Local effects

Inserting a needle through the skin will cause firing of small-diameter fibres A-δ, C-fibres and group II/III fibres. Firing of these nerve endings will contribute to the sensation of Deqi often described by the patient as aching, fullness or warmth. Needling will cause local effects of increased blood flow in the skin and the muscle due to release of neuropeptides.

Segmental effects

Impulses from nerve fibres stimulated in the skin and muscle are transmitted into the dorsal horn of the spinal cord tissues via somatic nerves. The spinal cord receives converging information from the periphery, including skin, muscles, joints, bones and at some levels viscera. The spinal cord is also influenced by descending impulses from the brainstem and higher centres. Therapeutic effects from acupuncture may be gained by considering the segmental nerve supply of the target tissue, e.g. a painful ankle or an overactive bladder (OAB). Needling according to the segmental nerve supply provides the potential to modulate activity in the spinal cord, for example causing inhibition of the transmission of nociceptive information through the dorsal horn.

Extrasegmental and central regulatory effects

Inserting an acupuncture needle into the body will influence structures in the brainstem such as the periaqueductal grey area, as well as higher centres such as structures of the limbic, endocrine and autonomic systems. These may provide more global effects on the body such as generalized pain relief, improvement of sleep quality or mood. It is difficult to predict exactly which points will elicit these effects but major points such as LI4, LR 3, SP6 and ST36 are likely to support these responses in many patients.

Effects relating to myofascial trigger points

Needling myofascial trigger points has the potential to reduce pain and contribute to improved muscle function.

Absent or impaired sensation

Damage to sensory pathways within the nervous system may lead to impairments in sensation. The degree of impairment will depend on the site and extent of the lesion. Sensation and proprioceptive deficits may lead to considerable difficulties with balance and mobility as well as functioning of the upper limbs [2]. The loss of sensory information due to lesions within the pathways has a substantial effect on cortical responsiveness and topographical organization of the primary sensory cortex [3].

Prevalence of impaired sensation in neurological conditions

Sensory deficits are common in neurological conditions, with an estimated prevalence of up to 65% in stroke [4], 80–90% of those with multiple sclerosis [5] and most individuals with spinal cord injury. Sensory features are also prominent in peripheral neuropathies involving the sensory nerves, such as alcoholic peripheral neuropathy and the acute motor and sensory axonal neuropathy subtype of Guillain–Barré syndrome [6, 7].

Acupuncture for impaired sensation

We are unaware of any studies specifically using acupuncture to improve sensation, although studies by Napadow et al. [8] indicate that modifications of the primary sensory cortex may be induced by acupuncture. Many studies in neurorehabilitation have used various types of sensory stimulation, but these usually measure the outcome in terms of improved motor function rather than commenting on sensory function [9]. Perhaps this is an area that merits further exploration.

Abnormal sensations, including paraesthesia and pain

Pain is common and problematic in neurological conditions (Table 4.1). Effective management is needed and acupuncture may be of value in this situation. It is important to understand the nature of the pain presentation to guide acupuncture intervention and expected outcomes.

Table 4.1 Prevalence of pain in common neurological conditions

Peripheral neuropathy

Peripheral focal or generalized neuropathies involve loss of myelin and/or axonal damage of peripheral nerves. Neuropathic pain may arise from molecular changes in the area of injured or degenerating axons [12]. Hypersensitivity in the peripheral nervous system will then drive the development of hypersensitivity in the spinal cord and central pain transmission pathways.

Stroke, traumatic brain injury, spinal cord injury, multiple sclerosis

In stroke, traumatic brain injury, spinal cord injury and multiple sclerosis functional impairment of the spinothalamocortical tract conveying pain and temperature sensation from the periphery to the cortex seems crucially important in the development of neuropathic pain [5, 13–15]. In spinal cord injury evidence suggests that those individuals with more extensive reorganization of the primary somatosensory cortex experience more severe ongoing pain [16].

Parkinson’s disease

The disturbance of central processing of nociceptive information by the basal ganglia is likely to have a role in the development of central neuropathic pain in Parkinson’s disease [17, 18]. In addition dysfunction of nociceptive processing at spinal cord level is also involved [19].

Peripheral neuropathy

Studies have evaluated the use of acupuncture for peripheral neuropathy of various aetiologies (Table 4.4). These reveal some positive results, particularly the finding that acupuncture improved nerve conduction in tibial and sural nerves [20]. Further prospective research is needed.

Spinal cord injury

Studies in spinal cord injury are small. They provide hints that acupuncture may be useful for nociceptive and neuropathic pain (Table 4.5).

Multiple sclerosis

No large-scale trials have been conducted. Descriptive case reports suggest benefit from electroacupuncture at 50 Hz for painful trigeminal neuralgia [21], as well as body and ear acupuncture for leg pain and dysaesthesia affecting the hands [22, 23].

Stroke, traumatic brain injury, Parkinson’s disease and adult cerebral palsy

Descriptive case reports indicate benefits from acupuncture for central neuropathic pain in stroke [24], for nociceptive shoulder pain in stroke [25] and for central neuropathic pain in traumatic brain injury [26]. Implanted percutaneous electrical nerve stimulation (PENS) reduced chronic hemiplegic shoulder pain [27]. No large-scale studies have been conducted.

Paraesthesia and dysaesthesia

At this point it is worth mentioning abnormal sensations which are commonly reported in neurological conditions. ‘Paraesthesia’ refers to abnormal sensations which are not described as unpleasant [28]. This may include sensations such as tingling, prickling, pins and needles, burning, aching and tightness. ‘Dysaesthesia’ is defined as an unpleasant abnormal sensation and includes the more specific categories of allodynia and hyperalgesia. It is therefore included in the category of neuropathic pain [28]. Paraesthesia and dysaesthesia may represent a pure sensory phenomenon such as in cortical strokes affecting the postcentral gyrus, or may be accompanied by motor signs such as tonic spasms in multiple sclerosis [29, 30]. Paraesthesia and dysaesthesia may be spontaneous or evoked. They arise from abnormal activity in the nervous system such as ectopic impulse activity in the central or peripheral nerves, or ephaptic transmission between physically adjacent neurones in areas of demyelination [31]. These sensations cause substantial distress to some individuals. Management of these sensations follows the recommendations for neuropathic pain.

Motor dysfunction

Motor symptoms are extremely common in neurological conditions. These range from complete paralysis through to excessive muscle activity such as spasticity will be considered.

Weakness and paralysis

Damage within central or peripheral pathways controlling movement may cause weakness or complete paralysis. Weakness is very common in stroke, traumatic brain injury, multiple sclerosis and peripheral neuropathies.

Spasticity

Spasticity is a movement disorder observed in individuals with lesions of the upper motor neurone pathways, for example, in stroke, multiple sclerosis or spinal cord injury. Spasticity is classically defined as a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes [36]. It is accompanied by a range of other features such as weakness and loss of dexterity [37]. The neurophysiology of spasticity is complex but involves abnormalities in proprioceptive, cutaneous and nociceptive reflexes. Persistent spasticity may lead to adaptive changes such as soft-tissue contracture. The impact of spasticity on functional ability is unclear but for many individuals spasticity is problematic [38].