Electrical Stimulation – From Snake Oil to Mainstream Treatment Modality

Electrochemical processes in both excitable and non-excitable living cells may be affected by application of constant or time-variable external electrical fields. The most noticeable examples of application of electrical field across the cell membrane are excitations (“firings”) of neurons and contractions of muscle cells.

The use of electrical fields was limited throughout the majority of human history by absence of electrical generators and absence of means to deliver controlled electrical fields to the targeted tissues. The first documented report dating back to 46 CE refers to the use of electrogenic (Torpedo) fish for treatment of gout and headache. Galvani’s discovery of bioelectricity and development of electrostatic generators in the 18^th century paved the way to widespread applications of electrical fields in the 19^th and beginning of 20^th century. However, use of electrical fields without proper understanding of underlying mechanism of action and without appropriate controls, together with sometimes ridiculous claims of miracle treatment, resulted in unreliable clinical outcomes and discredited the entire field of electrical stimulation and neuromodulation. In the pioneering years electrical stimulation was often compared to snake oil treatment, referring to fraudulent health products and unproven medicine.

Revival and expansion of the field of neuromodulation began in the latter half of the 20^th century and developed a momentum which continues to the present day. This revival is attributed to major technological, scientific, and regulatory developments in the mid 20^th century. It is also attributed to scientific documentation of clinical benefits of electrical stimulation.

• Gait theory was introduced by Melzack and Wall (1965) to explain physiological mechanism for electroanalgesic effect, helping to revive the interest in use of neuromodulation for pain treatment.
• The invention of the transistor in 1947 by Shockley, Bardeen and Brattain paved the way to development of small size reliable stimulators, which could be wearable externally or implanted. Subsequent invention, development, and miniaturization of integrated circuits enabled building ever more sophisticated circuits for generation and delivery of stimulation modalities.
• Tighter control in the USA by Food and Drug Administration (FDA) and its worldwide counterpart regulatory agencies cleaned the field from the false claims and ensured safety and reliability of the neuromodulation devices.
• As compared to other treatment modalities, such as drugs, electrical stimulation is site specific, it can be immediately turned on and off, its intensity can be adjusted by the patient as needed in real time, and use of electrical stimulation does not cause addiction, such as in the case of opioids.

Electrical stimulation can be delivered to the targeted location using transcutaneous, percutaneous or fully implanted approaches. Each of these approaches has combination of advantages and disadvantages related to invasiveness of the procedure, repeatability and reliability of application of the stimulation, effectiveness, and to (unpleasant) sensations associated with application of electricity.

• Implantable stimulators
  • Implantable heart pacemakers and defibrillators
  • Implantable spinal cord stimulators for treatment of pain and overactive bladder (OAB)
  • Implantable peripheral nerve stimulators for treatment of peripheral pain and OAB
  • Implantable gastric stimulators
  • Implantable deep brain stimulators for treatment of Parkinson’s disease, epilepsy, muscle dystonia and depression
• Transcutaneous and percutaneous stimulators
  • Treatment of peripheral pain and OAB
  • Stimulation of muscles as part of functional electrical stimulation (FES) or for strengthening and prevention of muscle atrophy

Electrical stimulation expanded to non-excitable tissues in such fields as disruption of mitosis of cancer cells, enhancing wound healing, and bones re-growth.