Altered resting-state functional connectivity of default mode network in brachioradial pruritus.

BACKGROUND: Patients with chronic pruritus (CP) have a low quality of life, thus it is important to gain a better understanding of the underlying processes. Previous functional magnetic resonance imaging studies at rest (rsfMRI) have shown that mainly areas associated with the default mode network (DMN), sensorimotor (SMN), frontoparietal (FPN) and salience networks (SN) are involved in the processing of itch in patients with chronic pruritus (CP), as well as the cortico-striatal circuit, which is involved in the motoric preparation of scratching. rsfMRI studies on functional connectivity (FC) patterns of resting-state networks (RSNs) in patients with inflammatory atopic dermatitis (AD) or with neuropathic brachioradial pruritus (BRP) compared with healthy controls (HC) are lacking. OBJECTIVES: The main goals of this study were to investigate whether functional connectivity within networks and areas associated with itch detection and processing are altered in patients with AD and BRP compared with matched healthy controls by rsfMRI, respectively. METHODS: Patients with AD (n = 28) and with BRP (n = 28) were compared with corresponding matched healthy controls by rsfMRI. Group-specific RSNs were identified by independent component analysis (ICA) and between-group differences in the RSNs were analysed by dual regression technique. Seed-based functional connectivity was analysed in several itch-related brain regions belonging to the DMN, SN and FPN, respectively. RESULTS: ICA and seed-based analyses revealed decreased functional connectivity in BRP compared with HC specially within the DMN including the precuneus and cingulate cortex. For AD patients in comparison with HC, as well as when BRP and AD patients were compared directly, no significant FC differences at rest were seen. CONCLUSIONS: Our findings point towards decreased FC particularly in the DMN at rest in patients with BRP. These results seem to indicate that central connectivity patterns at rest differentially encode itch in BRP and AD.

[Pruritus-a long journey from neurophysiology to the clinic]. / Pruritus ­ ein weiter Weg von der Neurophysiologie zur Klinik.

BACKGROUND: The mutual exchange of results between basic sciences and clinical research as well as their translation into practice, also with regard to chronic pruritus, is currently to be seen as an ambition or hope rather than established practice. OBJECTIVE: In view of the rapid developments in the field of neurophysiological basics of pruritus, the aim is to clarify how these new concepts can be brought in line with clinical understanding. MATERIALS AND METHODS: A review is provided. RESULTS: After the peripheral and spinal processing pathways for pruritus in the mouse were characterized with molecular markers, we are currently working on the translation of this information to the only functionally defined nerve fiber classes in humans. However, it is still unclear whether these processing pathways are crucial for the explanation of chronic pruritus in patients, since inflammation or neuropathy can significantly alter nerve populations and neuronal networks. Therefore, molecular target structures, which have emerged from results of basic research, need to be verified in patients. The gold standard, however, remains the patient with clinical observation and testing. Specific stimulation methods from neurophysiology can help to test hypotheses from basic research directly on patients, while also providing impulses for further development of research concepts. CONCLUSIONS: Translation in medical research is now perceived by many researchers as a hackneyed buzzword. In the field of pruritus research, however, the exchange of results and concepts based on the mutual appreciation of expertise appears attractive, highly relevant, and promising.

[Erythromelalgia: skin redness and pain]. / Erythromelalgie: rote Haut und Schmerz.

Erythromelalgia is a rare disease that is associated with hemato-oncological diseases or after taking certain drugs and toxins, but it can also occur as an independent clinical picture, for example, due to mutations in the sodium channel NaV1.7. Clinically, there is a characteristic triad of attack-like burning pain and skin redness in the area of the distal extremities, which can be alleviated by excessive cooling. The attacks are triggered by heat, exertion, and stress. The diagnosis is primarily made clinically and can be confirmed by genetic testing if a sodium channel NaV1.7 mutation is present. Important differential diagnoses are complex regional pain syndrome, the non-freezing cold injury, and small fiber neuropathies. Therapy is multidisciplinary and has to be planned individually and include physical therapy and psychotherapy as well as drug therapy as integral components.

[New findings regarding the neurobiology of pruritus]. / Aktuelles zur Neurobiologie von Pruritus.

Chronic pruritus may arise from different conditions, including dermatological, systemic, neurologic, psychiatric, and psychosomatic diseases, leading to a substantial decrease in the quality of life of affected patients. The neurobiological mechanisms involved in chronic pruritus are not yet fully understood. However, in recent years important achievements have been made in this regard. This article aims to provide an overview of the current understanding of these mechanisms. The complex network of neurons, keratinocytes, inflammatory cells, cytokines, and neurotrophic factors which play a role in the development and maintenance of chronic pruritus are highlighted, as well as the pruritogens involved in pruritic diseases in humans. Additionally, the importance of neuropathy and scratch-induced changes for the pathophysiology of chronic pruritus are discussed. The new findings on the neurobiological mechanisms underlying chronic pruritus have already led to the development of novel therapies, e. g., monoclonal antibodies against specific interleukins, which are important for pruritus transmission. A deeper understanding of the neurobiological mechanisms is necessary in order to develop specifically targeted therapeutic options and thus provide better care for affected patients.

[Neurophysiology of atopic pruritus]. / Neurophysiologie des atopischen Pruritus.

Pruritus is one of the major symptoms of inflammatory skin diseases and strongly affects the quality of life in patients. Although the perception of pruritus and pain are closely intertwined, pruritus represents a distinct sensation, which is also significantly different to pain at a neurophysiological level. The pathophysiological basis of chronic and acute pruritus is not fully understood. Besides histamine, a plethora of different neuromediators of itch, including neurotrophins, neuropeptides and their corresponding receptors, have been identified. In atopic dermatitis the release of these mediators leads to an activation of immune cells, such as mast cells and eosinophilic granulocytes, which in turn release neuromediators and cytokines that activate peripheral neurons. This review focuses on the neurophysiological interactions which regulate pruritus and summarizes the function of neurological and inflammatory mediators in atopic pruritus.

The Quest for more Research on Painful Diabetic Neuropathy.

A 62-year-old diabetologist diagnosed himself to have diabetes type-2, with an HbA1c of 9.5. Five months after lifestyle intervention and a multi-drug approach, HbA1c was 6.3, systolic blood pressure was below 135mmHg and BMI reduced to 27. But he suffered from severe painful diabetic neuropathy. Therefore he decided to visit his friend, a famous neuroscientist at an even more famous university. He asked him several plain questions: 1. What is the natural course of painful diabetic neuropathy? 2. Why do I have, despite almost normalizing HbA1c, more problems than before? 3. Are you sure my problems are due to diabetes or should we do a nerve biopsy? 4. Are there imaging techniques helpful for the diagnosis of this diabetic complication, starting in the distal nerve endings of the foot and slowly moving ahead? 5. Can you suggest any drug, specific and effective, for relieving painful diabetic neuropathy? This review will use the experts' answers to the questions of the diabetologist, not only to give a summary of the current knowledge, but even more to highlight areas of research needed for improving the fate of patients with painful diabetic neuropathy. Based on the unknowns, which exceed the knowns in diabetic neuropathy, a quest for more public support of research is made.

Pain thresholds, supra-threshold pain and lidocaine sensitivity in patients with erythromelalgia, including the I848Tmutation in NaV 1.7.

OBJECTIVES: Nociceptive thresholds and supra-threshold pain ratings as well as their reduction upon local injection with lidocaine were compared between healthy subjects and patients with erythromelalgia (EM). METHODS: Lidocaine (0.25, 0.50, 1.0 or 10 mg/mL) or placebo (saline) was injected intradermally in non-painful areas of the lower arm, in a randomized, double-blind manner, to test the effect on dynamic and static mechanical sensitivity, mechanical pain sensitivity, thermal thresholds and supra-threshold heat pain sensitivity. RESULTS: Heat pain thresholds and pain ratings to supra-threshold heat stimulation did not differ between EM-patients (n = 27) and controls (n = 25), neither did the dose-response curves for lidocaine. Only the subgroup of EM-patients with mutations in sodium channel subunits NaV 1.7, 1.8 or 1.9 (n = 8) had increased lidocaine sensitivity for supra-threshold heat stimuli, contrasting lower sensitivity to strong mechanical stimuli. This pattern was particularly clear in the two patients carrying the NaV 1.7 I848T mutations in whom lidocaine's hyperalgesic effect on mechanical pain sensitivity contrasted more effective heat analgesia. CONCLUSION: Heat pain thresholds are not sensitized in EM patients, even in those with gain-of-function mutations in NaV 1.7. Differential lidocaine sensitivity was overt only for noxious stimuli in the supra-threshold range suggesting that sensitized supra-threshold encoding is important for the clinical pain phenotype in EM in addition to lower activation threshold. Intracutaneous lidocaine dose-dependently blocked nociceptive sensations, but we did not identify EM patients with particular high lidocaine sensitivity that could have provided valuable therapeutic guidance. SIGNIFICANCE: Acute pain thresholds and supra-threshold heat pain in controls and patients with erythromelalgia do not differ and have the same lidocaine sensitivity. Acute heat pain thresholds even in EM patients with the NaV 1.7 I848T mutation are normal and only nociceptor sensitivity to intradermal lidocaine is changed. Only in EM patients with mutations in NaV 1.7, 1.8 or 1.9 supra-threshold heat and mechanical pain shows differential lidocaine sensitivity as compared to controls.

[Update on the cutaneous neurobiology of pruritus]. / Aktuelles zur kutanen Neurobiologie von Pruritus.

The pathogenesis of chronic and acute pruritus is not yet completely understood. Interactions of neurons with resident and nonresident skin cells seem to play an important role in the regulation of pruritus. Neuronal cells which express specific receptors and are capable of releasing neuromediators play an active role in this interaction. Furthermore, released neuromediators can activate immune cells including mast cells and eosinophils, which are increased in the inflammatory infiltrate of many pruritic skin diseases. Mast cells and eosinophils express receptors for neuromediators themselves. In addition, they can release neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and cytokines including interleukin (IL)-31 which correlate with disease activity in patients with inflammatory skin diseases including atopic dermatitis and induce neuronal outgrowth. In part, a correlation of these mediators has also been described with pruritus. Although the interplay between transient and resident cells in the skin with peripheral nerves, mast cells, and eosinophils plays an important role in the mutual activation, the neurobiological mechanisms that lead to pruritus are not completely clear yet.

Short lasting transient effects of a capsaicin 8% patch on nociceptor activation in humans.

BACKGROUND: At high concentration, the TRPV-1 agonist capsaicin de-sensitizes nociceptors and reduces the intra-epidermal nerve density. METHODS: We investigated the effects of a 5 × 10 cm capsaicin 8% patch on C- and A-delta-nociceptor activation in ten healthy subjects before and at days 1-3-7-21 after patch application. Thermal thresholds, infrared thulium-YAG laser-evoked potentials (LEP) and heat pain (numeric rating scale, NRS, 0-10), electrically induced pain (10 pulses, 1.5-fold pain threshold intensity, five randomized series of 5-10-20-50-100 Hz), and axon-reflex flare (laser Doppler imaging) were recorded. RESULTS: Thermal hypoesthesia developed upon capsaicin 8% treatment. Warmth detection thresholds increased at day 1-3, heat pain thresholds were increased by about 2.6 °C after day 3, and laser-evoked heat pain remained significantly reduced for 7 days. Axon-reflex flare responses (days 1-3), but not supra-threshold electrically induced pain were significantly reduced by the capsaicin patch. CONCLUSIONS: Axonal nociceptor function assessed by electrical excitability tests supplements threshold tests of nociceptive endings. The differential analgesic effects of 8% capsaicin patches may be attributed to the kinetics of capsaicin and the different depth of nociceptive nerve fibres, yet, the time course does not match the long-lasting analgesia observed in neuropathic pain patients treated with the same patch. WHAT DOES THIS STUDY ADD?: Axonal nociceptor function assessed by supra-threshold electrical excitability tests did not coincide with capsaicin-induced transduction changes supplementing threshold measures of terminal nociceptor endings. Threshold measurements do not reflect the sustained effect of pain relief seen in neuropathic pain patients. Capsaicin-sensitive nociceptors responsible for spontaneous pain are either not specifically tested with currently available sensory stimulation protocols or have higher capsaicin sensitivity or slower recovery under neuropathic conditions.

Laser-evoked potentials mediated by mechano-insensitive nociceptors in human skin.

OBJECTIVES: Laser-evoked potentials (LEP) were assessed after peripheral nerve block of the lateral femoral cutaneous nerve (LFCN) in healthy volunteers from partially anesthetized skin areas to differentially stimulate mechano-insensitive nociceptors. METHODS: An ultrasound-guided nerve block of the LFCN was performed in 12 healthy male subjects with Ropivacain 1%. After 30 min, the nerve block induced significantly larger anesthetic areas to mechanical stimuli than to electrical stimuli revealing an area of differential sensitivity. LEPs, reaction times and pain ratings were recorded in response to the laser stimuli of (1) completely anesthetic skin, (2) mechano-insensitive, but electrically excitable skin ('differential sensitivity'), (3) normal skin. RESULTS: LEP latencies in the area of differential sensitivity were increased compared to unaffected skin (228 ± 8.5 ms, vs. 181 ± 3.6 ms, p < 0.01) and LEP amplitudes were reduced (14.8 ± 1.2 µV vs. 24.6 ± 1.7 µV, p < 0.01). Correspondingly, psychophysically assessed response latencies in the differentially anesthetic skin were increased (649 ms vs. 427 ms, p < 0.01) and pain ratings reduced (1.5/10 vs. 5/10 NRS, p < 0.01). CONCLUSION: The increase in LEP latency suggests that mechano-insensitive heat-sensitive Aδ nociceptors (MIA, type II) have a slower conduction velocity or higher utilization time than mechano-sensitive type II Aδ nociceptors. Moreover, widely branched, slowly conducting and mechano-insensitive branches of Aδ nociceptors can explain our finding. LEPs in the differentially anesthetized skin provide specific information about a mechanically insensitive but heat-sensitive subpopulation of Aδ nociceptors. These findings support the concept that A-fibre nociceptors exhibit a similar degree of modality specificity as C-fibre nociceptors.

Mechano-sensitive nociceptors are required to detect heat pain thresholds and cowhage itch in human skin.

BACKGROUND: Mechano-sensitive and mechano-insensitive C-nociceptors in human skin differ in receptive field sizes and electrical excitation thresholds, but their distinct functional roles are yet unclear. METHODS: After blocking the lateral femoral cutaneous nerve (NCFL) in eight healthy male subjects (3-mL Naropin(®) 1%), we mapped the skin innervation territory being anaesthetic to mechanical pin prick but sensitive to painful transcutaneous electrical stimuli. Such 'differentially anaesthetic zones' indicated that the functional innervation with mechano-sensitive nociceptors was absent but the innervation with mechano-insensitive nociceptors remained intact. In these areas, we explored heat pain thresholds, low pH-induced pain, cowhage- and histamine-induced itch, and axon reflex flare. RESULTS: In differentially anaesthetic skin, heat pain thresholds were above the cut-off of 50°C (non-anaesthetized skin 47 ± 0.4°C). Pain ratings to 30 µL pH 4 injections were reduced compared to non-anaesthetized skin (48 ± 9 vs. 79 ± 6 VAS; p < 0.01). The axon reflex flare area did not differ between these zones (7.8 ± 1.4 cm(2) vs. 8.3 ± 0.5 cm(2) ). Histamine iontophoresis still caused pruritus in differentially anaesthetized skin in five of eight subjects (VAS 26 ± 14), whereas itch upon cowhage spicules was absent (VAS 0 vs. 29 ± 11 in non-anaesthetized skin). CONCLUSIONS: We conclude that activation of mechano-insensitive nociceptors is sufficient to provoke itch by histamine- and acid-induced pain. The mechano-sensitive nociceptors are crucial for cowhage-induced itch and for the assessment of heat pain thresholds.

A three-axis SQUID-based absolute vector magnetometer.

We report on the development of a three-axis absolute vector magnetometer suited for mobile operation in the Earth's magnetic field. It is based on low critical temperature dc superconducting quantum interference devices (LTS dc SQUIDs) with sub-micrometer sized cross-type Josephson junctions and exhibits a white noise level of about 10 fT/Hz(1/2). The width of superconducting strip lines is restricted to less than 6 µm in order to avoid flux trapping during cool-down in magnetically unshielded environment. The long-term stability of the flux-to-voltage transfer coefficients of the SQUID electronics is investigated in detail and a method is presented to significantly increase their reproducibility. We further demonstrate the long-term operation of the setup in a magnetic field varying by about 200 µT amplitude without the need for recalibration.

Differential sensitization of silent nociceptors to low pH stimulation by prostaglandin E2 in human volunteers.

BACKGROUND: Inflammatory mediators activate and sensitize nociceptors. Tissue acidosis with low pH of 5.5 often accompanies inflammation and could enhance inflammatory pain and sensitization. METHODS: Action potentials from single mechano-responsive (CM) and mechano-insensitive (CMi) C-nociceptors of cutaneous fascicles of the peroneal nerve in healthy volunteers were recorded by microneurography. Low pH solutions with and without prostaglandin E2 (PGE2) were injected twice (with an interval of approximately 5 min) into two spots of the receptive fields of C-fibres. Heat thresholds of the C-fibres were obtained before and after each injection. RESULTS: Injections of the low pH solutions immediately induced phasic responses in CM nociceptors, whereas CMi fibres responded after a delay of several seconds with a sustained response. More CMi fibres than CM fibres showed ongoing discharge after low pH injection, but the duration and intensity of the responses to the first low pH injection did not differ between them. Upon repetition, duration and intensity of the pH responses increased more than twofold in CMi fibres only. Furthermore, combined application of pH and PGE2 sensitized the response in CMi fibres only. In contrast, heat activation thresholds were sensitized by the combination of low pH and PGE2 in both fibre classes. CONCLUSIONS: Our results confirm nociceptor class independent heat sensitization by PGE2 which is probably mediated by transient receptor potential vanilloid 1 phosphorylation. However, prolonged and increased pain responses in humans upon low pH/PGE2 stimulation appear to be primarily dependent on CMi fibres, whereas CM nociceptors appear crucial for phasic responses.

Differential time course of NGF-induced hyperalgesia to heat versus mechanical and electrical stimulation in human skin.

BACKGROUND: Nerve growth factor (NGF) causes early heat and delayed mechanical hyperalgesia. Axonal transport might contribute to lasting responses. Temporal hyperalgesia development was investigated by administering NGF in paraspinal skin. Transient receptor potential ankyrin 1 (TRPA1) is up-regulated by NGF and chemical responsiveness to cinnamon aldehyde (TRPA1 agonist) was quantified. METHODS: Eight healthy volunteers received 1 µg human recombinant NGF (i.d. 50 µL) to L4/L5 processi spinosi skin. Mechanical, thermal and electrical sensitization was assessed at 3-6 h and at days 1, 2, 3, 5, 7, 10, 14 and 21, and pain upon cinnamon aldehyde (20%, 60 µL) recorded at days 3 and 21. RESULTS: Heat hyperalgesia developed with an initial maximum at 3 h [heat pain threshold -3.9°; peak pain ratings +22 visual analogue scale (VAS)] that decreased by day 1, subsequently increased to a maximum around day 5 (-5 ± 0.2 °C, +41 ± 4 VAS), and thereafter declined to ∼20% at day 21. Mechanical and electrical hyperexcitability developed within 3 days and gradually increased to peak between days 14 and 21. Pain intensity upon cinnamon aldehyde stimulation was doubled at the NGF site at day 3 and was still increased by about 50% at day 21. CONCLUSIONS: NGF causes immediate heat hyperalgesia probably linked to an up-regulation and sensitization of transient receptor potential vanilloid 1 and possibly other proteins involved in heat transduction. The delayed mechanical hyperalgesia is apparently independent of the time required for axonal transport of NGF receptor complexes. Local mRNA translation at axonal terminals and protein accumulation is hypothesized being involved in sustained NGF-evoked hyperalgesia.

Axonal hyperexcitability after combined NGF sensitization and UV-B inflammation in humans.

BACKGROUND: Both nerve growth factor (NGF) and ultraviolet-B (UV-B) irradiation sensitize nociceptive nerve endings and increase axonal excitability of nociceptors. Combining NGF and UV-B treatment is supra-additive for sensory sensitization and even caused spontaneous pain in about 70% of the subjects. METHODS: UV-B irradiation was performed at day 21 after intradermal NGF injection in 13 volunteers. Pain thresholds, electrically induced axon reflex erythema and pain (1.5-fold pain threshold, 5-100 Hz) was analysed at days 22, 24, 28, 35, 49 and 70 and correlated to hyperalgesia and spontaneous pain. RESULTS: Electrical pain threshold after combined NGF/UVB was reduced below single treatment at 24 h but not at 72 h post-UV-B irradiation. At the NGF/UV-B site, electrical pain was enhanced at all frequencies compared with single NGF and UV-B sites at 24 and 72 h with pain ratings exceeding control values about twofold to threefold [65 ± 7 vs. 25 ± 8 visual analogue scale (VAS) (24 h) and 55 ± 9 vs. 22 ± 5 VAS (72 h)]. Hyperalgesia to electrical stimulation correlated with hyperalgesia to pinprick (Spearman r = 0.44; p < 0.001, Bonferroni corr.) and supra-threshold heat (Spearman r = 0.55; p < 0.001) stimulation at 24 h only. Electrical pain thresholds at the NGF/UV-B site weakly correlated to spontaneous pain levels (Spearman r = 0.3; p = 0.025, without Bonferroni correction). In contrast, electrically induced pain or axon reflex erythema did not correlate to spontaneous pain levels. CONCLUSIONS: The combination of NGF and UV-B increases axonal excitability that contributes to hyperalgesia and might also facilitate ongoing spontaneous pain.

[Cross-sectional field 14 pain medicine. Implementation of the German Pain Society (DGSS) core curriculum in the model study course MaReCuM]. / Querschnittsbereich 14 Schmerzmedizin. Umsetzung des Kerncurriculums der Deutschen Schmerzgesellschaft im Modellstudiengang MaReCuM.

BACKGROUND: The recent introduction of amendments to the medical licensure laws led to the introduction of the field of pain medicine into the study program "Human Medicine". The implementation has to be completed by all medical faculties before 2016. MATERIAL AND METHODS: Pain medicine was implemented into the model study course"MaReCuM" at the medical faculty in Manheim as a compulsory subject in the year 2010. It is structured into five sections in a longitudinal manner. The core section is the "pain awareness week" in the fifth academic year of the medical studies. The content and structure is based on the German Pain Society (DGSS) curriculum. For the purpose of this study the examination results and the student evaluation forms from the academic years 2010/2011 and 2011/2012 were analyzed. RESULTS: The students regarded pain medicine as being highly relevant concerning its impact on the professional activities. The competence to develop a specific and individual therapy was of special interest. A good coordination of the contents of teaching between preclinical and clinical teaching was considered to be of major importance. CONCLUSIONS: The DGSS curriculum is a useful tool for the implementation of pain medicine in a study program. In order to improve access to basic pain medicine in general, a combined teaching program consisting of pain medicine and general medicine could be helpful. Pain medicine could be used as a guide for teaching contents of outpatient medicine.