Intramuscular Stimulation (IMS)

When a patient is referred for "dry needling," the term sounds simple — a needle, a muscle, a treatment. But behind that single needle lies a fundamental disagreement about what causes chronic myofascial pain, and that disagreement has significant consequences for what gets needled, how deep, and why. The split traces to two lineages that developed largely independently: Chan Gunn's work in Vancouver through the 1970s and 1980s, which drew on Melzack's gate control theory and Cannon's supersensitivity to develop the neuropathic model of MPS; and Janet Travell and David Simons' decades-long compilation of the trigger point atlas, which built the peripheral myofascial model that underpins Dry Needling worldwide.

Gunn's neuropathic model proposes that all chronic myofascial pain syndrome has its origin in "spondylogenic" neuropathy — subtle dysfunction at the spinal nerve root level arising from degenerative changes in the spine that do not produce the classic symptoms of frank radiculopathy. Gunn argued that even mild, subclinical nerve root compromise causes supersensitivity in all structures supplied by that root: skin, connective tissue, and especially muscle motor end plates. This supersensitivity — which follows Cannon's Law of Denervation — causes the affected muscles to become shortened, overreactive, and painful. Crucially, this is distinct from standard radiculopathy: there is no dermatomal numbness, no reflex change, no positive straight leg raise. Instead, there are subtle signs: skin that dermagraphs more easily, muscles that are diffusely shortened in a segmental pattern, and paraspinal tenderness at the relevant level.

The trigger point model, as codified by Travell and Simons and subsequently refined by researchers including David Simons, Robert Gerwin, and Jay Shah, proposes that myofascial pain arises from local contracture knots in muscle — palpable taut bands containing a central trigger point at the endplate zone. The Integrated Hypothesis (Simons, 2004) describes an energy crisis at the motor end plate: excessive acetylcholine release causes sustained sarcomere contraction that compresses local capillaries, creating local ischemia, acidosis, and the release of sensitizing substances (bradykinin, substance P, CGRP) that activate and sensitize nociceptors. Surface and intramuscular EMG studies have confirmed the presence of spontaneous electrical activity (SEA) in active trigger points — evidence of abnormal endplate activity that is the electrophysiological signature of the contracture knot.

Where the two models converge is in the reality of complex, chronic MPS that most specialist clinicians encounter daily. A patient with ten years of neck and shoulder pain, multi-segment degenerative cervical changes on MRI, diffuse scalene and upper trapezius trigger points, and subtle Gunn radiculopathic signs in C5-6 distribution cannot be cleanly assigned to either model exclusively. Most experienced needling practitioners have recognized this and work pragmatically: paraspinal IMS-style treatment to address the segmental neuropathic component, followed by peripheral trigger point Dry Needling to deactivate the peripheral contracture knots. The two techniques are not rivals but tools that address different levels of the same chronic pain system.

RCT evidence comparing IMS and Dry Needling directly is limited, partly because the techniques are operationally similar enough that blinding is challenging and partly because the conditions they target — chronic MPS — are notoriously heterogeneous. Systematic reviews and meta-analyses of Dry Needling for myofascial pain generally find moderate evidence for short-term pain reduction and improved pressure pain threshold compared to sham needling or no treatment, with less certainty about long-term durability. The evidence base for IMS is smaller in terms of RCTs but is supported by a substantial case series literature and the mechanistic plausibility of Gunn's model.

Head-to-head comparison studies are rare, and where they exist (e.g., cervicogenic headache, chronic low back pain), results tend to show equivalent short-term outcomes between the approaches. This is not surprising if both techniques ultimately work through shared mechanisms: mechanical disruption of contracture knots, local tissue microtrauma triggering repair processes, and modulation of peripheral and central sensitization via needle-induced afferent input. The clinical implication is that for straightforward, acute-onset MPS without radiculopathic signs, either technique is likely to be effective. The distinction in outcomes is most apparent in chronic, treatment-resistant presentations where the presence or absence of a segmental neuropathic component determines whether peripheral needling alone will produce durable relief.