Pain in multiple sclerosis

Multiple Sclerosis (MS) is a chronic, progressive disease which presents as a variety of cognitive, motor and sensory deficits (Compston and Coles, 2008). Pain is one of the most common and often severe symptoms of the disease. It is associated with poorer general health, and its management is therefore an important therapeutic target. People with MS can suffer from neuropathic pain as a direct result of damage to the central nervous system, or nociceptive pain, as a result of changes to the musculoskeletal system, secondary to disease progression. This was the first epidemiological study to measure the prevalence, characteristics, and impact of MS-related pain, using validated, IMMPACT-recommended measures. Neuropathic pain, common in MS, is a challenge to manage and is shown to impact on a person health-related quality of life (HR-QOL). Subsequently, the second part of this study explored the impact of Transcutaneous Electrical Nerve Stimulation (TENS) on neuropathic pain in MS, in a randomised controlled trial. A postal survey design was used to target the MS population of the NHS Ayrshire and Arran health board area, who completed a questionnaire on their pain experience (n=302). Clinically significant pain, defined as ongoing bothersome pain, was experienced by over two-thirds (71.5%), whilst chronic pain, defined as pain present for at least six months, was experienced by over half (59.2%) of the MS population. Neuropathic pain, assessed using the PainDETECT screening tool, was experienced by almost one third (32.7%) of the sample, with a further 14.7% identified as potentially having neuropathic pain. Thus 47.4% of the sample could potentially have neuropathic pain, which is higher than previous estimates, and that experienced by the general population. Approximately half the population experienced painful tonic spasms (44.5%) and dysaesthetic pain (56.2%). Burning pain, unpleasant paraesthetic sensations (i.e. crawling, tingling), and sharp pain were commonly experienced in the population with neuropathic pain. Multiple logistic regression analysis revealed Type of MS (p=0.001) and disability level (Guys Neurological Disability Scale (GNDS) (p<0.001) as independent predictors of neuropathic pain, possibly related to the pathophysiology of the disease. Neuropathic pain was shown as statistically more severe (using the 11-point Numerical Rating Scale of pain intensity (NRS-11) (p<0.001), more emotionally unpleasant (using the SF-MPQ) (p<0.001), with greater sleep disturbance (p<0.001), than nociceptive pain. Despite over two-thirds (68.5%) of those with neuropathic pain currently using prescribed, pain-relieving medication, over half (53.7%) still experienced severe (7-10 on NRS-11) pain. The presence of neuropathic also had a significantly negative impact on HR-QOL (EQ-5D) (p<0.001). The results of the epidemiological study increase understanding of the extent and demanding nature of pain in MS. Clinically, it will also facilitate timely screening for the neuropathic pain subtype, to minimise its impact on HR-QOL. Following the epidemiological findings, a randomised, double-blind, placebo-controlled trial, explored the efficacy of Transcutaneous Electrical Nerve Stimulation (TENS) in the treatment of chronic, neuropathic pain in MS (n=46). Participants were recruited from the MS Service, NHS Ayrshire and Arran, with a diagnosis of lower limb neuropathic pain (score of ≥19 on the PainDETECT Screening tool for neuropathic pain), experienced for a minimum of six months. For the active TENS group, standard ‘Conventional’ TENS settings were applied, whilst a low frequency, low intensity, long pulse duration electrical current was used for the placebo application, which has no known analgesic effect, but still provides a sensory stimulus. Both groups used the TENS machine for a minimum of four hours/day, for a two-week period. Two long self-adhesive, hypo-allergenic electrodes were placed paravertebrally over the lumbar spine to stimulate the spinal nerve roots. The primary outcome measure was the (NRS-11), whilst secondary outcome measures included the Neuropathic Pain Scale (NPS), and the Patients Global Impression of Change (PGIC). Level of pain related interference on function was measured using the Brief Pain Inventory (BPI). Compared to the control group, the group receiving active TENS demonstrated a statistically (p<0.001) and clinically significant reduction in the intensity of neuropathic pain over the two-week intervention period. It was particularly effective for the burning, and sharp neuropathic pain qualities, that were commonly associated with neuropathic pain in the epidemiological study. TENS was also shown to reduce the emotional unpleasantness of pain (the affective component), which was high in those with neuropathic pain in the epidemiological study. This may have implications for the role of TENS in managing the psychological aspect of chronic neuropathic pain. TENS has no effect on pain–related interference on function, possibly due to the relatively short TENS intervention period. Future studies should explore longer intervention periods to explore the longer-term effects of TENS for pain in MS. The pharmacological management of neuropathic pain is not without its challenges. TENS as an inexpensive, non-invasive modality, with no side-effects, could be considered for the management of neuropathic pain, a common phenomenon in the MS population.