Sensory neuropathies including painful and toxic neuropathies

Essential References for Structural Analysis of the Peripheral Nervous System for Pathologists and Toxicologists

Toxicologic neuropathology for the peripheral nervous system (PNS) is a vital but often underappreciated element of basic translational research and safety assessment. Evaluation of the PNS may be complicated by unfamiliarity with normal nerve and ganglion biology, which differs to some degree among species; the presence of confounding artifacts related to suboptimal sampling and processing; and limited experience with differentiating such artifacts from genuine disease manifestations and incidental background changes. This compilation of key PNS neurobiology, neuropathology, and neurotoxicology references is designed to allow pathologists and toxicologists to readily access essential information that is needed to enhance their proficiency in evaluating and interpreting toxic changes in PNS tissues from many species.

Orofacial Pain in Cancer: Part I—Mechanisms

The mechanisms involved, and possible treatment targets, in orofacial pain due to cancer are poorly understood. The aim of the first of this two-part series is to review the involved pathophysiological mechanisms and explore their possible roles in the orofacial region. However, there is a lack of relevant research in the trigeminal region, and we have therefore applied data accumulated from experiments on cancer pain mechanisms in rodent spinal models. In the second part, we review the clinical presentation of cancer-associated orofacial pain at various stages: initial diagnosis, during therapy (chemo-, radiotherapy, surgery), and in the post-therapy period. In the present article, we provide a brief outline of trigeminal functional neuro-anatomy and pain-modulatory pathways. Tissue destruction by invasive tumors (or metastases) induces inflammation and nerve damage, with attendant acute pain. In some cases, chronic pain, involving inflammatory and neuropathic mechanisms, may ensue. Distant, painful effects of tumors include paraneoplastic neuropathic syndromes and effects secondary to the release of factors by the tumor (growth factors, cytokines, and enzymes). Additionally, pain is frequent in cancer management protocols (surgery, chemotherapy, and radiotherapy). Understanding the mechanisms involved in cancer-related orofacial pain will enhance patient management.

Neurotrimin is an estrogen-regulated determinant of peripheral sympathetic innervation

Mechanisms underlying axon degeneration in peripheral neuropathies and during normal remodeling are poorly understood. Because estrogen induces widespread sympathetic axon degeneration in female reproductive tract smooth muscle, we surveyed estrogen-regulated genes in rat myometrium. Microarray analysis revealed that the neural cell adhesion protein neurotrimin (Ntm) was markedly up-regulated 6 hr and down-regulated 24 hr after injection of 17beta-estradiol, and real time RT-PCR confirmed this pattern of expression. Protein analysis by Western blotting showed that uterine Ntm protein is also up-regulated in vivo 6-24 hr following estrogen injection and that Ntm protein is increased selectively in the myometrium during the high-estrogen phase of the estrous cycle. Cultured myometrial smooth muscle cells display perinuclear accumulations of Ntm protein, and 17beta-estradiol also increases intracellular levels of Ntm and its secretion into the culture medium. To determine if neurotrimin is required for estrogen-induced sympathetic pruning, sympathetic neurons were cocultured with uterine smooth muscle cells transfected with siRNA directed against Ntm. Although estrogen inhibited neurite outgrowth in nontransfected cocultures, estrogen's ability to reduce sympathetic outgrowth was impaired substantially following Ntm down-regulation. This supports a role for neurotrimin in mediating estrogen-induced sympathetic pruning in some peripheral targets. Together with earlier studies, these findings support the idea that physiological sympathetic axon degeneration is a multifactorial process requiring dynamic regulation of multiple repellant proteins.

[The diagnosis of acquired sensory neuropathies]

INTRODUCTION

Peripheral neuropathies usually include a sensory component of various causes. The diagnosis approach requires careful a clinical assessment and a precise electrophysiological exploration.

STATE OF ART

Axonal sensory polyneuropathies are classified according to the type of fibers involved (large or small fibers). While there is a large number of causes, current emphasis is placed on glucose intolerance as a source of small-fiber sensory neuropathies. Demyelinating polyneuropathies are often associated with a monoclonal IgM gammapathy with anti-MAG activity. Multiple sensory mononeuropathies are exceptional and suggest possible early-phase vasculities, sensorymotor neuropathy with conduction blocks or leprosy. Sensory neuronopathies can also suggest Sjögren's syndrome or a paraneoplastic syndrome. Finally chronic sensory polyradiculoneuritis constitute a rare subgroup clearly defined as demyelinating inflammatory neuropathy.

CONCLUSION

The diagnostic approach to sensory neuropathies requires careful nosological electroclinical classification to reduce the number of explorations performed for etiological diagnosis.

A New Animal Model of Vincristine-Induced Nociceptive Peripheral Neuropathy

Using doses close to those used clinically, we have developed an animal model of vincristine-induced nociceptive sensory neuropathy after repeated intravenous injection in male Sprague-Dawley rats. In order to validate the model, three different doses (50, 100 and 150 microg/kg) of vincristine were injected every 2nd day until five injections had been given. The sensory behavioural assessment revealed mechanical hyperalgesia and allodynia associated with cold thermal hyperalgesia and allodynia. With regard to electrophysiological evaluation, we observed a decrease in the nerve conduction velocity in the highest dose group. Morphological studies revealed few degenerated fibers in the sciatic nerve and many degenerated myelinated axons in the fine nerve fibers of the subcutaneous paw tissue. Finally, to develop an animal model, we chose the 150 microg/kg dose because of the good general clinical status of the rats without motor function changes associated with severe sensation disorders like hyperalgesia and allodynia. This model of vincristine-induced painful neuropathy will be used to explore physiopathological mechanisms implied in the genesis of neuropathic pain and also to test new analgesic and neuroprotective drugs.

Neurophysiological Diagnosis of Acquired Sensory Ganglionopathies

We examined 29 patients with chronic progressive ganglionopathy of different etiology. Neurophysiological abnormalities were dominated by a widespread decrease in sensory nerve action potential amplitudes, which involved both upper and lower limb nerves, even in patients with asymmetrical or patchy clinical presentation. This impairment of sensory nerve conduction, reflecting a nonlenght-dependent pattern of peripheral axon degeneration, should be considered the hallmark of ganglionopathies. The evidence of central sensory pathway impairment, which allows to localize the pathology to the dorsal root ganglion neurons, could be better confirmed by cervical magnetic resonance imaging, which showed a diffuse hyperintensity in the posterior columns in all patients, than by somatosensory evoked potentials, which were undetectable in most of the patients. Few patients showed an impairment of individual motor nerves, which appeared more severe in paraneoplastic associated ganglionopathies. Neurophysiological abnormalities did not appear significantly changed at the 4-year follow-up. We emphasize that distinct abnormalities allow to differentiate ganglionopathies from axonal sensory neuropathies on routine neurophysiological examination.

Evidence for an antihyperalgesic effect of venlafaxine in vincristine-induced neuropathy in rat

Venlafaxine, a new antidepressant with fewer side effects, could be of interest to reduce neuropathic pain following antineoplasic drug treatment. In the present study, we demonstrated that venlafaxine inhibits hyperalgesia in a new rat model of neuropathy induced by the antineoplasic drug vincristine, and exerts its effect preferentially via supraspinal and spinal mechanisms.

Chemotherapy-induced peripheral neuropathy

While cancer remains an important public health concern, novel and enhanced treatment modalities have increased the length of survival of individuals diagnosed with the disease. The treatment of most cancers requires the use of chemotherapeutic agents to affect cure, maintain control of the disease, or provide palliation of symptoms. Although the use of chemotherapeutic agents can serve to prolong life, such agents are associated with significant side effects. Increasing clinical evidence suggests treatment of cancer with neurotoxic agents results in some degree of peripheral neuropathy. Specific drug categories implicated in the development of peripheral neuropathy are the plant alkaloids, interferons, antimitotics, taxanes, and platinum-based compounds. Drug-induced peripheral neuropathy is sensory, dose-related and cumulative and is usually delayed, appearing weeks after initiation of therapy. The number of individuals at risk for the development of chemotherapy-induced neuropathy is expected to increase proportionately with clinical protocols utilizing higher or more frequent dosing. As advanced cancer treatments and clinical trials can result in extending the lives of individuals affected by cancer, long-term functional deficits resulting from life-saving treatments must now be addressed. As such, peripheral neuropathy has emerged as an important consequence of cancer therapy.

Diagnostic investigation of patients with chronic polyneuropathy: evaluation of a clinical guideline

OBJECTIVE

(1) To evaluate a clinical guideline for the diagnostic investigation of patients presenting with signs and symptoms (present for longer than 6 weeks) suggesting a chronic polyneuropathy. (2) To investigate the contribution of electrophysiological studies to a focused search for aetiology in these patients.

METHODS

A chart review was carried out of a consecutive group of outpatients in 1993-7 at a university department of neurology, with signs and symptoms suggesting a polyneuropathy in whom the diagnostic investigation had been carried out according to a recently introduced guideline. Diagnostic tests were performed and final diagnoses were made.

RESULTS

Unnecessary investigations were carried out in 108 (51%) of 213 patients and too few tests in 23 (11%) of these patients. In 82 (48%) of the 172 patients who fulfilled the inclusion criteria neurophysiological tests did not contribute to the final diagnosis. Neurophysiological criteria for demyelination were fulfilled in only 13 (8%) of the 172 patients.

CONCLUSION

In patients presenting with signs and symptoms of chronic polyneuropathy the number of tests in the diagnostic investigation can be considerably reduced. In patients with signs and symptoms of polyneuropathy, providing the clinical phenotype is typical, in the presence of diabetes mellitus, renal failure, HIV infection, alcoholism, or use of potentially neurotoxic drugs further investigations are non-contributory. The significance of electrophysiological studies in the investigation of patients with polyneuropathy is rather to separate sensorimotor neuropathies from pure sensory neuropathies than to distinguish between demyelinating and axonal neuropathies.

Description of a short-term Taxol-induced nociceptive neuropathy in rats

This work describes a new animal model of neuropathic pain produced by the single intraperitoneal administration of Taxol (32 mg/kg) to male Sprague-Dawley rats. During the course of the experiment, the clinical status of the rats remained satisfactory and motor function was not altered. A number of classical behavioural tests of nociception as well as histological and electrophysiological investigations were performed. Taxol administration produced an important and rapidly developing mechanical hyperalgesia, a thermal hypoalgesia but no mechanical or thermal allodynia. Degenerative changes were observed in the sciatic nerve, the nerve fibres in the paw subcutaneous tissue and in the lumbar spinal cord. When Taxol or vehicle (a mix of Cremophor and ethanol) were repeatedly injected once a week for 5 weeks, similar nociceptive disorders were observed in addition to a decrease in peripheral nerve conduction velocity. The selective dysfunction of high-diameter myelinated fibres observed after one single administration of Taxol (32 mg/kg) may be attributable to paclitaxel-induced neuropathy, however other mechanisms causing neurochemical dysfunction must also be involved.

Emerging cell and molecular strategies for the study and treatment of painful peripheral neuropathies

Pharmacologic treatment for the symptoms of painful neuropathy has been problematic, because there has been limited understanding of the underlying etiologies and systemic levels that an effective dose can have on multiple side effects. The use of molecular methods, such as gene deletion from knockout mice and cellular minipumps for delivery of biologic antinociceptive molecules, has led to a better understanding of the underlying mechanisms of the induction of intractable neuropathic pain. The initiation of an excitatory cascade after injury or disease leads to the induction of various second messenger systems, loss or down-regulation of the endogenous inhibitory spinal GABA system and central sensitization, causing such pain. The development and use of cellular minipumps, immortalized cell lines bioengineered to secrete various antinociceptive molecules for the reversal of neuropathic pain, makes cellular therapy a strategy for clinical use in the next few years. The development of molecular "disimmortalization" technologies will make the use of such engineered cell lines safe for human use. Direct somatic gene transfer for neuropathic pain will eventually overcome the problems associated with transplantation of non-autologous and xenogenic cells. These virus-mediated methods, although at the early stages of evolution and use, offer large-scale production of biologic agents that can be conveniently and confidently used for the long-term relief of chronic neuropathic pain in a clinical setting, without systemic effects or surgical interventions.

Diagnostic work-up in peripheral neuropathy: an analysis of 171 cases

This study was set up to evaluate retrospectively the efficacy of a standard diagnostic procedure, including non-invasive and invasive (spinal tap, nerve/muscle biopsy) investigations, in the diagnosis of peripheral neuropathy. The medical records of 171 in-patients with the final diagnosis of peripheral neuropathy of determined or undetermined cause were reviewed and each individual diagnostic work-up was analysed. Basic investigations included the patient's history, a clinical examination and basic laboratory tests. Depending on the individual presentation, course, and severity, further non-invasive and invasive examinations were added according to the department's standard diagnostic procedure. The aetiology could be clarified in 124 patients (73%) and remained unclear in 47 cases. Excluding cases with acute and chronic inflammatory polyneuropathy (n=14), the number of idiopathic peripheral neuropathies dropped to 33. Non-invasive investigations were sufficient to reveal the underlying aetiology in 114 cases (83 %). It is concluded that, with the application of a standard procedure for the diagnosis of peripheral neuropathy, the aetiology can be clarified in 81% of patients. In the other 19% of patients the aetiology remains idiopathic. In the majority of cases, non-invasive investigations were sufficient for diagnosis.