Caroline Dietrich

Sensory feedback prosthesis reduces phantom limb pain: Proof of a principle

BACKGROUND Constrained functionality and phantom limb pain (PLP) are major concerns for forearm amputees. Neuroscientific investigations of PLP suggest that behaviorally relevant stimulation of the stump can decrease PLP. Furthermore the prosthesis user could use feedback information of the prosthesis hand for optimizing prosthesis motor control when handling soft and fragile objects. Somatosensory feedback information from a prosthetic hand may therefore help to improve prosthesis functionality and reduce phantom limb pain. OBJECTIVES We wanted to find out whether a two weeks training on a hand prosthesis that provides somatosensory feedback may help to improve prosthesis functionality and reduce phantom limb pain. METHODS Eight forearm amputees with phantom limb pain were trained for two weeks to use a hand prosthesis with somatosensory feedback on grip strength. RESULTS The current study demonstrates a significant increase of functionality of the prosthesis in everyday tasks. Furthermore, the study shows that usage of a prosthesis that provides somatosensory feedback on the grip strength is effective to reduce phantom limb pain. CONCLUSIONS A prosthesis with a feedback function appears to be a promising therapeutic tool to reduce phantom limb pain and to increase functionality in everyday tasks. Future studies should further investigate the scope of application of that principle.

Gray Matter Changes Following Limb Amputation with High and Low Intensities of Phantom Limb Pain

Limb amputation and chronic phantom limb pain (PLP) are both associated with neural alterations at all levels of the neuraxis. We investigated gray matter volume of 21 upper limb amputees and 14 healthy control subjects. Results demonstrate that amputation is associated with reduced gray matter in areas in the motor cortex representing the amputated limb. Additionally, patients show an increase in gray matter in brain regions that belong to the dorsal and ventral visual stream. We subdivided the patient group into patients with medium to high PLP (HPLP; N = 11) and those with slight PLP (SPLP; N = 10). HPLP patients showed reduced gray matter in brain areas involved in pain processing. SPLP patients showed a significant gray matter increase in regions of the visual stream. Results indicate that all patients may have an enhanced need for visual control to compensate the lack of sensory feedback of the missing limb. As we found these alterations primarily in the SPLP patient group, successful compensation may have an impact on PLP development. Therefore, we hypothesize that visual adaptation mechanisms may compensate for the lack of sensorimotor feedback and may therefore function as a protection mechanism against high PLP development.

The volatility of the amygdala response to masked fearful eyes.

Recently, it has been suggested that backwardly masked, and thus subliminally presented, fearful eyes are processed by the amygdala. Here, we investigated in four functional magnetic resonance imaging experiments whether the amygdala responds to subliminally presented fearful eyes per se or whether an interaction of masked eyes with the masks or with parts of the masks used for backward masking might be responsible for the amygdala activation. In these experiments, we varied the mask as well as the position of the target eyes. The results show that the amygdala does not respond to masked fearful eyes per se but to an interaction between masked fearful eyes and the eyes of neutral faces used for masking. This finding questions the hypothesis that the amygdala processes context‐free parts of the human face without awareness. Hum Brain Mapp, 2010.

Plasticity in the Visual System is Associated with Prosthesis Use in Phantom Limb Pain

The experience of strong phantom limb pain (PLP) in arm amputees was previously shown to be associated with structural neural plasticity in parts of the cortex that belong to dorsal and ventral visual streams. It has been speculated that this plasticity results from the extensive use of a functional prosthesis which is associated with increased visual feedback to control the artificial hand. To test this hypothesis, we reanalyzed data of cortical volumes of 21 upper limb amputees and tested the association between the amount of use of the hand prosthesis and cortical volume plasticity. On the behavioral level, we found no relation between PLP and the amount of prosthesis use for the whole patient group. However, by subdividing the patient group into patients with strong PLP and those with low to medium PLP, stronger pain was significantly associated with less prosthesis use whereas the group with low PLP did not show such an association. Most plasticity of cortical volume was identified within the dorsal stream. The more the patients that suffered from strong PLP used their prosthesis, the smaller was the volume of their posterior parietal cortex. Our data indicate a relationship between prosthesis use and cortical plasticity of the visual stream. This plasticity might present a brain adaptation process to new movement and coordination patterns needed to guide an artificial hand.

Brachial Plexus Block in Phantom Limb Pain: A Case Report

OBJECTIVE The purpose of this case report is twofold: first, to present evidence of long-lasting relief in a patient suffering from phantom limb pain after pharmacologically blocking his plexus brachialis and, second, to replicate results from a previous study focusing on cortical reorganization and phantom limb pain. SUBJECT Before regional anesthesia, the patient suffered from a phantom hand that cramped and was immovable. SETTING We performed a diagnostic axillary blockade of the brachial plexus to differentiate peripheral from more central contributions to phantom limb pain. RESULTS During blockade of the brachial plexus, the patient reported a reduction of phantom limb pain for the first time following years of suffering and a complete loss of cramping together with muscle relaxation of the phantom hand. Additionally, we found cortical reorganization in the primary somatosensory cortex (re-reorganization). Strikingly, the relaxed phantom limb together with the reduction of phantom limb pain remained preserved even 6 months after blockade of the brachial plexus. CONCLUSIONS A single temporary blockade of the brachial plexus may relieve phantom limb pain and unpleasant phantom feelings (cramping) for an extended period.

Preliminary Evidence for Training-Induced Changes of Morphology and Phantom Limb Pain

The aim of this study was to investigate whether a special prosthetic training in phantom limb pain patients aimed at increasing the functional use of the prosthesis leads to neural morphological plasticity of brain structures and a reduction in phantom limb pain. For chronic pain disorders, it was shown that morphological alterations due to pain might become at least partially reversed by pain therapies. Phantom limb pain is a chronic pain disorder that is frequently followed by neural plasticity of anatomical brain structures. In our study, 10 patients with amputation of the upper limb participated in a two-week training with a myoelectric prosthesis with somatosensory feedback. Grip strength was fed back with electrocutaneous stimulus patterns applied to the stump. Phantom limb pain was assessed before and after the two-week training. Similarly, two T1 weighted MRI scans were conducted for longitudinal thickness analyses of cortical brain structures. As result of this treatment, patients experienced a reduction in phantom limb pain and a gain in prosthesis functionality. Furthermore, we found a change of cortical thickness in small brain areas in the visual stream and the post-central gyrus ipsilateral to the amputation indicating morphological alterations in brain areas involved in vision and pain processing.

Human Brain Stem Structures Respond Differentially to Noxious Heat

Concerning the physiological correlates of pain, the brain stem is considered to be one core region that is activated by noxious input. In animal studies, different slopes of skin heating (SSH) with noxious heat led to activation in different columns of the midbrain periaqueductal gray (PAG). The present study aimed at finding a method for differentiating structures in PAG and other brain stem structures, which are associated with different qualities of pain in humans according to the structures that were associated with different behavioral significances to noxious thermal stimulation in animals. Brain activity was studied by functional MRI in healthy subjects in response to steep and shallow SSH with noxious heat. We found differential activation to different SSH in the PAG and the rostral ventromedial medulla (RVM). In a second experiment, we demonstrate that the different SSH were associated with different pain qualities. Our experiments provide evidence that brainstem structures, i.e., the PAG and the RVM, become differentially activated by different SSH. Therefore, different SSH can be utilized when brain stem structures are investigated and when it is aimed to activate these structures differentially. Moreover, percepts of first pain were elicited by shallow SSH whereas percepts of second pain were elicited by steep SSH. The stronger activation of these brain stem structures to SSH, eliciting percepts of second vs. first pain, might be of relevance for activating different coping strategies in response to the noxious input with the two types of SSH.

Enhanced Brain Responses to Pain-Related Words in Chronic Back Pain Patients and Their Modulation by Current Pain

Previous functional magnetic resonance imaging (fMRI) studies in healthy controls (HC) and pain-free migraine patients found activations to pain-related words in brain regions known to be activated while subjects experience pain. The aim of the present study was to identify neural activations induced by pain-related words in a sample of chronic back pain (CBP) patients experiencing current chronic pain compared to HC. In particular, we were interested in how current pain influences brain activations induced by pain-related adjectives. Subjects viewed pain-related, negative, positive, and neutral words; subjects were asked to generate mental images related to these words during fMRI scanning. Brain activation was compared between CBP patients and HC in response to the different word categories and examined in relation to current pain in CBP patients. Pain-related words vs. neutral words activated a network of brain regions including cingulate cortex and insula in subjects and patients. There was stronger activation in medial and dorsolateral prefrontal cortex (DLPFC) and anterior midcingulate cortex in CPB patients than in HC. The magnitude of activation for pain-related vs. negative words showed a negative linear relationship to CBP patients’ current pain. Our findings confirm earlier observations showing that pain-related words activate brain networks similar to noxious stimulation. Importantly, CBP patients show even stronger activation of these structures while merely processing pain-related words. Current pain directly influences on this activation.

Persistierende Schmerzen und kortikale Reorganisation nach Makroreplantationen der oberen Extremität

Hintergrund. Die chirurgische Wiederangliederung traumatisch amputierter Körperteile ist dank ausgereifter mikrochirurgischer Techniken inzwischen nicht mehr nur eine wertvolle Alternative zur Stumpfversorgung und Prothesenanpassung. In den Fällen, in denen Replantationen möglich sind, sind sie vielmehr alsGoldstandard anzusehen, da zahlreiche negative Konsequenzen von Amputationen, wie Phantomschmerzen im amputierten Körperteil [7, 15, 19, 20] oder Angst und Depressionen [12], vermieden oder reduziert werden. Zudem sind auch das funktionelle Ergebnis und diewiedererlangte Sensibilität nach einer Replantation der Prothese gleichwertig oderüberlegen [11].DieseVorteile rechtfertigen die Wahl, die Körperintegrität durch Replantation zu erhalten, da eine erhöhte Lebensqualität damit einhergeht [9, 11]. Dennoch bleiben auch bei Makroreplantationen Probleme. So ist ein Teil der Replantationspatienten von persistierenden Schmerzen betroffen [23]. Auch das sensorische und funktionelle Ergebnis von Replantationen hat sich in den vergangenen Jahrzehnten nicht im gleichen Maße verbessert, wie sich die mikrochirurgischen Verfahren weiterentwickelt haben [14]. So bleibt die funktionelle Wiederherstellung nach Makroreplantationen, der eine Amputation proximal des Radiokarpalgelenks vorausgeht, eine große Herausforderung [12]. Eine mögliche Ursache dafür sind die zahlreichen Veränderungen, die sowohl eine Amputation als auch eine Replantation im peripheren Nervensystem und im Kortex bewirkt. Bislang gibt es nur wenige Studien zu den Veränderungen in der homunkulären Organisation in den somatosensorischen Kortizes, die sowohl durch die Replantation als auch durch die potenzielle und allmählich verlaufende Reinnervierung angestoßen werden [1, 3]. Die bisherigen Ergebnisse deuten jedoch darauf hin, dass periphere Mechanismen allein die nicht zufriedenstellende Wiederherstellung der Sensibilität und der Funktionalität des Replantats sowie die persistierenden Schmerzen nicht ausreichend erklären können. Ziel dieser Studie war es, zentrale Prozesse im Sinn kortikaler Plastizität nach Makroreplantationen und deren Zusammenhang mit persistierenden Schmerzen zu untersuchen.

Leg Prosthesis With Somatosensory Feedback Reduces Phantom Limb Pain and Increases Functionality

Phantom limb pain (PLP) develops in most patients with lower limb amputation. Changes in the peripheral and central nervous system (CNS) are hypothesized to contribute to PLP. Based on ideas to modify neural reorganization within the CNS, the aim of the study was to test, whether prostheses with somatosensory feedback might help to reduce PLP, and increase the functionality of movement with a prosthesis. We therefore equipped the prostheses of 14 lower leg amputees with a simple to use feedback system that provides electrocutaneous feedback to patients’ thigh whenever the foot and toes of the prosthesis touch the ground. Two weeks of training with such a feedback prosthesis reduced PLP, increased the functional use of the prosthesis, and increased patients’ satisfaction with prosthesis use. We found a significant overall reduction of PLP during the course of the training period. Most patients reported lower PLP intensities at the end of the day while before training they have usually experienced maximal PLP intensities. Furthermore, patients also reported larger walking distances and more stable walking and better posture control while walking on and across a bumpy or soft ground. After training, the majority of participants (9/14) preferred such a feedback system over no feedback. This study extends former observations of a similar training procedure with arm amputees who used a similar feedback training to improve the functionality of an arm prosthesis in manipulating and grasping objects.