Frank in Fort Lauderdale, Florida asks:
"I have been told that a Transdermal Electrical Nerve Stimulation Unit can help with my back pain. Could you explain how these things work?"
T J Salih, Senior Chartered Physiotherapist at the back2normal back and neck clinic, London replies:
"Transcutaneous or transdermal electrical nerve stimulation (TNS or TENS) is an electrotherapy modality used to relieve pain. Back pain is just one of the conditions that can benefit from this modality, which is used in the treatment of many chronic pain syndromes. Research has shown it to be an effective pain relief treatment in over 60% of patients.
"It is a non-invasive treatment which uses the application of a pulsed electrical current via surface electrodes applied to the skin. There are many types of TENS unit on the market. They are normally pocket sized and battery operated. Most have controls for pulse width (or duration measured in microseconds), pulse shape (usually rectangular), frequency (the rate of electrical pulse delivery, measured in Hertz) and intensity (which indicates the strength of the current, measured in milli Amps).
"To understand how TENS works, one has to have a basic understanding of pain. For pain to be perceived there is usually a stimulation of a type of sensory nerve called a 'pain receptor', by a noxious physical or chemical agent. This stimulation is passed up via nerve impulses in the spinal cord, to the brain where the pain is appreciated at the conscious level. If the pain stimulation to the brain is modulated using a TENS unit, then pain relief can be achieved.
"One method of pain relief can be achieved when TENS acts as a physiological inhibitor of impulses from the pain receptor, in a process often referred to as the 'Pain Gate Mechanism'. This occurs because, when set at a higher frequency, the TENS unit stimulates different pain receptors which override the painful stimulus. This is the electrotherapy equivalent of rubbing your knee after you've fallen on it. The counter stimulation provides pain relief.
"The other mechanism of action of TENS, when set on a lower frequency, is that the brain will produce its own natural painkillers, known as endorphins. By setting the TENS machine to alternate between higher and lower frequencies, you not only get a local 'nerve block' but also a general endorphin release which both help with pain reduction.
"Once switched on the patient experiences a gentle tingling or buzzing sensation from the electrodes. Unlike drug treatment, there are few side effects with TENS treatment and the pain relief mechanisms are completely natural. One problem may be patient allergy to the electrodes, but this is quite rare. Pain relief provided by TENS frequently outlasts the treatment period by a few hours and in some cases up to a few days. This can allow patients to complete their physiotherapy exercises and facilitate a complete recovery."
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