Disruption of thermal perception in a multiple sclerosis patient with central pain

Thermal Grill Illusion in Post-Stroke Patients: Analysis of Clinical Features and Lesion Areas

Purpose

In the thermal grill illusion, participants experience a feeling similar to burning pain. The illusion is induced by simultaneously touching warm and cool stimuli in alternating positions. In post-stroke pain, central sensitization is caused by a variety of factors, including damage to the spinothalamic tract and shoulder pain. Because the thermal grill illusion depends on central mechanisms, it has recently been suggested that it may be a useful indicator of central sensitization. Therefore, we hypothesized that post-stroke patients who are more likely to experience central sensitization may also be more likely to experience a thermal grill sensation of pain and discomfort than the likelihood among those who are less likely to experience central sensitization. However, the effects of the thermal grill illusion in post-stroke patients have not yet been reported. In this pilot study, we conducted the thermal grill illusion procedure in post-stroke patients and analyzed the relationship between clinical somatosensory functions and thermal grill sensations. We also conducted brain imaging analysis to identify brain lesion areas that were associated with thermal grill sensations.

Patients and Methods

Twenty patients (65.7 ± 11.9 years old) with post-stroke patients participated in this study. The thermal grill illusion procedure was performed as follows: patients simultaneously touched eight water-filled copper bars, with the water temperature adjusted to provide alternate warm (40°C) and cold (20°C) stimuli.

Results

Thermal grill sensation of pain and discomfort tended to be associated with the wind-up phenomenon in bedside quantitative sensory testing and thermal grill sensation of discomfort was also related to damage to the thalamic lateral nucleus.

Conclusion

These findings suggest that the thermal grill illusion might measure central sensitization, and that secondary brain hyperactivity might lead to increased thermal grill sensations.

Thermal grill illusion of pain in patients with chronic pain: a clinical marker of central sensitization?

ABSTRACT

The thermal grill illusion of pain (TGIP) is a paradoxical burning pain sensation elicited by the simultaneous application of innocuous cutaneous warm and cold stimuli with a thermode ("thermal grill") consisting of interlaced heated and cooled bars. Its neurophysiological mechanisms are unclear, but TGIP may have some mechanisms in common with pathological pain, including central sensitization in particular, through the involvement of N-methyl- d -aspartate receptors. However, few studies have investigated TGIP in patients with chronic pain and its clinical relevance is uncertain. We hypothesized that the TGIP would be increased in comparison with controls in patients with fibromyalgia or irritable bowel syndrome, which are regarded as typical "nociplastic" primary pain syndromes related to changes in central pain processing. We compared the sensations elicited by a large range of combinations of temperature differentials between the warm and cold bars of a thermal grill applied to the hand between patients with fibromyalgia (n = 30) or irritable bowel syndrome (n= 30) and controls (n = 30). The percentage of TGIP responses and the intensity and unpleasantness of TGIP were significantly greater in patients than controls. Furthermore, positive correlations were found between TGIP intensity and clinical pain intensity and between TGIP intensity and the cold pain threshold measured on the hand. These results are consistent with our working hypothesis of shared mechanisms between TGIP and clinical pain mechanisms in patients with nociplastic chronic pain syndromes and suggest that TGIP might represent a clinical marker of central sensitization in these patients.

Pain quality of thermal grill illusion is similar to that of central neuropathic pain rather than peripheral neuropathic pain

OBJECTIVES

Application of spatially interlaced innocuous warm and cool stimuli to the skin elicits illusory pain, known as the thermal grill illusion (TGI). This study aimed to discriminate the underlying mechanisms of central and peripheral neuropathic pain focusing on pain quality, which is considered to indicate the underlying mechanism(s) of pain. We compared pain qualities in central and peripheral neuropathic pain with reference to pain qualities of TGI-induced pain.

METHODS

Experiment 1:137 healthy participants placed their hand on eight custom-built copper bars for 60 s and their pain quality was assessed by the McGill Pain Questionnaire. Experiment 2: Pain quality was evaluated in patients suffering from central and peripheral neuropathic pain (42 patients with spinal cord injury, 31 patients with stroke, 83 patients with trigeminal neuralgia and 131 patients with postherpetic neuralgia).

RESULTS

Experiment 1: Two components of TGI-induced pain were found using principal component analysis: component 1 included aching, throbbing, heavy and burning pain, component 2 included itching, electrical-shock, numbness, and cold-freezing. Experiment 2: Multiple correspondence analysis (MCA) and cross tabulation analysis revealed specific pain qualities including aching, hot-burning, heavy, cold-freezing, numbness, and electrical-shock pain were associated with central neuropathic pain rather than peripheral neuropathic pain.

CONCLUSIONS

We found similar qualities between TGI-induced pain in healthy participants and central neuropathic pain rather than peripheral neuropathic pain. The mechanism of TGI is more similar to the mechanism of central neuropathic pain than that of neuropathic pain.

Neuropathic Pain in Multiple Sclerosis and Its Animal Models: Focus on Mechanisms, Knowledge Gaps and Future Directions

Multiple sclerosis (MS) is a multifaceted, complex and chronic neurological disease that leads to motor, sensory and cognitive deficits. MS symptoms are unpredictable and exceedingly variable. Pain is a frequent symptom of MS and manifests as nociceptive or neuropathic pain, even at early disease stages. Neuropathic pain is one of the most debilitating symptoms that reduces quality of life and interferes with daily activities, particularly because conventional pharmacotherapies do not adequately alleviate neuropathic pain. Despite advances, the mechanisms underlying neuropathic pain in MS remain elusive. The majority of the studies investigating the pathophysiology of MS-associated neuropathic pain have been performed in animal models that replicate some of the clinical and neuropathological features of MS. Experimental autoimmune encephalomyelitis (EAE) is one of the best-characterized and most commonly used animal models of MS. As in the case of individuals with MS, rodents affected by EAE manifest increased sensitivity to pain which can be assessed by well-established assays. Investigations on EAE provided valuable insights into the pathophysiology of neuropathic pain. Nevertheless, additional investigations are warranted to better understand the events that lead to the onset and maintenance of neuropathic pain in order to identify targets that can facilitate the development of more effective therapeutic interventions. The goal of the present review is to provide an overview of several mechanisms implicated in neuropathic pain in EAE by summarizing published reports. We discuss current knowledge gaps and future research directions, especially based on information obtained by use of other animal models of neuropathic pain such as nerve injury.

Central neuropathic pain in multiple sclerosis is associated with impaired innocuous thermal pathways and neuronal hyperexcitability

OBJECTIVE

About a third of patients with multiple sclerosis (MS) suffer from chronic and excruciating central neuropathic pain (CNP). The mechanism underlying CNP in MS is not clear, since previous studies are scarce and their results are inconsistent. Our aim was to determine whether CNP in MS is associated with impairment of the spinothalamic-thalamocortical pathways (STTCs) and/or increased excitability of the pain system.

DESIGN

Cross sectional study.

SETTING

General hospital.

SUBJECTS

47 MS patients with CNP, 42 MS patients without CNP, and 32 healthy controls.

METHODS

Sensory testing included the measurement of temperature, pain, and touch thresholds and the thermal grill illusion (TGI) for evaluating STTCs function, and hyperpathia and allodynia as indicators of hyperexcitability. CNP was characterized using interviews and questionnaires.

RESULTS

The CNP group had higher cold and warm thresholds (p < 0.01), as well as higher TGI perception thresholds (p < 0.05), especially in painful body regions compared to controls, whereas touch and pain thresholds values were normal. The CNP group also had a significantly greater prevalence of hyperpathia and allodynia. Regression analysis revealed that whereas presence of CNP was associated with a higher cold threshold, CNP intensity, and the number of painful body regions were associated with allodynia and hyperpathia, respectively.

CONCLUSIONS

CNP in MS is characterized by a specific impairment of STTC function; the innocuous thermal pathways, and by pain hyperexcitability. Whereas CNP presence is associated with STTC impairment, its severity and extent are associated with pain hyperexcitability. Interventions that reduce excitability level may therefore mitigate CNP severity.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

Organization of the Thermal Grill Illusion by Spinal Segments

Objective

A common symptom of neuropathy is the misperception of heat and pain from cold stimuli. Similar cold allodynic sensations can be experimentally induced using the thermal grill illusion (TGI) in humans. It is currently unclear whether this interaction between thermosensory and nociceptive signals depends on spinal or supraspinal integration mechanisms. To address this issue, we developed a noninvasive protocol to assess thermosensory integration across spinal segments.

Methods

We leveraged anatomical knowledge regarding dermatomes and their spinal projections to investigate potential contributions of spinal integration to the TGI. We simultaneously stimulated a pair of skin locations on the arm or lower back using 1 cold (∼20°C) and 1 warm thermode (∼40°C). The 2 thermodes were always separated by a fixed physical distance on the skin, but elicited neural activity across a varying number of spinal segments, depending on which dermatomal boundaries the 2 stimuli spanned.

Results

Participants consistently overestimated the actual cold temperature on the skin during combined cold and warm stimulation, confirming the TGI effect. The TGI was present when cold and warm stimuli were delivered within the same dermatome, or across dermatomes corresponding to adjacent spinal segments. In striking contrast, no TGI effect was found when cold and warm stimuli projected to nonadjacent spinal segments.

Interpretation

These results demonstrate that the strength of the illusion is modulated by the segmental distance between cold and warm afferents. This suggests that both temperature perception and thermal–nociceptive interactions depend upon low‐level convergence mechanisms operating within a single spinal segment and its immediate neighbors. Ann Neurol 2018;84:463–472

Mechanisms and pharmacology of neuropathic pain in multiple sclerosis

The neuropathic pain of multiple sclerosis is quite prevalent and severely impacts quality of life. A few randomized, placebo-controlled, blinded clinical trials suggest that cannabis- and anticonvulsant-based treatments provide partial pain relief, but at the expense of adverse events. An even smaller, but emerging, number of translational studies are using rodent models of experimental autoimmune encephalomyelitis (EAE), which exhibit pain-like behaviors resembling those of Multiple sclerosis (MS) patients. These studies not only support the possible effectiveness of anticonvulsants, but also compel further clinical trials with serotonin-norepinephrine reuptake inhibitors, the immunosuppressant drug rapamycin, or drugs which interfere with glutamatergic neurotransmission. Future behavioral studies in EAE models are essential toward a new pharmacotherapy of multiple sclerosis pain.

One night of total sleep deprivation promotes a state of generalized hyperalgesia: a surrogate pain model to study the relationship of insomnia and pain

Sleep disturbances are highly prevalent in chronic pain patients. Understanding their relationship has become an important research topic since poor sleep and pain are assumed to closely interact. To date, human experimental studies exploring the impact of sleep disruption/deprivation on pain perception have yielded conflicting results. This inconsistency may be due to the large heterogeneity of study populations and study protocols previously used. In addition, none of the previous studies investigated the entire spectrum of nociceptive modalities. To address these shortcomings, a standardized comprehensive quantitative sensory protocol was used in order to compare the somatosensory profile of 14 healthy subjects (6 female, 8 male, 23.5 ± 4.1 year; mean ± SD) after a night of total sleep deprivation (TSD) and a night of habitual sleep in a cross-over design. One night of TSD significantly increased the level of sleepiness (P<0.001) and resulted in higher scores of the State Anxiety Inventory (P<0.01). In addition to previously reported hyperalgesia to heat (P<0.05) and blunt pressure (P<0.05), study participants developed hyperalgesia to cold (P<0.01) and increased mechanical pain sensitivity to pinprick stimuli (P<0.05) but no changes in temporal summation. Paradoxical heat sensations or dynamic mechanical allodynia were absent. TSD selectively modulated nociception, since detection thresholds of non-nociceptive modalities remained unchanged. Our findings show that a single night of TSD is able to induce generalized hyperalgesia and to increase State Anxiety scores. In the future, TSD may serve as a translational pain model to elucidate the pathomechanisms underlying the hyperalgesic effect of sleep disturbances.

Neuropathic pain in animal models of nervous system autoimmune diseases

Neuropathic pain is a frequent chronic presentation in autoimmune diseases of the nervous system, such as multiple sclerosis (MS) and Guillain-Barre syndrome (GBS), causing significant individual disablement and suffering. Animal models of experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune neuritis (EAN) mimic many aspects of MS and GBS, respectively, and are well suited to study the pathophysiology of these autoimmune diseases. However, while much attention has been devoted to curative options, research into neuropathic pain mechanisms and relief has been somewhat lacking. Recent studies have demonstrated a variety of sensory abnormalities in different EAE and EAN models, which enable investigations of behavioural changes, underlying mechanisms, and potential pharmacotherapies for neuropathic pain associated with these diseases. This review examines the symptoms, mechanisms, and clinical therapeutic options in these conditions and highlights the value of EAE and EAN animal models for the study of neuropathic pain in MS and GBS.

Duloxetine in patients with central neuropathic pain caused by spinal cord injury or stroke: a randomized, double-blind, placebo-controlled trial

The mechanisms underlying central neuropathic pain are poorly understood. Pain inhibitory mechanisms including sertononergic and norepinephrine systems may be dysfunctional. In this randomized, double-blinded, placebo-controlled trial we evaluated the effects of duloxetine on pain relief (spontaneous pain and evoked pain), tolerability, health status, and quality of life in patients with central pain related to cerebrovascular lesions or spinal cord lesions. At baseline and eight weeks following start of treatment subjects were evaluated with standard measures of efficacy: pain intensity (primary efficacy variable), quantitative sensory testing, health status and quality of life (secondary efficacy variables). Forty-eight patients received escalating doses of either duloxetine (60 and 120mg/day) or matching placebo capsules. In both groups, patients started with 1 capsule per day. If pain relief was insufficient, patients were titrated to a higher dose. A trend towards a decrease in mean pain score after eight weeks was observed for duloxetine treatment (p=0.056). Duloxetine alleviated dynamic (p=0.035) and cold allodynia (p<0.001) significantly better than placebo. Tactile pain and pressure pain thresholds did not improve significantly. The duloxetine group showed a significant improvement for the bodily pain domain of the SF36 (p=0.035). No significant differences were observed in the other domains of the SF36, the Pain Disability Index, and the EQ-5D. While this trial showed no significant effect on pain intensity, duloxetine revealed a biologic effect. It would be worthwhile to suspend our judgement and to perform more studies to evaluate the role of duloxetine in modulation of the symptoms of central neuropathic pain.

Successful treatment of central pain in a multiple sclerosis patient with epidural stimulation of the dorsal root entry zone

OBJECTIVE

We report a case of central pain successfully treated by epidural placement of spinal cord stimulator electrodes. Neuromodulation of primary afferent fibers and the underlying dorsal root entry zone provided effective analgesia whereas traditional lead placement over the dorsal columns on a prior occasion had not been effective. The rationale for this technique based on current understanding of the mechanisms of central pain and the risk/benefit considerations are discussed.

CASE REPORT

A 52-year-old woman presented with a 2-year history of pain in the lateral hand secondary to a demyelinating episode in the C2-4 spinal cord secondary to multiple sclerosis. Medications, sympathetic blocks, and acupuncture had been ineffective. One year after an unsuccessful single-lead trial of spinal cord stimulation over the cervical dorsal columns, a dual-lead trial of spinal cord stimulation over the lateral cervical spinal cord and dorsal roots provided significant analgesia, prompting a successful permanent implant.

OUTCOME MEASURES

Responses on the Brief Pain Inventory short form and quantitative thermosensory testing data were collected at two timepoints 16 days apart under two conditions: no stimulation and single-lead stimulation of cervical primary afferents and underlying spinal cord.

RESULTS

The patient's questionnaire responses indicated significantly improved pain scores with lateral-lead neuromodulation that was associated with a reduction in her baseline heat hypoalgesia.

CONCLUSIONS

Lateral-lead spinal cord stimulation may be effective for some central pain syndromes through a partial restoration of homeostatic small-fiber signaling. Neuroanatomical and physiological data in a larger population of patients will be required to predict the best responders to this therapeutic modality.

The impact of pain and other symptoms on quality of life in women with relapsing-remitting multiple sclerosis

The purpose of this study was to assess pain, fatigue, depression, sleep disturbance, and quality of life (QOL) in women with relapsing-remitting multiple sclerosis (RRMS) compared with healthy controls. A prospective, cross-sectional, matched-control study was conducted in women with RRMS compared with healthy women. Compared with healthy women, women with RRMS had (a) greater pain presence over 7 days (67%), (b) higher pain intensity, and (c) more pain interference. Pain had a negative impact on fatigue, depression, and sleep in both groups. In all participants, fatigue, depression, and sleep disturbance contributed to decreased mental QOL (mental component summary of QOL scores). Pain has significant nursing implications for women with RRMS. Pain often occurs in association with fatigue, depression, and sleep disturbance, which can lead to a decreased mental QOL.

Pain associated with multiple sclerosis: systematic review and proposed classification

Pain is common in patients with multiple sclerosis (MS), but estimates of its prevalence have varied widely. The literature describing pain in MS patients spans four decades and has employed a range of different methodologies. We undertook a systematic review in order to summarize current understanding of the association between MS and pain and provide a basis for the design and interpretation of future studies. The point prevalence of pain in patients with MS is nearly 50%, and approximately 75% of patients report having had pain within one month of assessment. Pain adversely affects most aspects of health-related quality of life, including functional domains such as the ability to work. The presence of pain in patients with MS is associated with increased age, duration of illness, depression, degree of functional impairment, and fatigue. Several different types of pain are found in patients with MS, including extremity pain, trigeminal neuralgia, Lhermitte's sign, painful tonic spasms, back pain, and headache. Putative mechanisms of pain in patients with MS are discussed, and a classification of pain in MS is proposed. Few randomized clinical trials of treatments for MS pain have been conducted, and the limitations of current knowledge regarding approaches for treating MS pain are discussed. Suggestions for future studies that would increase understanding of the natural history, mechanisms, and treatment of pain in patients with MS are presented.

Qualitative and quantitative characterization of the thermal grill

Concurrent applications to the skin of spatially adjacent bands of innocuous warm and cool stimuli would elicit a peculiar sensation, known as the 'thermal grill illusion'. To validate the thermal grill as a research tool, this two-phase study qualitatively characterizes this peculiar sensation and further quantitatively establishes the temperature matching of the most intense/noxious thermal grill stimulations at two different time points. The temperature combinations (degrees C) tested were: 18/18, 42/42, 18/42, 20/20, 40/40, 20/40, 22/22, 38/38, 22/38, 24/24, 36/36 and 24/36. None of the subjects reported pain with single temperature combinations. However, hot associated with pain and burning sensations were reported in all mixed temperature combinations tested. The VAS scores for pain were significantly elevated for 20/40 and 18/42 in comparison to 22/38 and 24/36 (P<0.007). At the 3-second time point, the matching temperatures (+/-SD) of 20/40 and 18/42 were 45.7+/-1.8 (range 44-48) and 46.6+/-1.5 (range 44-48) degrees C, respectively, whereas the matching temperatures for the single temperature combinations were similar to the set temperatures. Importantly, at the 10-second time point, none of the combinations were significantly greater than the highest of the pair of stimuli. The time course variation in the perception of the combined stimuli suggests an adaptation occurred in central processing.

Hyperalgesia in an animal model of multiple sclerosis

Many individuals with multiple sclerosis (MS) experience clinically significant pain, yet the underlying neural mechanisms for MS pain are not understood. Experimental autoimmune encephalomyelitis (EAE) is a well-studied disease in rodents that mimics many clinical and pathological features of MS, including central nervous system inflammation and demyelination. To determine whether EAE is an appropriate model for MS-related pain, nociceptive responses in both male and female SJL mice were measured before and after immunization with myelin proteolipid protein peptide 139-151 (PLP(139-151)) in complete Freund's adjuvant to induce 'active' EAE. To determine if changes in nociception were due to direct effects of encephalitogenic T cells, nociceptive responses in female SJL mice were measured following the transfer of activated, PLP(139-151) specific T cells to induce 'passive' EAE. Both forepaw and tail withdrawal latencies to a radiant heat stimulus were measured. In both active and passive EAE, there was an initial increase in tail withdrawal latency (hypoalgesia) that peaked several days prior to the peak in motor deficits during the acute disease phase. During the chronic disease phase, tail withdrawal latencies decreased and were significantly faster than control latencies for up to 38 days post-immunization. This hyperalgesia was seen in both sexes and in both active and passive EAE models. Forepaw withdrawal latencies remained within 1-2 s of baseline latencies for the entire testing period, indicating that the hypoalgesia and hyperalgesia were most pronounced in clinically affected body regions. These results suggest that both active and passive EAE are useful models of MS-related pain.