptors has been visualized by diagnostic imaging in painful tissue in humans. The study distinctly reveals an image of elevated levels of NK1 in the painful area compared with the healthy arm.

Following tissue injury, there is an up-regulation of the neuropeptide substance P and its receptor NK1. This happens not only in the dorsal horn of the spinal cord, but also in the peripheral painful tissue. This up-regulation process is part of an interaction between peripheral nerves, immune cells, and the tissue itself that seems to help guide the body’s own repair process. In chronic tennis elbow, this up-regulation of the substance P-NK1 system lingers on. This is what the researchers have succeeded in visualizing with the aid of PET and the marker for NK1.

The technology has potential, but the procedure is still quite expensive. PET is a complex procedure, which requires high-end equipment. “In the future, we hope to be able to develop less expensive markers that enable us to use the method in everyday clinical practice. We also aim to create markers for other physiological processes that we know are active in chronic soft tissue pain,” concluded Dr. Peterson.

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