Nervous system involvement after infection with COVID-19 and other coronaviruses

Viral infections have detrimental impacts on neurological functions, and even to cause severe neurological damage. Very recently, coronaviruses (CoV), especially severe acute respiratory syndrome CoV 2 (SARS-CoV-2), exhibit neurotropic properties and may also cause neurological diseases. It is reported that CoV can be found in the brain or cerebrospinal fluid. The pathobiology of these neuroinvasive viruses is still incompletely known, and it is therefore important to explore the impact of CoV infections on the nervous system. Here, we review the research into neurological complications in CoV infections and the possible mechanisms of damage to the nervous system.

Pathobiology of neuropathic pain

This review deals with physiological and biological mechanisms of neuropathic pain, that is, pain induced by injury or disease of the nervous system. Animal models of neuropathic pain mostly use injury to a peripheral nerve, therefore, our focus is on results from nerve injury models. To make sure that the nerve injury models are related to pain, the behavior was assessed of animals following nerve injury, i.e. partial/total nerve transection/ligation or chronic nerve constriction. The following behaviors observed in such animals are considered to indicate pain: (a) autotomy, i.e. self-attack, assessed by counting the number of wounds implied, (b) hyperalgesia, i.e. strong withdrawal responses to a moderate heat stimulus, (c) allodynia, i.e. withdrawal in response to non-noxious tactile or cold stimuli. These behavioral parameters have been exploited to study the pharmacology and modulation of neuropathic pain. Nerve fibers develop abnormal ectopic excitability at or near the site of nerve injury. The mechanisms include unusual distributions of Na(+) channels, as well as abnormal responses to endogenous pain producing substances and cytokines such as tumor necrosis factor alpha (TNF-alpha). Persistent abnormal excitability of sensory nerve endings in a neuroma is considered a mechanism of stump pain after amputation. Any local nerve injury tends to spread to distant parts of the peripheral and central nervous system. This includes erratic mechano-sensitivity along the injured nerve including the cell bodies in the dorsal root ganglion (DRG) as well as ongoing activity in the dorsal horn. The spread of pathophysiology includes upregulation of nitric oxide synthase (NOS) in axotomized neurons, deafferentation hypersensitivity of spinal neurons following afferent cell death, long-term potentiation (LTP) of spinal synaptic transmission and attenuation of central pain inhibitory mechanisms. In particular, the efficacy of opioids at the spinal level is much decreased following nerve injury. Repeated or prolonged noxious stimulation and the persistent abnormal input following nerve injury activate a number of intracellular second messenger systems, implying phosphorylation by protein kinases, particularly protein kinase C (PKC). Intracellular signal cascades result in immediate early gene (IEG) induction which is considered as the overture of a widespread change in protein synthesis, a general basis for nervous system plasticity. Although these processes of increasing nervous system excitability may be considered as a strategy to compensate functional deficits following nerve injury, its by-product is widespread nervous system sensitization resulting in pain and hyperalgesia. An important sequela of nerve injury and other nervous system diseases such as virus attack is apoptosis of neurons in the peripheral and central nervous system. Apoptosis seems to induce neuronal sensitization and loss of inhibitory systems, and these irreversible processes might be in common to nervous system damage by brain trauma or ischemia as well as neuropathic pain. The cellular pathobiology including apoptosis suggests future strategies against neuropathic pain that emphasize preventive aspects.

EFNS guidelines on pharmacological treatment of neuropathic pain

Neuropathic pain treatment remains unsatisfactory despite a substantial increase in the number of trials. This EFNS Task Force aimed at evaluating the existing evidence about the pharmacological treatment of neuropathic pain. Studies were identified using first the Cochrane Database then Medline. Trials were classified according to the aetiological condition. All class I and II controlled trials (according to EFNS classification of evidence) were assessed, but lower-class studies were considered in conditions that had no top level studies. Only treatments feasible in an outpatient setting were evaluated. Effects on pain symptoms/signs, quality of life and comorbidities were particularly searched for. Most of the randomized controlled trials included patients with postherpetic neuralgia (PHN) and painful polyneuropathies (PPN) mainly caused by diabetes. These trials provide level A evidence for the efficacy of tricyclic antidepressants, gabapentin, pregabalin and opioids, with a large number of class I trials, followed by topical lidocaine (in PHN) and the newer antidepressants venlafaxine and duloxetine (in PPN). A small number of controlled trials were performed in central pain, trigeminal neuralgia, other peripheral neuropathic pain states and multiple-aetiology neuropathic pains. The main peripheral pain conditions respond similarly well to tricyclic antidepressants, gabapentin, and pregabalin, but some conditions, such as HIV-associated polyneuropathy, are more refractory. There are too few studies on central pain, combination therapy, and head-to-head comparison. For future trials, we recommend to assess quality of life and pain symptoms or signs with standardized tools.

Insulin therapy protects the central and peripheral nervous system of intensive care patients

OBJECTIVE

To investigate the effectiveness of maintaining blood glucose levels below 6.1 mmol/L with insulin as prevention of secondary injury to the central and peripheral nervous systems of intensive care patients.

METHODS

The authors studied the effect of intensive insulin therapy on critical illness polyneuropathy (CIPNP), assessed by weekly EMG screening, and its impact on mechanical ventilation dependency, as a prospectively planned subanalysis of a large randomized, controlled trial of 1,548 intensive care patients. In the 63 patients admitted with isolated brain injury, the authors studied the impact of insulin therapy on intracranial pressure, diabetes insipidus, seizures, and long-term rehabilitation at 6 and 12 months follow-up.

RESULTS

Intensive insulin therapy reduced ventilation dependency (p = 0.0007; Mantel-Cox log rank test) and the risk of CIPNP (p < 0.0001). The risk of CIPNP among the 405 long-stay (> or =7 days in intensive care unit) patients was lowered by 49% (p < 0.0001). Of all metabolic and clinical effects of insulin therapy, and corrected for known risk factors, the level of glycemic control independently explained this benefit (OR for CIPNP 1.26 [1.09 to 1.46] per mmol blood glucose, p = 0.002). In turn, prevention of CIPNP explained the ability of intensive insulin therapy to reduce the risk of prolonged mechanical ventilation (OR 3.75 [1.49 to 9.39], p = 0.005). In isolated brain injury patients, intensive insulin therapy reduced mean (p = 0.003) and maximal (p < 0.0001) intracranial pressure while identical cerebral perfusion pressures were obtained with eightfold less vasopressors (p = 0.01). Seizures (p < 0.0001) and diabetes insipidus (p = 0.06) occurred less frequently. At 12 months follow-up, more brain-injured survivors in the intensive insulin group were able to care for most of their own needs (p = 0.05).

CONCLUSIONS

Preventing even moderate hyperglycemia with insulin during intensive care protected the central and peripheral nervous systems, with clinical consequences such as shortening of intensive care dependency and possibly better long-term rehabilitation.

Early and progressive sensorimotor anomalies in mice overexpressing wild-type human alpha-synuclein

Accumulation of alpha-synuclein in brain is a hallmark of synucleinopathies, neurodegenerative diseases that include Parkinson's disease. Mice overexpressing alpha-synuclein under the Thy-1 promoter (ASO) show abnormal accumulation of alpha-synuclein in cortical and subcortical regions of the brain, including the substantia nigra. We examined the motor deficits in ASO mice with a battery of sensorimotor tests that are sensitive to alterations in the nigrostriatal dopaminergic system. Male wild-type and ASO mice were tested every 2 months for 8 months for motor performance and coordination on a challenging beam, inverted grid, and pole, sensorimotor deficits in an adhesive removal test, spontaneous activity in a cylinder, and gait. Fine motor skills were assessed by the ability to grasp cotton from a bin. ASO mice displayed significant impairments in motor performance and coordination and a reduction in spontaneous activity as early as 2 months of age. Motor performance and coordination impairments became progressively worse with age and sensorimotor deficits appeared at 6 months. Fine motor skills were altered at 4 months and worsened at 8 months. These data indicate that overexpression of alpha-synuclein induced an early and progressive behavioral phenotype that can be detected in multiple tests of sensorimotor function. These behavioral deficits provide a useful way to assess novel drug therapy in genetic models of synucleinopathies.

The Crow-Fukase syndrome: a study of 102 cases in Japan

Clinical manifestations of 102 cases with the Crow- Fukase syndrome (the syndrome of polyneuropathy, anasarca, skin changes, endocrinopathy, dysglobulinemia, and organomegaly), with or without myeloma, were reviewed. Fifty-six cases with myeloma consisted of 31 with osteosclerotic, 17 with mixed osteosclerotic and osteolytic, and 8 with osteolytic. Forty-six cases without myeloma consisted of 2 with extramedullary plasmacytoma, 33 with M protein alone, and 11 with polyclonal protein alone. There was no significant difference in incidence of the major clinical manifestations between the two groups with and without myeloma. They had a common characteristic histologic finding of the lymph node resembling that of Castleman's disease.

Standardised method of determining vibratory perception thresholds for diagnosis and screening in neurological investigation

Vibration threshold determinations were made by means of an electromagnetic vibrator at three sites (carpal, tibial, and tarsal), which were primarily selected for examining patients with polyneuropathy. Because of the vast variation demonstrated for both vibrator output and tissue damping, the thresholds were expressed in terms of amplitude of stimulator movement measured by means of an accelerometer, instead of applied voltage which is commonly used. Statistical analysis revealed a higher power of discimination for amplitude measurements at all three stimulus sites. Digital read-out gave the best statistical result and was also most practical. Reference values obtained from 110 healthy males, 10 to 74 years of age, were highly correlated with age for both upper and lower extremities. The variance of the vibration perception threshold was less than that of the disappearance threshold, and determination of the perception threshold alone may be sufficient in most cases.

Chronic relapsing polyneuritis

Clinical, electrophysiological and pathological findings in 23 patients with subacute and relapsing idiopathic demyelinating polyneuropathies are described. In 17 patients with relapsing polyneuropathy, the neurological illness was unaccompanied by any systemic disturbances. The term preferred for the neuropathy in this group of patients is chronic relapsing polyneuritis. The findings in this group suggest that the common form of this syndrome is due to a single disease entity. Chronic relapsing polyneuritis differs from acute idiopathic polyneuritis chiefly in regard to the rate of evolution and the severity of the initial episode of polyneuropathy. If these two polyneuropathies have the same pathogenesis, the factor which determines whether the disease is acute and self-limiting or chronically relapsing is often present at the time of onset of the disease. The relationship of chronic relapsing polyneuritis to relapsing hypertrophic polyneuropathy and progressive hypertrophic polyneuropathy is also discussed and it is concluded that these diseases may constitute a spectrum of pathogenetically related disorders. In chronic relapsing polyneuritis, as in other demyelinating polyneuropathies, a marked segmental reduction in axon diameter accompanies demyelination. This corresponds to a more than 50% reduction in the volume of the affected region of the axon and it is associated with increased packing of axoplasmic organelles and wrinkling of the axolemma. It is suggested that in the normal myelinated nerve fibre, the Schwann cell and myelin sheath maintain fluid locally within the axon.

Efficacy and safety of recombinant human nerve growth factor in patients with diabetic polyneuropathy: A randomized controlled trial. rhNGF Clinical Investigator Group

CONTEXT

Nerve growth factor is a neurotrophic factor that promotes the survival of small fiber sensory neurons and sympathetic neurons in the peripheral nervous system. Recombinant human nerve growth factor (rhNGF) has demonstrated efficacy as treatment for peripheral neuropathy in experimental models and phase 2 clinical trials.

OBJECTIVE

To evaluate the efficacy and safety of a 12-month regimen of rhNGF in patients with diabetic polyneuropathy.

DESIGN

Randomized, double-blind, placebo-controlled phase 3 trial conducted from July 1997 through May 1999.

SETTING

Eighty-four outpatient centers throughout the United States.

PATIENTS

A total of 1019 men and women aged 18 to 74 years with either type 1 or type 2 diabetes and a sensory polyneuropathy attributable to diabetes.

INTERVENTIONS

Patients were randomly assigned to receive either rhNGF, 0.1 microg/kg (n = 504), or placebo (n = 515) by subcutaneous injection 3 times per week for 48 weeks. Patients were assessed at baseline, 12 weeks, 24 weeks, and 48 weeks.

MAIN OUTCOME MEASURES

The primary outcome measure was a change in neuropathy between baseline and week 48, demonstrated by the Neuropathy Impairment Score for the Lower Limbs, compared between the 2 groups. Secondary outcome measures included quantitative sensory tests using the CASE IV System, the Neuropathy Symptom and Change questionnaire, the Patient Benefit Questionnaire (PBQ), and a global symptom assessment, as well as nerve conduction studies and occurrence of new plantar foot ulcers. Patients also were evaluated for presence of adverse events.

RESULTS

Among patients who received rhNGF, 418 (83%) completed the regimen compared with 461 (90%) who received placebo. Administration of rhNGF was safe, with few adverse events attributed to treatment apart from injection site pain/hyperalgesia and other pain syndromes. However, neither the primary end point (P =.25) nor most of the secondary end points demonstrated a significant benefit of rhNGF. Exceptions were the global symptom assessment (P =.03) and 2 of 32 comparisons within the PBQ, which showed a modest but significant benefit of rhNGF (P =.05 for severity of pain in the legs and P =.003 for 6-month symptoms in the feet and legs).

CONCLUSION

Unlike previous phase 2 trials, this phase 3 clinical trial failed to demonstrate a significant beneficial effect of rhNGF on diabetic polyneuropathy. JAMA. 2000;284:2215-2221.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Neuromuscular manifestations of critical illness

Critical illness, more precisely defined as the systemic inflammatory response syndrome (SIRS), occurs in 20%-50% of patients who have been on mechanical ventilation for more than 1 week in an intensive care unit. Critical illness polyneuropathy (CIP) and myopathy (CIM), singly or in combination, occur commonly in these patients and present as limb weakness and difficulty in weaning from the ventilator. Critical illness myopathy can be subdivided into thick-filament (myosin) loss, cachectic myopathy, acute rhabdomyolysis, and acute necrotizing myopathy of intensive care. SIRS is the predominant underlying factor in CIP and is likely a factor in CIM even though the effects of neuromuscular blocking agents and steroids predominate in CIM. Identification and characterization of the polyneuropathy and myopathy depend upon neurological examination, electrophysiological studies, measurement of serum creatine kinase, and, if features suggest a myopathy, muscle biopsy. The information is valuable in deciding treatment and prognosis.

The clinical picture of neuropathic pain

Neuropathic pains refer to a heterogeneous group of pain conditions characterised by lesion or dysfunction of the normal sensory pathways. Clinical characteristics include: delayed onset of pain after nervous system lesion, pain in area of sensory loss, spontaneous and different evoked types of pains. It has so far only been possible to classify these pains on basis of underlying cause or on anatomical location. The mechanisms underlying neuropathic pain are not yet clear, but neuronal hyperexcitability in those neurons that have lost their normal patterned input seems to be a common denominator for many, if not all types, of neuropathic pains. Along these lines, a mechanism-based classification has recently been proposed, which is an attractive approach because it provides a frame for a rationally based therapy of neuropathic pains. The clinical manifestations of neuronal hyperexcitability due to nervous system lesions is described.

Chronic inflammatory demyelinating polyneuropathy: clinical features and response to treatment in 67 consecutive patients with and without a monoclonal gammopathy

We report the clinical and EMG details of 67 consecutive patients with strictly defined chronic inflammatory demyelinating polyneuropathy (CIDP) during a 4-year period and compare responses to treatment in patients with idiopathic CIDP (CIDP-I) and CIDP with monoclonal gammopathy of uncertain significance (CIDP-MGUS). Patients were examined an average of 28 months after first symptoms. There were several variant presentations that still conformed to the clinical and electrophysiologic definitions of CIDP, including a pure motor syndrome (10%), sensory ataxic variant (12%), mononeuritis multiplex pattern (9%), paraparetic pattern (4%), and relapsing acute Guillain-Barré syndrome (16%). Pain was more frequent than in previous studies (42%). Conduction block was the commonest EMG abnormality (detected in at least one nerve in 73% of patients), but only 31% had a pure demyelinating neuropathy and the majority had some degree of axonal change. Patients with CIDP-MGUS had less severe weakness, greater imbalance, leg ataxia, vibration loss in the hands, and absent median and ulnar sensory potentials, but were as likely as CIDP-I patients to respond to plasma exchange. Seventeen of 44 patients (39%) with idiopathic CIDP improved for at least 2 months with an initial therapy. Although the response rates among plasma exchange, IVIG, and steroids were similar, functional improvement (Rankin score) was greatest with plasma exchange. Of 26 patients who failed to respond to an initial therapy, 9 (35%) benefited from an alternative treatment, and of the 11 who required a third modality 3 (27%) improved. Overall, 66% responded to one of the three main therapies for CIDP.

ICU-Acquired Weakness

Observational studies of patients receiving prolonged mechanical ventilation and other forms of critical care support have determined acquired neuromuscular disorders to be extremely common. Early studies used electrophysiologic investigations to diagnose critical illness polyneuropathy (CIP) and muscle biopsy to confirm critical illness myopathy (CIM). More recent approaches seek to obviate these invasive techniques and build on a standardized bedside neuromuscular examination to identify patients with acquired weakness syndromes. Serial examination in the alert patient may serve as a reasonable prognosticator for most patients. The importance of ICU-acquired weakness syndromes is supported by the observation that muscle wasting and weakness are among the most prominent long-term complications of survivors of ARDS. In addition, a strong association appears to exist between acquired weakness and protracted ventilator dependence, an important determinant of ICU length of stay. Multivariate analysis has identified several risk factors associated with increased incidence for ICU-acquired weakness, including severe systemic inflammation, medications (specifically, corticosteroids and neuromuscular blocking agents), glycemic control, and immobility. We advocate an approach to this common syndrome that identifies risk factors early in the hope of minimizing their impact.

Practice Parameter: evaluation of distal symmetric polyneuropathy: role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review) [RETIRED]. Report of the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Academy of Physical Medicine and Rehabilitation

BACKGROUND

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of autonomic testing, nerve biopsy, and skin biopsy for the assessment of polyneuropathy.

METHODS

A literature review using MEDLINE, EMBASE, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based upon the level of evidence.

RESULTS AND RECOMMENDATIONS

1) Autonomic testing should be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). 2) Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). 3) Skin biopsy is a validated technique for determining intraepidermal nerve fiber density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy.

The clinical and laboratory features of chronic sensory ataxic neuropathy with anti-disialosyl IgM antibodies

The clinical and laboratory phenotype of a paraproteinaemic neuropathy syndrome termed chronic sensory ataxic neuropathy with anti-disialosyl IgM antibodies is described in a series of 18 cases. Previous single case reports have outlined some features of this syndrome. All 18 cases were defined by the presence of serum IgM antibodies which react principally with NeuAc (alpha2-8)NeuAc(alpha2-3)Gal-configured disialosyl epitopes common to many gangliosides including GDlb, GD3, GTlb and GQlb. In 17 out of 18 cases, the serum contained benign IgM paraproteins, and in four of these cases at least two IgM paraproteins were present. The IgM antibodies were also cold agglutinins in 50% of cases. The clinical picture comprised a chronic neuropathy with marked sensory ataxia and areflexia, and with relatively preserved motor function in the limbs. In addition, 16 out of 18 cases had motor weakness affecting oculomotor and bulbar muscles as fixed or as relapsing-remitting features. When present in their entirety, these clinical features have been described previously under the acronym CANOMAD: chronic ataxic neuropathy, ophthalmoplegia, IgM paraprotein, cold agglutinins and disialosyl antibodies. This distribution of clinical features is reminiscent of Miller Fisher syndrome, in which acute-phase anti-disialylated ganglioside IgG antibodies are found. Clinical electrophysiology and nerve biopsy show both demyelinating and axonal features. A partial response to intravenous immunoglobulin and other treatments is reported in some cases.

Organophosphate-Induced Delayed Polyneuropathy

Organophosphate-induced delayed polyneuropathy (OPIDP) is a rare toxicity resulting from exposure to certain organophosphorus (OP) esters. It is characterised by distal degeneration of some axons of both the peripheral and central nervous systems occurring 1-4 weeks after single or short-term exposures. Cramping muscle pain in the lower limbs, distal numbness and paraesthesiae occur, followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. Signs include high-stepping gait associated with bilateral foot drop and, in severe cases, quadriplegia with foot and wrist drop as well as pyramidal signs. In time, there might be significant recovery of the peripheral nerve function but, depending on the degree of pyramidal involvement, spastic ataxia may be a permanent outcome of severe OPIDP. Human and experimental data indicate that recovery is usually complete in the young. At onset, the electrophysiological changes include reduced amplitude of the compound muscle potential, increased distal latencies and normal or slightly reduced nerve conduction velocities. The progression of the disease, usually over a few days, may lead to non-excitability of the nerve with electromyographical signs of denervation. Nerve biopsies have been performed in a few cases and showed axonal degeneration with secondary demyelination. Neuropathy target esterase (NTE) is thought to be the target of OPIDP initiation. The ratio of inhibitory powers for acetylcholinesterase and NTE represents the crucial guideline for the aetiological attribution of OP-induced peripheral neuropathy. In fact, pre-marketing toxicity testing in animals selects OP insecticides with cholinergic toxicity potential much higher than that to result in OPIDP. Therefore, OPIDP may develop only after very large exposures to insecticides, causing severe cholinergic toxicity. However, this was not the case with certain triaryl phosphates that were not used as insecticides but as hydraulic fluids, lubricants and plasticisers and do not result in cholinergic toxicity. Several thousand cases of OPIDP as a result of exposure to tri-ortho-cresyl phosphate have been reported, whereas the number of cases of OPIDP as a result of OP insecticide poisoning is much lower. In this article, we mainly discuss OP pesticide poisoning, particularly when caused by chlorpyrifos, dichlorvos, isofenphos, methamidophos, mipafox, trichlorfon, trichlornat, phosphamidon/mevinphos and by certain carbamates. We also discuss case reports where neuropathies were not convincingly attributed to fenthion, malathion, omethoate/dimethoate, parathion and merphos. Finally, several observational studies on long-term, low-level exposures to OPs that sometimes reported mild, inconsistent and unexplained changes of unclear significance in peripheral nerves are briefly discussed.

NPhys Trial Investigators, Albers JW, Andersen H, Bolton CF, England JD, Klein CJ, Llewelyn JG, Mauermann ML, Russell JW, Singer W, Smith AG, Tesfaye S, Vella A. Signs and symptoms versus nerve conduction studies to diagnose diabetic sensorimotor polyneuropathy: Cl vs. NPhys trial

The purpose was to test whether physicians can validly and reproducibly diagnose diabetic sensorimotor polyneuropathy (DSPN). Twelve physicians assessed 24 patients with diabetes mellitus (DM) on consecutive days (576 examinations) with physical features and voice disguised. Results were compared to gold standard 75% group diagnosis (dx) and a nerve conduction score (Sigma5 NC nds). Masking of patients was achieved. Reproducibility measured by the kappa coefficient and compared to Sigma5 NC nd varied considerably among physicians: median and ranges: signs 0.8 (0.32-1.0); symptoms 0.79 (0.36-1.0), and diagnoses 0.47 (0.33-0.84), both low and high scores indicating poor performance. There was substantial agreement between 75% group dx and confirmed NC abnormality (abn). As compared to Sigma5 NC, individual physicians' clinical dx was excessively variable and frequently inaccurate. Study physician dx from signs and symptoms were excessively variable, often overestimating DSPN. Specific approaches to improving clinical proficiency should be tested.

Ganglioside composition of the human cranial nerves, with special reference to pathophysiology of Miller Fisher syndrome

Total ganglioside fractions from the human cranial nerves purified on a Phenyl Sepharose column, were given mild alkaline treatment, after which their composition and amounts of lipid-bound sialic acid were determined by HPTLC-densitometry with resorcinol as the coloring reagent. The total amounts of lipid-bound sialic acid were 156.5 ng/mg of wet tissue in the Ist cranial nerve (olfactory tract) and 131.9 ng/mg in the IInd nerve, greater than the amounts in the other nerves (99.1-120.0 ng/mg). The Ist, IInd, and VIIIth nerves had GM4, but not LM1. It may reflect their histological feature of the central nervous system. The IIIrd, IVth, and VIth nerves, as well as the IInd, had significantly higher percentages of GQ1b (11.6-13.2%) than the other nerves (5.2-8.4%). The high proportion of GQ1b specific to these three cranial nerves involved in the ocular movement lends support to the role of serum anti-GQ1b antibody in the pathogenetic mechanisms of ophthalmoplegia in Miller Fisher syndrome and Guillain-Barré syndrome.

A controlled study of peripheral neuropathy after bariatric surgery

BACKGROUND

Although peripheral neuropathy (PN) occurs after bariatric surgery (BS), a causal association has not been established.

OBJECTIVES

To ascertain whether PN occurs more frequently following BS vs another abdominal surgery, to characterize the clinical patterns of PN, to identify risk factors for PN, and to assess if nerve biopsy provides pathophysiologic insight.

METHODS

Retrospective review identified patients with PN after BS. The frequency of PN was compared with that of an age- and gender-matched, retrospectively evaluated cohort of obese patients undergoing cholecystectomy.

RESULTS

Of 435 patients who had BS, 71 (16%) developed PN. Patients developed PN more often after BS than after cholecystectomy (4/126; 3%) (p < 0.001). The clinical patterns of PN were polyneuropathy (n = 27), mononeuropathy (n = 39), and radiculoplexus neuropathy (n = 5). Risk factors included rate and absolute amount of weight loss, prolonged gastrointestinal symptoms, not attending a nutritional clinic after BS, reduced serum albumin and transferrin after BS, postoperative surgical complications requiring hospitalization, and having jejunoileal bypass. Most risk factors were associated with the polyneuropathy group. Sural nerve biopsies showed prominent axonal degeneration and perivascular inflammation.

CONCLUSIONS

Peripheral neuropathy (PN) occurs more frequently after bariatric surgery (BS) than after another abdominal surgery. The three clinical patterns of PN after BS are sensory-predominant polyneuropathy, mononeuropathy, and radiculoplexus neuropathy. Malnutrition may be the most important risk factor, and patients should attend nutritional clinics. Inflammation and altered immunity may play a role in the pathogenesis, but further study is needed.

Psychometric evaluation of a new sensory scale in immune-mediated polyneuropathies. Inflammatory Neuropathy Cause and Treatment (INCAT) Group

OBJECTIVE

To perform a psychometric evaluation of the inflammatory neuropathy cause and treatment (INCAT) sensory sumscore (ISS) in sensory-motor immune-mediated polyneuropathies. This new sensory scale was evaluated to strive for uniformity in assessing sensory deficit in these disorders.

METHODS

The ISS comprises vibration and pinprick sense plus a two-point discrimination value and ranges from 0 (normal sensation) to 20 (maximum sensory deficit). Before its clinical use, a panel of expert neurologists concluded that the ISS has face and content validity. The construct validity of the ISS was investigated by correlation and regression studies with additional scales (Nine-Hole Peg Test, 10-Meter Walking Test, a disability sumscore). All scales were applied in 113 patients with a stable neurologic condition (83 patients who experienced Guillain-Barre syndrome [GBS] in the past, 22 with chronic inflammatory demyelinating polyneuropathy [CIDP], 8 patients with a monoclonal gammopathy associated polyneuropathy), and 10 patients with recently diagnosed GBS or CIDP with changing clinical conditions. Reliability of the ISS was evaluated in the stable patients. Its responsiveness was investigated in the patients examined longitudinally.

RESULTS

A moderate to good validity was obtained for the ISS (stable group: r = 0.38 to 0.56, p < or = 0.006; longitudinal group: R = 0.60 to 0.82, p < or = 0.007, except for the association with the 10-Meter Walking Test [p = 0.08]). Acceptable internal consistency, and inter- and intraobserver reliability were demonstrated for the ISS (alpha = 0.68 to 0.87; R = 0.85 to 0.89, p < 0.0001). Standardized response mean scores for the ISS were high (> or =0.8), indicating good responsiveness.

CONCLUSIONS

All psychometric requirements are provided for the the inflammatory neuropathy cause and treatment sensory sumscore. The use of this scale is therefore suggested for bedside evaluation of sensory deficit in the individual patient with a sensory-motor immune-mediated polyneuropathy as well as in clinical trials.

The effects of digital anesthesia on force control using a precision grip

A total of 20 right-handed subjects were asked to perform a grasp-lift-and-hold task using a precision grip. The grasped object was a one-degree-of-freedom manipuladum consisting of a vertically mounted linear motor capable of generating resistive forces to simulate a range of object weights. In the initial study, seven subjects (6 women, 1 man; ages 24-56 yr) were first asked to lift and hold the object stationary for 4 s. The object presented a metal tab with two different surface textures and offered one of four resistive forces (0.5, 1.0, 1.5, and 2.0 N). The lifts were performed both with and without visual feedback. Next, the subjects were asked to perform the same grasping sequence again after ring block anesthesia of the thumb and index finger with mepivacaine. The objective was to determine the degree to which an internal model obtained through prior familiarity might compensate for the loss of cutaneous sensation. In agreement with previous studies, it was found that all subjects applied significantly greater grip force after digital anesthesia, and the coordination between grip and load forces was disrupted. It appears from these data, that the internal model alone is insufficient to completely compensate for the loss of cutaneous sensation. Moreover, the results suggest that the internal model must have either continuous tonic excitation from cutaneous receptors or at least frequent intermittent reiteration to function optimally. A subsequent study performed with 10 additional subjects (9 women, 1 man; ages 24-49 yr) indicated that with unimpaired cutaneous feedback, the grasping and lifting forces were applied together with negligible forces and torques in other directions. In contrast, after digital anesthesia, significant additional linear and torsional forces appeared, particularly in the horizontal and frontal planes. These torques were thought to arise partially from the application of excessive grip force and partially from a misalignment of the two grasping fingers. These torques were further increased by an imbalance in the pressure exerted by the two opposing fingers. Vision of the grasping hand did not significantly correct the finger misalignment after digital anesthesia. Taken together, these results suggest that mechanoreceptors in the fingertips signal the source and direction of pressure applied to the skin. The nervous system uses this information to adjust the fingers and direct the pinch forces optimally for grasping and object manipulation.

A controlled investigation of the cause of chronic idiopathic axonal polyneuropathy

To investigate the aetiology of chronic idiopathic axonal polyneuropathy (CIAP), 50 consecutive patients were compared with 50 control subjects from the same region. There were 22 patients with painful neuropathy and 28 without pain, 26 with sensory neuropathy and 24 with sensory and motor neuropathy. The typical picture was a gradually progressive sensory or sensory and motor neuropathy. It caused mild or sometimes moderate disability, and reduced the quality of life. There was no evidence that alcohol, venous insufficiency, arterial disease or antibodies to peripheral nerve antigens played a significant part. There was a possible history of peripheral neuropathy in the first or second-degree relatives of six patients and no controls (P = 0.01), and claw toes were present in 12 patients and four controls (P = 0.03). Thirty-two per cent of the patients and 14% of the controls had impaired glucose tolerance or fasting hyperglycaemia but, after adjusting for age and sex, the difference was not significant (P = 0.45), even in the painful neuropathy subgroup. The mean (SD) fasting insulin concentrations were significantly (P = 0.01) higher in the patients [75.9 (44.4) mmol/l] than the controls [47.3 (37.9) mmol/l], and the mean was higher still in the painful neuropathy subgroup [92.2 (37.1) mmol/l] (P < 0.0001). However, insulin resistance as assessed using the homeostasis model assessment formula was not significantly greater in the patients, even in those with pain, than the controls. After adjustment for body mass index as well as age and sex, there was no significant difference in the serum cholesterol concentrations, but there were significantly higher triglyceride concentrations in the patients [mean 1.90 (1.41) mmol/l] than the controls [mean 1.25 (0.79] mmol/l) (P = 0.02). In the patients with painful peripheral neuropathy, the mean triglyceride concentration was 2.37 (1.72), which was even more significantly greater compared with the controls (P = 0.003). In conclusion, CIAP is a heterogeneous condition. A logistic regression analysis identified environmental toxin exposure and hypertriglyceridaemia, but not glucose intolerance or alcohol overuse as significant risk factors that deserve further investigation as possible causes of CIAP.