Quantitative assessment of proprioceptive dysfunction in cancer survivors post oxaliplatin-containing chemotherapy

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Background: Oxaliplatin (OX) is commonly used for gastrointestinal cancers but can cause chronic neurotoxicity with long-term motor impairments (e.g. dexterity loss, poor balance, and falls). These impairments are often attributed to OX-induced sensory neuropathy that disrupts touch, vibration, and proprioception in distal limbs. However, some cancer survivors report motor impairments even in the absence of sensory neuropathy. Recent animal studies suggest OX induces global signaling dysfunction in muscle proprioceptors that may account for the motor impairments in the absence of sensory neuropathy. However, this mechanism has yet to be investigated in cancer survivors. We hypothesize that cancer survivors will display impaired proprioceptive function compared to age-matched healthy controls using quantitative techniques that are more sensitive than current clinical measures. Methods: We assessed use of proprioception for controlling upper extremity position, force, and posture using target reaching, force matching, and postural stability tasks, respectively. A haptic robot quantified motor performance in all tasks, performed with and without visual feedback to disambiguate proprioceptive from vision. The dominant hand and wrist were fixed in an orthosis emphasizing elbow and shoulder use since these joints are less likely to have sensory neuropathy. Self-reported symptoms and functional limitations were measured with the QLQ-CIPN20 questionnaire. Accuracy and trial-to-trial variability for each task were compared between cancer survivors and controls using linear mixed effect models. Results: Thirteen cancer survivors (0 – 20 months post OX-treatment) and 7 controls completed the study. Without visual feedback, cancer survivors had significantly decreased accuracy (p < 0.001) and increased trial-to-trial variability (p < 0.05) in all tasks compared to controls. Deficits in force matching were correlated with self-reported motor dysfunction on the QLQ-CIPN20 (r = 0.87, p < 0.001). Conclusions: Proprioceptive deficits occur in cancer survivors who received OX-treatment and are associated with motor dysfunction. This identified mechanism of motor impairment may present opportunities for targeted interventions.

Cancer's role in chemotherapy-induced neuropathy

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Background: For the constellation of neurological disorders known as chemotherapy-induced neuropathy, mechanistic understanding, and treatment remain deficient. This might be due to the fact that studies on the effects of chemotherapies on the nervous system have utilized experimental models that exclude cancer perhaps due to the presumption that chemotherapy alone explains the neuropathology. However, the convergence of cancer and chemotherapy on the same biological processes seems likely to yield non-linear interactions. This led us to hypothesize that clinically relevant neuropathy emerges from codependent actions of cancer and chemotherapy. Methods: We established a clinically-relevant animal model of chronic sensory neuropathy in rats with cancer (adenomatous polyposis coli in rat colon: Apc+/Pirc) and age-matched animals without cancer ( ApcWT) that were randomly assigned to receive a human-scaled course of oxaliplatin (OX) or control treatment (4 groups). We quantified behavioral deficits during precision ladder walking, a validated measure of locomotor performance. Neuronal signaling was measured during terminal in vivo experiments to examine the response of sensory neurons to physiologically-relevant stimuli. We defined statistical significance as when 95% of a highest density interval (HDI) of posterior probabilities do not overlap (hierarchical Bayesian modeling). Results: Apc+/Pirc+OX (n = 11) rats exhibited significantly higher error rate (19.2±5.6%, 95%HDI) during precision ladder walking in comparison to ApcWT+control (2.4±2.7%: n = 9) or Apc+/Pirc +control (2.5±2.9%: n = 7) and significantly exceeded the error rate observed in animals treated with OX alone (8.4±3.1%: n = 10). In contrast to the observations in all other groups, we found drastically impaired neuronal signaling in Apc+/Pirc+OX rats which manifested as significantly reduced sensitivity and attenuated static and dynamic firing patterns (95%HDI). Conclusions: We present the first evidence that chronic neuropathy cannot be explained by the effects of chemotherapy alone but instead depend on non-linear interactions between cancer and chemotherapy. This understanding is a prerequisite for developing meaningful treatment or prevention of neuropathy.

Chemotherapy-induced neuronal dysfunction in the absence of axon degeneration

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Background: Colorectal cancer is one of the three most prevalent cancers. Mortality rates have largely decreased due, in part, to advanced treatments such as platinum-based chemotherapy (e.g. oxaliplatin – OX). Unfortunately, OX induces severe off-target, neurotoxic side-effects in the sensory nervous system that can limit or end treatment and diminish patient quality of life for years. Patient symptoms are often attributed to dying-back degeneration of primary sensory axons despite the absence of conclusive evidence. We tested the hypothesis that proprioceptive disorders persisting after chemotherapy result solely from axon degeneration of muscle proprioceptors. Methods: We used a rat model to test our hypothesis. In a rodent model of OX clinical cancer treatment, one that exhibits sensorimotor deficits in a test of proprioceptive behavior, we performed single-neuron in vivo electrophysiological and immunohistological experiments. We then profiled transcriptomes of sensory neurons to gain unbiased insight into molecular evidence of degeneration. We compared the OX group of rats (n = 18) to healthy, control rats (n = 6) using hierarchical Bayesian analysis. Results: We found no evidence for sensory axon degeneration in electrophysiologic measures of axon conduction or in immunohistochemical analysis of the axon terminals of sensory neurons, OX and control rats were indistinguishable by these measures. Unbiased transcriptional profiling gave little evidence of neuronal degeneration, although genes related to axon transport showed signs of dysregulation. Structural degeneration was also ruled out by finding that all sensory neurons fired in response to stretch. Nonetheless, anomalous firing patterns were observed, e.g. decreased spike activity in response to mechanosensory stimulation, consistent with changes in ion channel physiology. Conclusions: Our findings reject the hypothesis that nerve degeneration is required to explain OX-related sensorimotor disorders. Our research suggests biological mechanisms that are alternative to axon degeneration in explaining sensorimotor changes due to OX.

Increasing Access to Cost Effective Home-Based Rehabilitation for Rural Veteran Stroke Survivors

INTRODUCTION

An estimated 750,000 Americans experience a stroke annually. Most stroke survivors require rehabilitation. Limited access to rehabilitation facilities has a pronounced burden on functional outcomes and quality of life. Robotic devices deliver reproducible therapy without the need for real-time human oversight. This study examined the efficacy of using home-based, telerobotic-assisted devices (Hand and Foot Mentor: HM and FM) to improve functional ability and reduce depression symptoms, while improving access and cost savings associated with rehabilitation.

METHODS

Twenty stroke survivors performed three months of home-based rehabilitation using a robotic device, while a therapist remotely monitored progress. Baseline and end of treatment function and depression symptoms were assessed. Satisfaction with the device and access to therapy were determined using qualitative surveys. Cost analysis was performed to compare home-based, robotic-assisted therapy to clinic-based physical therapy.

RESULTS

Compared to baseline, significant improvement in upper extremity function (30.06%, p= 0.046), clinically significant benefits in gait speed (29.03%), moderate improvement in depressive symptoms (28.44%) and modest improvement in distance walked (30.2%) were observed. Participants indicated satisfaction with the device. Home-based robot therapy expanded access to post-stroke rehabilitation for 35% of the people no longer receiving formal services and increased daily access for the remaining 65%, with a cost savings of $2,352 (64.97%) compared to clinic-based therapy.

CONCLUSION

Stroke survivors made significant clinically meaningful improvements in the use of their impaired extremities using a robotic device in the home. Home-based, robotic therapy reduced costs, while expanding access to a rehabilitation modality for people who would not otherwise have received care.