Terminal latency index in polyneuropathy with IgM paraproteinemia and anti-MAG antibody

Conduction slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies: Electrophysiology meets pathology

Nerve conduction studies are usually the first diagnostic step in peripheral nerve disorders and their results are the basis for planning further investigations. However, there are some commonplaces in the interpretation of electrodiagnostic findings in peripheral neuropathies that, although useful in the everyday practice, may be misleading: (1) conduction block and abnormal temporal dispersion are distinctive features of acquired demyelinating disorders; (2) hereditary neuropathies are characterized by uniform slowing of conduction velocity; (3) axonal neuropathies are simply diagnosed by reduced amplitude of motor and sensory nerve action potentials with normal or slightly slow conduction velocity. In this review, we reappraise the occurrence of uniform and non-uniform conduction velocity slowing, conduction block and temporal dispersion in demyelinating, dysmyelinating and axonal neuropathies attempting, with a translational approach, a correlation between electrophysiological and pathological features as derived from sensory nerve biopsy in patients and animal models. Additionally, we provide some hints to navigate in this complex field.

A diagnostic score for anti-myelin-associated-glycoprotein neuropathy or chronic inflammatory demyelinating polyradiculoneuropathy in patients with anti-myelin-associated-glycoprotein antibody

BACKGROUND AND PURPOSE

A diagnostic score was developed to discriminate anti-myelin-associated-glycoprotein (MAG) neuropathy from chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) and applied it to patients with atypical anti-MAG neuropathy.

METHODS

The clinical and electrophysiological features of patients with a diagnosis of typical anti-MAG neuropathy were compared to those of patients with a diagnosis of CIDP. The association of each feature with the diagnosis was assessed in the two groups. Features showing a significant association with the diagnosis were included in a multivariable logistic regression model and adjusted odds ratios were estimated for each feature. A score ranging from 1 to 3 was applied to each feature based on the magnitude of the estimated odds ratios. The score was then applied to patients with a clinical diagnosis of CIDP who also had high anti-MAG antibody titers (CIDP-MAG).

RESULTS

Thirty-one anti-MAG neuropathy patients, 45 typical CIDP patients and 16 CIDP-MAG patients were included. Scores in anti-MAG antibody patients ranged from 1 to 5 and in CIDP patients from -7 to -1. Using the score, 4/16 CIDP-MAG patients were diagnosed to have anti-MAG neuropathy and 12/16 patients to have CIDP. Response to intravenous immunoglobulin in the CIDP-MAG patients classified as CIDP was similar to that of definite CIDP patients and higher than that of anti-MAG neuropathy patients.

CONCLUSIONS

Our score allowed an accurate discrimination to be made, amongst patients with anti-MAG antibodies, of those affected by CIDP and the patients with anti-MAG neuropathy. This score may help proper treatment to be chosen for patients with anti-MAG antibodies with a CIDP-like presentation.

Value of Antibody Determinations in Chronic Dysimmune Neuropathies

Chronic dysimmune neuropathies encompass a group of neuropathies that share immune-mediated pathomechanism. Chronic dysimmune antibody-related neuropathies include anti-MAG neuropathy, multifocal motor neuropathy, and neuropathies related to immune attack against paranodal antigens. Such neuropathies exhibit distinguishing pathomechanism, clinical and response to therapy features with respect to chronic inflammatory demyelinating polyradiculoneuropathy and its variants, which represent the most frequent form of chronic dysimmune neuropathy. This narrative review provides an overview of pathomechanism; clinical, electrophysiological, and biochemical features; and treatment response of the antibody-mediated neuropathies, aiming to establish when and why to look for antibodies in chronic dysimmune neuropathies.

Peripheral neuropathy after viral eradication with direct-acting antivirals in chronic HCV hepatitis: A prospective study

BACKGROUND

HCV-related extra-hepatic complications include peripheral neuropathies, with important prevalence and impact. A recent metanalysis of previous intervention trials concluded for insufficient data to support evidence-based treatments for this complication. In this longitudinal study, we assessed for the first time prevalence and outcome of neuropathy in a cohort of patients with chronic HCV, before and after direct-acting antiviral agent (DAA) treatment.

METHOD

Ninety-four patients (mean age 58.5 ± 9.9, infection duration 22.2 ± 6.3 years) without systemic and metabolic diseases, underwent neurological examination and electroneurography studies before (T0) and 10.4 ± 1.7 months after the end of DAA therapy (T1), and cryoglobulins (CG) assessment. Muscle strength was evaluated by Medical Research Council (MRC) score; neuropathic pain, sensory function, disability, quality of life were assessed by validated questionnaires (DN4, NPSI, SSS, INCAT and Euro-QoL).

RESULTS

At T0, sensory-motor neuropathy was detected in 22 patients (23%), reflexes were depressed in 32 (34%) with no association with infection duration, viral load, age, CG. Neuropathic pain (DN4 ≥4) was present in 37 patients (39%). At T1, out of the 22 patients with altered electroneurography, 3 had died or developed HCC, 4 showed normal electroneurography, and nerve amplitude parameters tended to improve in the whole group. Only 11 patients (12%) had depressed reflexes and 10 (11%) DN4 ≥4 (P < .05 compared to T0). Scores for MRC, questionnaires and Euro-QoL improved significantly (P < .05).

CONCLUSION

Our study confirms the high prevalence of clinical and subclinical peripheral sensory-motor neuropathy in patients with HCV infection and indicates improvement after eradication by DAA. These results support the need for larger intervention studies.

Severe Paraproteinemic Demyelinating Neuropathy With Impaired Excitability of the Distal Segments of the Peripheral Nerves

ABSTRACT

We report clinical and detailed nerve conduction findings in case of polyneuropathy associated with kappa light chains monoclonal gammopathy of undetermined significance with progression to lymphoproliferative disorder. A 55-year-old man had a predominantly distal, chronic (5 years duration), slowly progressive, symmetric, predominantly sensory impairment with sensory ataxia, and mild weakness. M protein was identified by serum protein electrophoresis. The kappa/lambda ratio of free light chains was significantly elevated to 11.96. The cerebrospinal fluid protein level was elevated at 3.5 g/L. This case study has revealed 2 unusual electrophysiological phenomena-a very unusual prolongation of distal motor latencies of compound muscle action potentials (CMAP) up to 86.5 ms and impaired excitability of the distal segments of the peripheral nerves. The distal CMAP areas were considerably lower compared with the proximal CMAP areas. Radiography of the skull revealed osteolytic lesions.

Paraproteinaemic neuropathy: MGUS and beyond

Paraproteinaemic neuropathies comprise a heterogeneous group of neuro-haematological conditions with some distinct neurological, haematological and systemic phenotypes. The spectrum of disease varies from mild to severe, indolent to rapidly progressive and from small fibre sensory involvement to dramatic sensorimotor deficits. The haematological association may be overlooked, resulting in delayed treatment, disability, impaired quality of life and increased mortality. However, the presence of an irrelevant benign paraprotein can sometimes lead to inappropriate treatment. In this review, we outline our practical approach to paraproteinaemic disorders, discuss the utility and limitations of diagnostic tests and the distinctive clinical phenotypes and touch on the complex multidisciplinary management approaches.

Temporal evolution of nerve conduction study abnormalities in anti-myelin-associated glycoprotein neuropathy

BACKGROUND

A distal-predominant demyelinating symmetric pattern is most frequent in patients with neuropathy associated with anti-myelin-associated glycoprotein (MAG) antibodies. The literature however lacks longitudinal data to describe whether this is consistent over time.

METHODS

From the Ottawa Neuromuscular Center database, we identified 23 patients with both immunoglobulin M gammopathy and anti-MAG antibodies. For median, ulnar and fibular motor conduction studies, we analyzed distal latency and amplitude, negative peak duration, terminal latency index (TLI), and conduction velocity. For median, ulnar, sural, and superficial fibular sensory conduction studies, we analyzed distal latency and amplitude. Results were compared for the earliest and the latest data sets.

RESULTS

The mean time interval between the two assessment points was 6.5 years. Median and ulnar motor nerve conduction studies did not show a significant change for any of the parameters tested. There was disproportionate prolongation of median distal motor latency and reduction in TLI, compared to the ulnar nerve. Deep fibular motor conduction studies showed a marked reduction in amplitudes over time. Sensory potentials were recordable in the upper limb in less than 50% at the first study and less than 25% on the most recent study. There was an even larger attrition of recordable sural and superficial fibular sensory potentials.

CONCLUSIONS

Our results highlight the stability of median and ulnar motor conduction study results over a mean observation period of 6.5 years. In contrast, lower limb motor and all sensory potentials show a marked trend toward becoming unrecordable.

Prognostic factor of poor outcome in anti-MAG neuropathy: clinical and electrophysiological analysis of a French Cohort

BACKGROUND

Anti-MAG polyneuropathy (anti-MAG PN) is an immune-mediated peripheral sensorimotor neuropathy characterized by distal demyelination and ataxia. However, this disorder, unlike other immune-mediated neuropathies, is difficult to treat in most cases.

METHOD

We retrospectively collected all anti-MAG PN patients followed in two hospitals for a period of 12 years to determine prognostic factors, especially those that indicated a good response to the various therapeutic strategies used.

RESULTS

Forty-seven patients were included in the study; of these, 61% had a classical 'distal demyelinating pattern', 34.2% had a 'CIDP-like pattern', and the others had an 'axonal pattern'. The most commonly used treatments were intravenous immunoglobulin (IVIg) as the first-line treatment and rituximab as the second- or third-line treatment. No prognostic factor was identified for IVIg, but electrophysiological parameters at onset were better in patients with a good response to rituximab than in non-responder patients, even though mild or high disability was observed in nearly half the patients at last examination.

CONCLUSION

Even though disability seems to progress in most cases despite the treatments used, our results suggest that an early electrophysiological reduction in sensory nerves could be considered a 'red flag' for the prompt initiation of rituximab to try to delay long-term disability.

Outcomes after single-cycle rituximab monotherapy in patients with anti-MAG polyneuropathy: A bi-center experience with an average follow-up of 11 years

Rituximab is efficacious in myelin-associated glycoprotein (MAG) polyneuropathy, but the question on timing of retreatments is open. We studied 21 anti-MAG polyneuropathy patients who responded to a first cycle of rituximab, were followed-up for an average of 11.2 years, and were retreated only when relapsing. Baseline serum B-cell-activating factor (BAFF) levels were measured. Clinical improvements lasted on average 6 years, and as many as 71% of the patients resulted long-lasting responders. Severity of disease and high serum BAFF levels (cut-off ≥860 pg/mL for relapse risk) at onset seemed to predict worse prognosis. Measurements of these variables could help deal with the issue of maintenance rituximab therapy in MAG polyneuropathy.

Value of terminal latency index and sensory electrophysiology in idiopathic and diabetic chronic inflammatory demyelinating polyradiculoneuropathy

OBJECTIVES

To evaluate sensory electrophysiology, terminal latency index (TLI), and treatment response in idiopathic and diabetic chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

METHODS

We performed a retrospective review of 147 patients with CIDP who underwent electrodiagnostic evaluation (January 2000-December 2015). Eighty-nine patients fulfilled electrophysiological criteria described by the Ad hoc Subcommittee of the American Academy of Neurology and Albers et al. Fifty-eight patients were divided into idiopathic (N = 40) and diabetic (N = 18) groups. These groups were compared for age, sex, cerebrospinal fluid protein, response to treatment, sensory response abnormalities, and TLI measurements using chi-square tests for binary and categorical variables and using t-tests and mixed-effects models for continuous variables.

RESULTS

The difference in abnormal rates of sensory responses was significant for the sural nerve, with the idiopathic group having a lower rate than the diabetic group (80% vs. 100%, p < 0.001). No group differences in the TLI measurements were significant.

CONCLUSIONS

Sural sensory responses may have some value in differentiating idiopathic CIDP from diabetic CIDP. Larger prospective studies are needed to confirm our findings.

SIGNIFICANCE

Our study suggests that abnormal sural sensory potentials may have some significance in differentiating idiopathic CIDP from diabetic CIDP.

Long-term disability and prognostic factors in polyneuropathy associated with anti-myelin-associated glycoprotein (MAG) antibodies

AIM OF THE STUDY

Neuropathy associated with IgM monoclonal gammopathy (MGUS) represents distinctive clinical syndrome, characterized by male predominance, late age of onset, slow progression, predominantly sensory symptoms, deep sensory loss, ataxia, minor motor impairment. More than 50% of patients with neuropathy-associated MGUS possess antibodies against myelin-associated glycoprotein (MAG). Purpose of our study was to assess effects on disease progression of demographic, clinical and neurophysiological variables in our large cohort of patients.

MATERIALS AND METHODS

Forty-three Caucasians patients were followed every eight months for median duration time of 93 months. Extremity strength was assessed with Medical Research Council (MRC) Scale, disability with overall disability status scale (ODSS), modified Rankin Scale and sensory function with Inflammatory Neuropathy Cause and Treatment (INCAT) sensory scale (ISS). Statistical analyses were conducted with parametric or non-parametric measures as appropriate. Survival analysis was used to test predictive value of clinical, demographical and neurophysiological variables. Variance analysis was conducted to explain difference on MRC between patients and groups at different time from onset.

RESULTS

Results showed that demyelinating pattern, older age and absence of treatment were significant risk factors for disability worsening. No other factors emerged as predictors including gender, ataxia and tremor at baseline, level of anti-MAG and IgM protein concentration in serum. Despite worsening of all outcome measures between first and last visit, quality of life (HRQol) judged by patients did not vary significantly.

CONCLUSIONS

Our study provides evidence that electrophysiologic pattern, age of onset and absence of treatment are strong predictor of prognosis in anti-MAG polyneuropathy.

Heterogeneity of Polyneuropathy Associated with Anti-MAG Antibodies

Polyneuropathy associated with IgM monoclonal gammopathy and anti-myelin associated glycoprotein (MAG) antibodies is an immune-mediated demyelinating neuropathy. The pathophysiology of this condition is likely to involve anti-MAG antibody deposition on myelin sheaths of the peripheral nerves and it is supposed to be distinct from chronic inflammatory demyelinating neuropathy (CIDP), another immune-mediated demyelinating peripheral neuropathy. In this series, we have retrospectively reviewed clinical and laboratory findings from 60 patients with polyneuropathy, IgM gammopathy, and anti-MAG antibodies. We found that the clinical picture in these patients is highly variable suggesting a direct link between the monoclonal gammopathy and the neuropathy. Conversely, one-third of patients had a CIDP-like phenotype on electrodiagnostic testing and this was correlated with a low titer of anti-MAG antibodies and the absence of widening of myelin lamellae. Our data suggest that polyneuropathy associated with anti-MAG antibodies is less homogeneous than previously said and that the pathophysiology of the condition is likely to be heterogeneous as well with the self-antigen being MAG in most of the patients but possibly being another component of myelin in the others.

The usefulness of terminal latency index of median nerve and f-wave difference between median and ulnar nerves in assessing the severity of carpal tunnel syndrome

The calculated electrophysiological parameters, such as terminal latency index (TLI), residual latency, modified F ratio, and F-wave inversion, have been investigated as a diagnostic tool for detection of early stage of carpal tunnel syndrome (CTS) in the literature. However, the correlation of these calculated electrophysiological parameters with the clinical severity of CTS has not been reported. The aim of this study was to determine the correlation of the calculated electrophysiological parameters and clinical severity in patients with CTS. A retrospective study was performed with 212 hands of 106 CTS patients. The CTS hands were classified as asymptomatic, mild, moderate, and severe according to the clinical severity. The distal motor latency and distal motor conduction velocity of median nerve, minimal F-wave latency of median and ulnar nerves, and sensory nerve conduction velocity in the finger-wrist and palm-wrist segment of median nerve (SNCV f-w and SNCV p-w) were obtained in a conventional nerve conduction study. The TLI, residual latency, and modified F ratio of the median nerve and the difference of minimal F-wave latencies between the median and ulnar nerves (F-diff M-U) were calculated. The distal motor latency, residual latency, and F-diff M-U were significantly increased according to the clinical severity of CTS. The motor conduction velocity, SNCV p-w, SNCV f-w, TLI, and modified F ratio were significantly decreased according to the clinical severity of CTS. In analyses of variance and Kruskal-Wallis test, we used the Scheffe test as a post-hoc comparison analysis. The TLI, F-diff M-U, and SNCV f-w showed a significant difference among all groups of each CTS severity. The sensitivity, specificity, and cut-off value of TLI, F-diff M-U, and SNCV f-w between asymptomatic and mild, mild and moderate, and moderate and severe CTS groups were calculated by using receiver operating characteristic curve analysis. The cut-off values of TLI, F-diff M-U, and SNCV f-w between the asymptomatic and mild CTS groups were, respectively, 0.33 millisecond, 0.3 millisecond, and 40 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between mild and moderate were, respectively, 0.27 millisecond, 2.3 milliseconds, and 34.8 cm/second. The cut-off values of TLI, F-diff M-U, and SNCV f-w between moderate and severe CTS groups were, respectively, 0.20 millisecond, 4.2 milliseconds, and 26.4 cm/second. We found that calculated electrophysiological parameters of conventional nerve conduction study could be a good indicator to determine the severity of CTS.

Ulnar entrapment neuropathy in patients with type 2 diabetes mellitus: an electrodiagnostic study

AIMS

This study aimed to assess the prevalence and electrophysiological features of ulnar entrapment neuropathy in patients with type 2 diabetes mellitus (DM).

METHODS

Nerve conduction studies (NCS) were performed in a sample of consecutive diabetic patients aged 25-75 years, referred by the Diabetology Unit. NCS of the median, ulnar, radial, peroneal and sural nerves were performed on the non-dominant side. Median entrapment neuropathy at the wrist (MNW) and ulnar neuropathy at the elbow (UNE) and wrist (UNW) were diagnosed according to standard electrodiagnostic criteria.

RESULTS

Sixty-four patients were enrolled, 28 male (44%), average age 61, average DM duration 14.5 years. Polyneuropathy was diagnosed in 45 subjects (70%). UNE was detected in 22 patients (34%) (4 did not have polyneuropathy), in the abductor digiti minimi in 16, the first interosseus in 14 and in both in 8. UNW was detected in 7 (11%) subjects and MNW in 40 (63%). NCS alterations consistent with ulnar neuropathy were detected in a high proportion of patients (45%), suggesting that the ulnar nerve is very susceptible to focal entrapment in DM.

CONCLUSIONS

Upper limb sensory and motor NCS, including motor conduction velocity across the elbow, should be considered in the staging of DM patients.

Ulnar sensory-motor amplitude ratio: a new tool to differentiate ganglionopathy from polyneuropathy

The objective of this study was to evaluate if the ratio of ulnar sensory nerve action potential (SNAP) over compound muscle action potential (CMAP) amplitudes (USMAR) would help in the distinction between ganglionopathy (GNP) and polyneuropathy (PNP).MethodsWe reviewed the nerve conductions studies and electromyography (EMG) of 18 GNP patients, 33 diabetic PNP patients and 56 controls. GNP was defined by simultaneous nerve conduction studies (NCS) and magnetic resonance imaging (MRI) abnormalities. PNP was defined by usual clinical and NCS criteria. We used ANOVA with post-hoc Tukey test and ROC curve analysis to compare ulnar SNAP and CMAP, as well as USMAR in the groups.ResultsUlnar CMAP amplitudes were similar between GNP x PNP x Controls (p=0.253), but ulnar SNAP amplitudes (1.6±3.2 x 11.9±9.1 × 45.7±24.7) and USMAR values (0.3±0.3 × 1.5±0.9 × 4.6±2.2) were significantly different. A USMAR threshold of 0.71 was able to differentiate GNP and PNP (94.4% sensitivity and 90.9% specificity).ConclusionsUSMAR is a practical and reliable tool for the differentiation between GNP and PNP.

Antibody testing in peripheral nerve disorders

The identification of autoantibodies associated with dysimmune neuropathies was a major contribution to the characterization of peripheral nerve disorders, the understanding of their pathophysiology, and the clinical diagnosis of neuropathies. Antibodies directed to GM1, GQ1b, and disyalilated gangliosides, and anti-MAG antibodies are very useful in the diagnosis of acute or chronic motor or sensory-motor neuropathies with or without monoclonal IgM. Anti-onconeural anti-Hu and anti-CV2/CRMP antibodies allow when they are detected the diagnosis of paraneoplastic neuropathies. This chapter focuses on the description of these antibodies as diagnostic markers and on their immunopathogenesis. We give a background overview on the origin of these antibodies, their detection, and review those studies, which clearly show that these antibodies are capable of binding to the target tissues in peripheral nerve and thereby can exert a variety of pathophysiological effects. The corresponding electrophysiological and histological changes observed both in human and animal models are exemplified in order to get a better understanding of the immune mechanisms of these antibody-mediated neuropathies.

POEMS syndrome presenting with acute demyelinating polyneuropathy: increased terminal latency indices and uniform demyelination

We herein report a case of polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes (POEMS) syndrome presenting with acute Guillain-Barré syndrome (GBS)-like features. The patient was healthy, except for mild dilated cardiomyopathy. She was unable to walk within ten days of the onset of weakness. A nerve conduction study (NCS) showed length-dependent, symmetric and non-focal demyelinating features with increased terminal latency indices (TLIs) in the lower limbs. Following the administration of intravenous immunoglobulin infusion, the proximal weakness of the lower extremities improved; however, the pleural effusion was aggravated and ascites newly developed. On further work-ups, splenomegaly, M-protein and sclerotic bone changes were observed. This case suggests that, although rare, POEMS syndrome can present with acute demyelinating polyneuropathy resembling GBS and that characteristic NCS features such as increased TLI and uniform demyelination are helpful for the early diagnosis of POEMS syndrome.

Neurophysiological approach to disorders of peripheral nerve

Disorders of the peripheral nerve system (PNS) are heterogeneous and may involve motor fibers, sensory fibers, small myelinated and unmyelinated fibers and autonomic nerve fibers, with variable anatomical distribution (single nerves, several different nerves, symmetrical affection of all nerves, plexus, or root lesions). Furthermore pathological processes may result in either demyelination, axonal degeneration or both. In order to reach an exact diagnosis of any neuropathy electrophysiological studies are crucial to obtain information about these variables. Conventional electrophysiological methods including nerve conduction studies and electromyography used in the study of patients suspected of having a neuropathy and the significance of the findings are discussed in detail and more novel and experimental methods are mentioned. Diagnostic considerations are based on a flow chart classifying neuropathies into eight categories based on mode of onset, distribution, and electrophysiological findings, and the electrophysiological characteristics in each type of neuropathy are discussed.

Pupil-involving third nerve palsy as a manifestation of anti-myelin-associated glycoprotein neuropathy

A 56-year-old man developed a pupil-involving left third nerve palsy. Imaging studies of the brain and intracranial vessels were normal. Neurological examination demonstrated a sensory polyneuropathy and mild distal weakness. Nerve conduction studies showed prolonged distal motor latencies. An enzyme-linked immunosorbent assay test detected high titers of anti-myelin-associated glycoprotein (MAG) antibodies. The patient improved with prednisone and rituximab treatment. Anti-MAG neuropathy should be considered when evaluating a patient with an undiagnosed cranial neuropathy, especially in the setting of a sensory neuropathy.

Polyneuropathy associated with IgM vs IgG monoclonal gammopathy: comparison between clinical and electrophysiological findings

OBJECTIVE

The neuropathy associated with IgM monoclonal gammopathy (IgM-MG) is regarded as a sensorimotor, mainly demyelinating neuropathy. It is not fully known whether the neuropathy in IgG-MG is caused by the same mechanisms and shows the same electrophysiological characteristics. We aimed at making a comparison between clinical and neurophysiological findings in these two conditions.

PATIENTS AND METHODS

Twenty-seven patients with IgM-associated neuropathy [18 with anti-myelin-associated glycoprotein (anti-MAG) antibodies] were compared with 15 age-matched patients with IgG-associated neuropathy.

RESULTS

Patients with IgM-associated neuropathy (especially those with anti-MAG antibodies) had significantly clinically more severe disabilities with involvement of both motor and sensory functions compared with patients with IgG-associated neuropathy in whom clinical sensory disturbances were more prominent than motor dysfunction. Motor and sensory conduction velocities were significantly lower and distal latencies significantly longer in the IgM group than in the IgG group concerning the median, ulnar and peroneal nerves. Fifty-four per cent of the patients in the IgM group did not present a sensory response of the median nerve vs 13% in the IgG group. There was also a significant difference concerning absent responses from the peroneal and sural nerves in the IgM vs IgG group (peroneal: 48% vs 13%, sural: 88% vs 27%).

CONCLUSION

Polyneuropathy associated with IgM-MG, especially when associated with anti-MAG antibodies, appears to have more of a demyelinating involvement that meets the criteria for demyelination. This was not as clear in those associated with IgG. The IgG neuropathy showed less and milder deficit in the electrophysiological studies.

Entrapment in anti myelin-associated glycoprotein neuropathy

Anti-myelin associated glycoprotein (MAG) neuropathy is a chronic disorder in which IgM antibodies react with Schwann cell glycoproteins, including MAG and peripheral myelin protein 22 (PMP22). Nerve conduction studies show features of axon loss and predominantly distal slowing consistent with demyelination. Because a genetic loss of PMP22 function yields hereditary neuropathy with liability to pressure palsies (HNPP), loss of PMP22 function due to anti- MAG antibodies may result in increased sensitivity to entrapment. We investigated this by performing standardized electrophysiological studies in 16 patients with anti-MAG neuropathy and 16 disease controls with genetically confirmed HNPP. Disproportionate slowing relative to adjacent segments occurred in similar proportions of patients with anti-MAG neuropathy and HNPP, and was of the same magnitude in each group. Affected were the elbow, carpal tunnel and the wrist-hand segments of the median and ulnar nerves. However, in anti-MAG neuropathy as compared to HNPP, absolute values of distal motor latencies and conduction velocities outside entrapment sites were slower and amplitudes were lower. In conclusion, increased sensitivity for entrapment may occur in anti-MAG neuropathy and contribute to part of the nerve damage.

Subclinical diabetic neuropathy with normal conventional electrophysiological study

BACKGROUND

For early detection and prevention of diabetic neuropathy, it is important to identify subclinical diabetic neuropathy. Routine nerve conduction study often fails to detect early stage of neuropathy.

OBJECTIVES

The purpose of this study is to evaluate the clinical usefulness of electrophysiological indexes in detecting early diabetic neuropathy with no objective clinical or electrophysiological abnormalities.

MATERIALS AND METHODS

Nerve conduction study of upper/lower limbs was investigated in 31 subclinical diabetic neuropathy patients with normal nerve conduction studies(group I), 38 clinical diabetic neuropathy patients with normal nerve conduction studies(group II) and 31 normal controls. Residual latency (RL), terminal latency index (TLI) and modified F ratio (MFR) were calculated and compared among groups.

RESULTS

Compared with controls, MFR of lower limbs and TLI of both upper/lower limbs were significantly decreased in both group I and II (p<0.05). RL was increased in both groups, but the difference was not statistically significant. Comparing the indexes between group I and II, there was no significant difference.

CONCLUSIONS

RL, TLI and MFR, which reflect distal conduction slowing, may be useful indexes to identify subclinical diabetic neuropathy. The results also suggest that electrophysiological changes that are obscured in routine nerve conduction study are present before the clinical manifestation.

Terminal latency index in neuropathy with antibodies against myelin-associated glycoproteins

Neuropathy with antibodies against myelin-associated glycoproteins (MAG/SGPG-N) and hereditary sensorimotor neuropathy type 1 (HMSN1) are characterized by chronic demyelination with little conduction block. Electrodiagnostic studies suggest that in HMSN1 conduction slowing occurs uniformly along the nerve, whereas in MAG/SGPG-N it is predominantly distal. Some but not all previous reports have shown that the terminal latency index (TLI) was useful to distinguish MAG/SGPG-N from chronic idiopathic demyelinating polyneuropathy. We compared median TLI from 21 patients with MAG/SGPG-N with those obtained from 26 patients with HMSN1, 20 with HMSN2, and 12 healthy volunteers. All patients with TLI <0.26 had MAG/SGPG-N, and all patients with TLI > or =0.32 had HMSN1. In the remaining patients with intermediate TLI values, ulnar distal motor latency (DML) aided in differentiation between MAG/SGPG-N and HMSN1 with an overall sensitivity of 100% and specificity of 98%. In conclusion, median TLI in combination with ulnar DML can further guide the demyelinating neuropathy evaluation toward hereditary or autoimmune causes.

[Polyneuropathy involving cranial nerves associated with monoclonal IgM antibodies with anti-MAG/SGPG/SGPLG/sulfatides activity]

INTRODUCTION

A typically distal and symmetrical, slowly progressive sensorimotor demyelinating neuropathy is caused by monoclonal IgM against myelin-associated glycoprotein (MAG) and SGPG, SGLPG glycolipids in the context of a benign IgM paraproteinemia. We studied a patient with a neuropathy that fulfilled the diagnostic criteria for CIDP in whom IgM kappa anti-MAG/SGPG/SGLPG were detected.

OBSERVATION

The patient was a 57-year-old man who had developed a slowly progressive distal sensorimotor neuropathy, involving the lower then upper limbs, with cranial nerves palsies (oro-pharyngo-laryngo territory). ENMG showed a demyelinating neuropathy with a disproportionate slowing of conduction in distal segments of motor and axonal features in the lower limbs. The first routine laboratory analysis revealed negative or normal findings. Several serum protein electrophoreses were normal. The third cerebrospinal fluid examination demonstrated a moderate and late rise in CSF protein level with no cells. Monoclonal IgM-kappa against MAG/SGPG/SGLPG, was detected; anti-MAG antibody titre in the serum was 20 059 BTU (N<1000). A small IgM-kappa paraprotein was identified by immunofixation. Electron microscopy failed to show nerve fibers with widening of outer lamellae of the myelin. There is no clinical improvement after different treatments, immunoglobulins IV, cortisteroids, plasma exchange, rituximab.

CONCLUSION

It is not known whether this neuropathy is an atypical form of PNMAG or an CIDP associated with anti-MAG. When ENMG show a disproportionate slowing of conduction in distal segments of motor nerves, one should screen the serum with immunofixation to identify small monoclonal components. If IgM-MGUS is present, search should be undertaken for anti-MAG/SGPG/SGLPG antibodies. Diagnosis enables optimal treatment using, in severe cases, expensive current strategies with immunoglobulins IV, plasma exchange, and corticosteroids, or, in the event of no response, rituximab before resorting to more toxic drugs like cyclophosphamide.

Electrophysiological findings of peripheral neuropathy in newly diagnosed type II diabetes mellitus

This study was aimed at assessing the electrophysiological signs of peripheral neuropathy in diabetes mellitus (DM) type II patients at diagnosis. Nerve conduction studies (NCS) of median, ulnar, peroneal, tibial and sural nerves were performed in 39 newly diagnosed DM subjects and compared to those of 40 healthy controls. Metabolic indices were also investigated. Electrophysiological alterations were found in 32 (82%) of the DM patients, and more than half of them (62.2%) showed multiple (two to five) abnormal parameters. Because most of the subjects (84.4%) had from two to five nerves involved, these alterations were widespread in the seven nerves evaluated. Forty-two percent of the patients had NCS alterations suggestive of distal median mononeuropathy, implying that metabolic factors in DM make the median nerve more susceptible to focal entrapment. A reduced sensory nerve action potential (SNAP) amplitude was observed in the median nerve in 70% of the patients, in the ulnar in 69% and in the sural nerve only in 22%. In the presence of a decrease in the SNAP amplitude of the ulnar or median nerve, the SNAP amplitude of the sural nerve was normal in 82 or 80% of the subjects, respectively. This finding may be in keeping with a distal involvement of the sensory fibres, as explored by routine median or ulnar NCS. No correlation was found between metabolic indices and NCS parameters. In conclusion, a high percentage of newly diagnosed DM patients show signs of neuropathy, and upper limb nerve sensory NCS seem to be more sensitive in detecting it than lower limb NCS.

Length dependence in polyneuropathy associated with IgM gammopathy

OBJECTIVE

In polyneuropathy associated with monoclonal IgM gammopathy, nerve conduction studies may show disproportionate distal slowing consistent with segmental demyelination. This was suggested to represent a length-dependent demyelinating process, starting in distal and proceeding to proximal segments. Because the evidence for this is incomplete, we assessed whether length dependence occurs in IgM neuropathy.

METHODS

In 22 patients with IgM neuropathy, 20 disease controls with chronic inflammatory demyelinating polyneuropathy (CIDP) and 36 normal controls, we investigated motor conduction, sensory conduction, and needle electromyography for nerves with short, intermediate-length, and long axons as well as conduction in short segments of the ulnar nerve from proximal to distal. To compare variables in nerves of different length, we normalized individual values with respect to the median in normal controls.

RESULTS

In IgM neuropathy, distal slowing and features of axon loss increased with nerve length, and ulnar nerve conduction became gradually slower from proximal to distal when the elbow segment was excluded. In CIDP, no clear length dependence was found except for distal amplitude.

INTERPRETATION

The disproportionate distal slowing in IgM neuropathy may be part of a length-dependent process, assuming that this process is randomly distributed due to a generalized exposure to IgM.

Immunodetection of anti-MAG IgM antibody by cross-reactivity to LA-N-1 neuroblastoma cells

Demyelinating polyneuropathiy associated with IgM paraproteinemia and high titers of anti-MAG IgM antibodies (MAG-PN) is considered different from chronic inflammatory demyelinating polyneuropathy, particularly because of the poorer response to treatment of MAG-PN patients. Therefore, anti-MAG anitbodies may have relevant prognostic value. Available anti-MAG antibody assays require central nervous system myelin proteins from autopsied human brains. This study investigated the feasibility of detecting anti-MAG antibody by immunofluorescence and flow cytometry using a panel of human neuroblastoma cell lines as targets. We report here on the evaluation of the LA-N-1 cell line as an appropriate substrate for the detection of anti-MAG antibody by indirect immunoflourescence.

Different clinical, electrophysiological and immunological features of CIDP associated with paraproteinaemia

Chronic inflammatory demyelinating polyneuropathy (CIDP) is frequently associated with monoclonal gammopathies of undetermined significance (MGUS), Waldenström disease and osteosclerotic myeloma. There are still controversies about the role of these paraproteinaemias in determining the clinical features and the response to treatment of CIDP. We review the clinical, electrophysiological and immunological features and the response to treatment of patients with CIDP associated with paraproteinaemias. The available literature suggest some conclusions: presence of antimyelin-associated glycoprotein (MAG) antibody (Ab) identifies patients with mainly sensory CIDP and low response to treatment; CIDP associated with IgM-paraproteinaemia without anti-MAG Ab probably are similar to CIDP not associated with paraproteinaemia as well as CIDP with IgG- or IgA-MGUS; however, some patients with IgA-MGUS can show features similar to CIDP with IgM paraproteinaemia and anti-MAG Ab. Low response to immunomodulating treatment in patients with mainly motor CIDP should prompt a careful research of an underlying osteosclerotic myeloma.

Severe chronic sensory-motor polyneuropathy: coexistence of 3 unrelated etiologies in a type 1 diabetic patient. A case report and review of the literature

We present the case of a 58-year-old man, who has suffered from type 1 diabetes mellitus since he was young. He had monoclonal IgM kappa gammopathy of undetermined significance and high anti-MAG antibody titer. He developed a polyneuropathic picture with the clinical and laboratory features of chronic inflammatory demyelinating polyneuropathy within the span of approximately 2 years. He benefited from IV administration of high doses of immunoglobulins. Investigation of all parameters, but particularly of the clinical phenotype, can lead to a better definition of the polyneuropathic picture, especially for therapeutic and prognostic purposes.

Nerve conduction studies in selected peripheral nerve disorders

PURPOSE OF REVIEW

The physiological properties of nerve and muscle are influenced by pathological changes and the aim of this review is to discuss recent contributions of electrophysiological studies to the understanding and diagnosis of selected peripheral nerve disorders. The relationships between pathology and physiology emphasize the close interdependence between electrophysiological studies, clinical deficits and other laboratory information. Attention should be paid to the strengths and limitations of electrophysiological methods, considering their impact on diagnosis and treatment of patients.

RECENT FINDINGS

Several studies have shown particular pathophysiological profiles associated with different antibody subtypes in autoimmune peripheral neuropathies and this association further supports the suggestion of pathological specificity in both acute and chronic neuropathy. The sensitivity and specificity of physiological profiles therefore become increasingly important since some of these neuropathies are accessible to treatment. On the other hand, the pathophysiological and clinical profiles may be heterogeneous in patients with some disorders. This could be related to a more indistinct division between different types of pathology with increased understanding of pathogenetic mechanisms. Moreover, new insights into disturbed axonal function have stimulated attempts to develop methods to explore normal and diseased human nerve function.

SUMMARY

The exploration of axonal membrane and ion-channel function has become accessible using studies of excitability and are of potential value where conventional studies only provide nonspecific evidence of the number of fibers and the integrity of myelin. These studies will presumably become increasingly important in the years ahead considering the lack of understanding of the functional disturbances in axonal neuropathies.

Chronic inflammatory demyelinating polyradiculoneuropathy

In chronic inflammatory demyelinating polyradiculopathy differing clinical subtypes are beginning to emerge as has already occurred with the Guillain-Barré syndrome. However, neither pathogenic correlates nor particular therapeutic approaches have yet been defined for these subgroups. The neurophysiological techniques of terminal latency index and of modified F ratio help differentiate chronic inflammatory demyelinating polyradiculopathy from IgM paraproteinaemic neuropathy. Diagnosis may be assisted by magnetic resonance imaging studies in which enlarged nerve roots and plexuses and gadolinium enhancement may be evident. Further insight into pathogenesis has come from studies showing pathogenic antibodies in a small percentage of patients. Immunohistological studies examining the presence of adhesion, co-stimulatory and antigen presenting molecules in nerve biopsies have shown that T cell activation can be initiated and perpetuated within nerve and that Schwann cells possess the necessary markers to function as antigen presenting cells. Recent clinical trials have confirmed the therapeutic short term efficacy of intravenous immunoglobulin and Prednisone.