Complement-mediated demyelination in patients with IgM monoclonal gammopathy and polyneuropathy

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.

Immunotherapy for IgM anti-Myelin-Associated Glycoprotein paraprotein-associated peripheral neuropathies

BACKGROUND

Serum monoclonal anti-Myelin Associated Glycoprotein antibodies may be pathogenic in some patients with IgM paraprotein and demyelinating neuropathy. Immunotherapies aimed at reducing the level of these antibodies might be expected to be of benefit in the treatment of the neuropathy. Many potential therapies have been described in small trials, uncontrolled studies and case reports.

OBJECTIVES

To examine the efficacy of any form of immunotherapy in reducing disability and impairment resulting from IgM anti-Myelin Associated Glycoprotein paraprotein-associated demyelinating peripheral neuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group register (August 2002) and MEDLINE (January 1966 - August 2002) and EMBASE (January 1980 - August 2002) for controlled trials, checked the bibliographies to identify other controlled trials and contacted authors and other experts in the field.

SELECTION CRITERIA

Types of studies: randomised or quasi-randomised controlled trials.

TYPES OF PARTICIPANTS

patients of any age with anti-Myelin Associated Glycoprotein antibody associated demyelinating peripheral neuropathy with monoclonal gammopathy of undetermined significance of any severity. Types of interventions: any type of immunotherapy. Types of outcome measures: Primary: improvement in the Neuropathy Disability Score or Modified Rankin Scale six months after randomisation Secondary: Neuropathy Disability Score and/or the Modified Rankin Score 12 months after randomisation. Ten metre walk time, subjective clinical scores and electrophysiological parameters at six and 12 months after randomisation. IgM paraprotein levels and anti-Myelin Associated Glycoprotein antibody titres six months after randomisation. Adverse effects of treatments.

DATA COLLECTION AND ANALYSIS

We identified six randomised controlled trials of which five were included after discussion between the authors. One author extracted the data and the other checked them. No missing data could be obtained from authors.

MAIN RESULTS

The five eligible trials used four of the many available immunotherapy treatments. Only two had comparable interventions and outcomes but these were only short-term studies. There were no significant benefits of the treatments used in the predefined outcomes. However intravenous immunoglobulin showed benefits in terms of improved Modified Rankin Scale at two weeks and 10 metre walk time at four weeks. Serious adverse effects of intravenous immunoglobulin are known to occur from observational studies but none were encountered in these trials.

REVIEWER'S CONCLUSIONS

There is inadequate reliable evidence from trials of immunotherapies in anti-Myelin Associated Glycoprotein paraproteinaemic neuropathy to recommend any particular immunotherapy treatment. Intravenous immunoglobulin is relatively safe and may produce some short-term benefit. Large well designed randomised trials are required to assess the efficacy of promising new therapies.

IFN-alpha as induction and maintenance treatment of patients newly diagnosed with Waldenström's macroglobulinemia

Waldenström's macroglobulinemia is a rare malignant disorder of B lymphocytes. There are no studies on the use of interferon-alpha (IFN-alpha) as frontline therapy in this disease. Between April 1991 and September 2000, we treated 21 newly diagnosed patients using 8 mg/m(2) chlorambucil and 40 mg/m(2) prednisone p.o. daily for 10 days and 3 megaU/m(2) IFN-alpha three times a week. Patients who responded after induction continued receiving IFN until relapse or death. We found a high frequency of peripheral neuropathy (43%) and grade 3 diffuse marrow fibrosis (43%). Objective response was achieved in 12 (57%) patients, including 4 (19%) complete responders. Median time from treatment to response was 8 months (range 3-18). Median progression-free survival was 70 months (95% CI 47-93), and overall survival was 91 months (95% CI 50-132). Patients who achieved objective response lived longer (91 vs. 33 months, p < 0.03), as did patients who had lactic dehydrogenase (LDH) < 180 U/L (89 vs. 54 months, p < 0.01). Grade 3 hematologic toxicity was observed during induction in 5 patients. IFN-alpha is an effective agent for the induction and maintenance treatment of Waldenström's macroglobulinemia patients. LDH > 180 U/L and failure to respond are adverse prognostic factors.

The role of macrophages in immune-mediated damage to the peripheral nervous system

Macrophage-mediated segmental demyelination is the pathological hallmark of autoimmune demyelinating polyneuropathies, including the demyelinating form of Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy. Macrophages serve a multitude of functions throughout the entire pathogenetic process of autoimmune neuropathy. Resident endoneurial macrophages are likely to act as local antigen-presenting cells by their capability to express major histocompatibility complex antigens and costimulatory B7-molecules, and may thus be critical in triggering the autoimmune process. Hematogenous infiltrating macrophages then find their way into the peripheral nerve together with T-cells by the concerted action of adhesion molecules, matrix metalloproteases and chemotactic signals. Within the nerve, macrophages regulate inflammation by secreting several pro-inflammatory cytokines including IL-1, IL-6, IL-12 and TNF-alpha. Autoantibodies are likely to guide macrophages towards their myelin or primarily axonal targets, which then attack in a complement-dependent and receptor-mediated manner. In addition, non-specific tissue damage occurs through the secretion of toxic mediators and cytokines. Later, macrophages contribute to the termination of inflammation by promoting T-cell apoptosis and expressing anti-inflammatory cytokines including TGF-beta1 and IL-10. During recovery, they are tightly involved in allowing Schwann cell proliferation, remyelination and axonal regeneration to proceed. Macrophages, thus, play dual roles in autoimmune neuropathy, being detrimental in attacking nervous tissue but also salutary, when aiding in the termination of the inflammatory process and the promotion of recovery.

Anti-GM(2) IgM antibody-induced complement-mediated cytotoxicity in patients with dysimmune neuropathies

Anti-GM2 IgM antibodies have been reported in some patients with dysimmune neuropathy or lower motor neuron syndrome. To determine whether these antibodies can induce complement-dependent cytolysis we performed a cytotoxicity assay on neuroblastoma cells with sera from seven patients with demyelinating dysimmune neuropathies and high titers of anti-GM2 IgM. As controls we used sera from seven patients with other anti-neural reactivities, six with the same neuropathies but no anti-GM2 or other anti-neural reactivity and from eight normal subjects. Of the seven positive sera tested, six induced complement-mediated cytotoxicity, while none of the controls had any relevant effect on neuroblastoma cells. Preincubation of positive sera with purified GM2 removed cytotoxic activity. Affinity purified anti-GM2 IgM had the same cytotoxic anti-GM2 effect of whole serum while serum or complement alone did not have any effect. In four anti-GM2-positive patients the percentage of cell lysis correlated with anti-GM2 titers and with IgM staining of neuroblastoma cells while in two the cytotoxic effect was higher than expected from antibody titers. Complement-mediated cell lysis induced by anti-GM2 IgM antibodies may be a possible mechanism of neural damage in patients with dysimmune neuropathy and high titers of anti-GM2 IgM antibodies.

Treatment experience in patients with anti-myelin-associated glycoprotein neuropathy

We report our experience with 24 consecutively treated patients (15 men and 9 women, median age 64 years) with anti-myelin-associated glycoprotein (anti-MAG) neuropathy. The rates of response to plasma exchange (40%), immune globulin (16%), and cyclophosphamide-based therapy (36%) were similar. Five (24%) responded to the first treatment modality, 32% to a second, alternative modality, and 31% to a third. Only 4 of 12 responders had sustained improvement; the others relapsed after a median of 7 months. In those 4 patients, the median immunoglobulin M (IgM) level dropped by 25% compared to an increase of 24% in the nonresponders (P = 0.04). Thus, most patients with anti-MAG neuropathy failed to have sustained improvement after treatment, and none of the therapies emerged as superior. Disability improved transiently after therapy in approximately 50% of cases. A 25% reduction of the IgM level predicted sustained improvement, but was difficult to achieve. There were no clinical or electrodiagnostic features associated with a treatment response, nor did a reduction of the anti-MAG antibody titer correlate with clinical improvement.

Anti-sulfatide IgM antibodies in peripheral neuropathy

Anti-sulfatide IgM antibodies have been recently associated with neuropathy but the clinical and electrophysiological correlations of this reactivity remains unclear. We reviewed the clinical and electrophysiological features of patients with high anti-sulfatide titers detected in our laboratory from 1991 to 1998. Of the 564 patients with different neurological diagnosis tested by enzyme-linked immunosorbent assay (ELISA), 11 had high anti-sulfatide IgM titers (>1/8000), 26 had titers of 1/8000 while 78 had titers of 1/4000. All patients with high anti-sulfatide IgM titers had a chronic, dysimmune, mostly sensorimotor neuropathy that in seven was associated with IgM monoclonal gammopathy. In most of these patients electrophysiological and morphological studies were consistent with a predominantly demyelinating neuropathy frequently associated with prominent axonal loss. Antibody titers of 1/8000, though always associated with neuropathy, did not correlate with a particular form or cause of neuropathy, while lower titers were equally distributed in patients with different neurological disorders. Our study indicate that high anti-sulfatide IgM titers (>1/8000) are highly predictive for a chronic, dysimmune, mostly demyelinating neuropathy often associated with IgM monoclonal gammopathy, and may therefore have potential diagnostic relevance.

The polyneuropathy associated with Waldenström's macroglobulinaemia can be treated effectively with chemotherapy and the anti-CD20 monoclonal antibody rituximab

A 50-year-old male developed headache, impaired balance, visual defects and severe deafness. Ten months later he presented with markedly reduced power and tremor of his right arm. Waldenström's macroglobulinaemia (WM) with accompanying polyneuropathy was diagnosed. The patient received chemotherapy, which resulted in a partial improvement of the arm tremor. Subsequently, he was treated with rituximab (4 x 375 mg/m2), leading to complete resolution of the tremor and the paresis of his arm. Additionally, his headache and imbalance disappeared. Fifteen months after rituximab therapy he remained free of any neurological symptoms. This is the first report showing that WM-associated polyneuropathy can be treated effectively with a combination of chemotherapy and the anti-CD20 monoclonal antibody rituximab.

Long-term clinical and neurophysiological follow-up of patients with peripheral, neuropathy associated with benign monoclonal gammopathy

The incidence of hematological malignancy in patients with monoclonal gammopathy of undetermined significance (MGUS) has been assessed as 17% to 25%. To ascertain whether this is true of neuropathy associated with MGUS, a long-term (5-42 years) retrospective clinical and neurophysiological follow-up was conducted in 50 cases (immunoglobulin M [IgM], n = 38; IgG, n = 11; IgA, n = 1). Only three patients developed hematological malignancy. Of 25 survivors with IgM paraproteinemia, 7 had myelin-associated glycoprotein antibodies with typical clinical features. Evoked distal muscle amplitudes were significantly smaller than for the other paraprotein classes. Preferential distal demyelination manifested by relative prolongation of distal motor latency was not apparent in the cases of long duration. Two patients with IgM antidisialosyl antibodies and cold agglutinating activity had a large fiber neuropathy with intermittent oculofacial involvement. Both responded to intravenous immunoglobulin. Findings in the remaining patients were varied. Recognition of IgM subgroups is important both for prognosis and possible response to treatment.

Waldenström's macroglobulinemia: clinical features, complications, and management

PURPOSE

To review the clinical features, complications, and treatment of Waldenström's macroglobulinemia, a low-grade lymphoproliferative disorder that produces monoclonal immunoglobulin (Ig) M.

METHODS

A review of published reports was facilitated by the use of a MEDLINE computer search and by manual search of the Index Medicus.

RESULTS

The clinical manifestations associated with Waldenström's macroglobulinemia can be classified according to those related to direct tumor infiltration, to the amount and specific properties of circulating IgM, and to the deposition of IgM in various tissues. Asymptomatic patients should be followed without treatment. For symptomatic patients, standard treatment consists primarily of oral chlorambucil; nucleoside analogs, such as fludarabine and cladribine, are effective in one third of previously treated patients and in up to 80% of previously untreated patients. Preliminary evidence suggests that anti-CD20 monoclonal antibody may be active in about 30% of previously treated patients and that high-dose therapy with autologous stem-cell rescue is effective in most patients, including some with resistance to nucleoside analogs.

CONCLUSION

Waldenström's macroglobulinemia has a wide clinical spectrum that practicing physicians need to recognize early to reach the correct diagnosis. When therapy is indicated, oral chlorambucil is the standard primary treatment, but cladribine or fludarabine can be used when a rapid cytoreduction is desirable. Prospective randomized trials are required to elucidate the impact of nucleoside analogs on patients' survival. A nucleoside analog is the treatment of choice for patients who have been previously treated with an alkylating agent.

Clinical features, evaluation, and treatment of patients with polyneuropathy associated with monoclonal gammopathy of undetermined significance (MGUS)

A number of common disorders of the peripheral nervous system are closely linked to a monoclonal gammopathy. In a minority of patients, the neuropathy represents the sentinel feature of a malignant plasma cell dyscrasia, such as multiple myeloma or its osteosclerotic variant, Waldenstrom's disease, amyloidosis, cryoglobulinemia or lymphoma; the vast majority have so-called "monoclonal gammopathy of undetermined significance" (MGUS). Sensory symptoms predominate with paresthesias, numbness, imbalance, and gait ataxia. Electrodiagnostic studies show mixed demyelinating and axonal features and often may be indistinguishable from findings in chronic inflammatory demyelinating polyneuropathy. Some have a pure axonal polyneuropathy, and in these patients the relationship to the paraprotein is less certain. With limited success, correlations have been made between the immunoglobulin type (IgM, IgG, or IgA) and the clinical and electromyographic characteristics of the neuropathy. The treatment of MGUS neuropathies poses a considerable challenge. Patients with IgG/IgA-MGUS have improved with corticosteroids or intravenous immune globulin. Only the benefit of plasma exchange has been substantiated in a controlled trial. The IgM neuropathies tend to be more refractory but often improve with similar regimens, particularly if cytotoxic agents are added in doses sufficient to reduce the amount of the M-protein. In addition to plasma exchange, chlorambucil, and cyclophosphamide, interferon-alpha is a novel therapy that holds promise for patients with IgM neuropathies associated with anti-myelin associated antibodies.

Paraproteinemia and neuropathy

Paraprotein-associated neuropathies are a diverse group of disorders. The pathogenesis of many of them is poorly understood. Treatments have usually consisted of plasma exchange, corticosteroids, intravenous immunoglobulin, and other immunosuppressive therapies. Response to treatment has varied from good to very poor. Most recent work in this field has had two goals: achieving a better understanding of pathogenesis and developing better treatments. Such diverse entities as hepatitis C virus, vascular endothelial growth factor, and cytokines now appear to play a role in pathogenesis. More aggressive therapies such a bone marrow transplantation, interferon-alpha, and Rituximab have shown some promise.

Anti-myelin-associated glycoprotein antibodies predict the development of neuropathy in asymptomatic patients with IgM monoclonal gammopathy

We examined 52 asymptomatic patients with IgM monoclonal gammopathy and correlated anti-myelin-associated glycoprotein (anti-MAG) IgM with the presence of subclinical neuropathy and, in 24 of these patients, with the development of symptomatic neuropathy during a follow-up interval of 40 to 144 months (mean, 75.3 months). Three of 6 patients (50%) with high (>1/6,400) anti-MAG IgM had subclinical neuropathy at entry compared with 2 of 46 patients (4.3%) with low or no reactivity. At follow-up, a symptomatic neuropathy occurred in 3 of 4 patients with high reactivity and in 3 of 21 patients with low or no reactivity. The correlation of high anti-MAG IgM with the presence of subclinical neuropathy or the development of symptomatic neuropathy supports its pathogenetic role in the neuropathy.

Myelinated dorsal root ganglion cultures activate both the alternative and classical pathways of complement

We used rat myelinated dorsal root ganglion (MDRG) cultures to study antibody and complement-mediated mechanisms of peripheral demyelinating diseases. Heat inactivated serum from a patient (LT) with peripheral neuropathy and a monoclonal IgM reactive with myelin-associated glycoprotein (anti-MAG) and sulfated glucuronosyl glycolipids (anti-SGGL) was used as an antibody source. Incubation of whole human serum (WHS) or WHS and anti-SGGL with MDRGs resulted in reduction of classical and alternative pathway hemolytic activities and the development of abnormal myelin sheaths. Incubation of MDRG cultures with C2-deficient serum showed activation of the alternative complement pathway. Classical pathway hemolytic activity was reduced when Factor B-depleted serum was incubated with MDRG cultures. The rat MDRG culture system provides a good model system of a peripheral nerve and has therefore been used by several investigators to study antibody and complement-mediated demyelination associated with peripheral neuropathies. However, our studies indicate a high degree of complement activation and membrane disruption of cultures incubated with WHS.

Variability in the binding of anti-MAG and anti-SGPG antibodies to target antigens in demyelinating neuropathy and IgM paraproteinemia

Densitometry of immunostained Western blots or thin layer chromatograms and enzyme-linked immunosorbent assays (ELISAs) were used to compare the relative strengths of IgM binding to myelin-associated glycoprotein (MAG), P0 glycoprotein, peripheral myelin protein-22 (PMP-22), sulfate-3-glucuronyl paragloboside (SGPG), and other potential target antigens in a series of eleven patients with sensory or sensorimotor demyelinating neuropathy and IgM paraproteinemia. The IgM from all patients exhibited reactivity with both MAG and SGPG, and there was a statistically significant correlation between the overlay assays and ELISAs for measuring the strength of IgM binding to MAG and to SGPG. However, the data revealed variations in the relative strengths with which the antibodies bound to the potential target antigens and heterogeneity in their fine specificities. First, there was a poor correlation between the strength of binding to MAG and to SGPG, respectively. Second, reactivity with MAG or SGPG in a few of the patients was only detected by one of the two assay systems. Third, about one-third of the patients' IgM absolutely required the sulfate on SGPG for reactivity, whereas the others retained some reactivity after removal of the sulfate. Fourth, IgM from two of the patients exhibited unusually strong reactivity with the proteins of compact myelin, P0 and PMP22. These relative differences in strengths of antibody binding to the potential antigens were compared with the patients' clinical presentations and with their responses to intravenous immunoglobulin (IVIg) therapy in a clinical trial in which they participated. For the most part, these variations did not correlate with clinical presentation, which was relatively homogeneous in this series of patients. However, an inverse relationship was noted between degree of reactivity to MAG by ELISA and response to IVIg. Two of the patients who responded had only mild elevations of IgM antibodies to nerve glycoconjugates and exhibited some unusual immunochemical and clinical characteristics in comparison to the other patients. The results demonstrate differences in the relative strengths with which anti-MAG and anti-SGPG IgM antibodies from different patients bind to potential neural target antigens which may affect pathogenic mechanisms and response to therapy.

Overproduction of vascular endothelial growth factor/vascular permeability factor is causative in Crow-Fukase (POEMS) syndrome

Crow-Fukase or POEMS syndrome of polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes is a rare multisystem disorder of obscure pathogenesis that is associated with microangiopathy, neovascularization, and accelerated vasopermeability. We examined the levels of the vascular endothelial growth factor/vascular permeability factor (VEGF) in the serum and cerebrospinal fluid (CSF) from 10 patients with this syndrome. Serum VEGF levels were about 15-30 times those in control subjects or patients with Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and other neurological disorders. The CSF VEGF levels, however, were similar to those found in GBS and CIDP. Elevated VEGF levels in the serum decreased in 7 patients with Crow-Fukase syndrome after conventional therapy. The principal isoform of VEGF in Crow-Fukase syndrome was VEGF165. Elevated VEGF was independent of M-protein. Our results suggest that the overproduction of VEGF is important in the pathogenesis of this disorder.

The role of glycosphingolipids in neurological disorders. Mechanisms of immune action

Specific criteria that are required for understanding the significance of glycosphingolipid (GSL) antibodies, as well as mechanisms that may underlie the immunopathogenesis of these disorders, are proposed. These criteria are illustrated by describing the role of a unique family of acidic GSLs, the sulfated glucuronosyl glycolipids (SGGLs), in the pathogenic mechanisms of peripheral neuropathy with IgM paraproteinemia. High anti-SGGL antibody titers are detected in patients suffering from this disorder. It is demonstrated that SGGLs, which possess a common carbohydrate epitope with myelin-associated glycoprotein (MAG), several low-molecular-weight glycoproteins in the PNS, and a number of cell adhesion molecules, are potential target antigens for the neuropathy. Evidence is provided that sensitization of laboratory animals with pure SGGLs elicits experimental peripheral neuropathies that exhibit remarkable similarities with respect to antibody specificity, and electrophysiological and pathological features to the human conditions. By intraneural injection of antibodies into the sciatic nerve of rats, it is demonstrated that pathological changes consisting of demyelination and axonal degeneration are mediated by an antibody- and complement-dependent process. To elucidate the mechanisms of antibody penetration from circulation into the endoneurial space, it is further shown that brain microvascular endothelial cells express SGGLs. Moreover it has been found that inflammatory cytokines are capable of upregulating the expression of SGGLs on the endothelial cell surface, resulting in a greater attachment of leukocytes. This latter observation suggests that SGGLs may also participate in cell-mediated responses in certain inflammatory neurological disorders.

Plasma-Exchange in Chronic Peripheral Neurological Disorders

We investigated 19 patients affected by chronic peripheral neurological disorders treated with therapeutic plasma exchange (TPE) to verify the efficacy of the therapeutic protocol used in these diseases.

Every patient was clinically considered after 5 TPE. Those who showed an improvement started chemotherapy and continued TPE at the rate of 2 procedures/week for 2 weeks, then 1 procedure/week for 1 month and finally 1 procedure every 2 weeks for 2 months. Intravenous immunoglobulins (IVIg) were infused at the end of apheretic treatment in one of the patients affected by neurological disorders due to monoclonal gammopathy undetermined significance. HCV-positive patients with cryoglobulins were treated with α-interferon (α-IFN) for 6 months before TPE.

Eleven patients (58%) had a symptomatic improvement, 2 (1.5%) stopped TPE treatment owing to side effects and 6 (31.5%) did not respond to apheretic therapy.

In order to improve the advantages of TPE we suggest using IVIg at the end of apheretic therapy, while in HCV-positive patients, at least one year of α-IFN therapy is required before initiating TPE.

The role of complement in disorders of the nervous system

The complement (C) system plays important roles in host defense but activation at inappropriate sites or to an excessive degree can cause host tissue damage. C has been implicated as a factor in the causation or propagation of tissue injury in numerous diseases. The brain is an immunologically isolated site, sheltered from circulating cells and proteins of the immune system; nevertheless, there is a growing body of evidence implicating C in numerous brain diseases. In this brief article we review the evidence suggesting a role for C in diseases of the central and peripheral nervous system and discuss the possible sources of C at these sites. Some brain cells synthesize C and also express specific receptors; some are exquisitely sensitive to the lytic effects of C. The evidence suggests that C synthesis and activation in the brain are important in immune defense at this site, but may also play a role in brain disease.

A randomised clinical trial comparing interferon-alpha and intravenous immunoglobulin in polyneuropathy associated with monoclonal IgM. The IgM-associated Polyneuropathy Study Group

OBJECTIVES

The polyneuropathy associated with a monoclonal IgM directed to the myelin associated glycoprotein (MAG) is a specific entity with a putative causal link between the IgM and the neuropathy. The small benefit offered by alkylating agents or plasma exchanges in these patients justifies the search for alternative treatments.

METHODS

A 12 month multicentre, prospective, randomised, open clinical trial was carried out comparing intravenous immunoglobulin (IVIg; 2g/kg and then 1 g/kg every three weeks) and recombinant interferon-alpha (IFN-alpha; 3 MU/m2 subcutaneously three times weekly). The main end point was a clinical neuropathy disability score (CNDS) after six months of treatment. Twenty patients were enrolled; 10 were assigned to IVIg and 10 to IFN-alpha.

RESULTS

At six months, one out of 10 patients treated with IVIg had a CNDS improvement of more than 20% whereas eight out of 10 patients treated with IFN-alpha had such an improvement (P=0.005). The mean CNDS worsened by 2.3 (SD 7.6) (8%) in the IVIg group whereas it improved by 7.5 (SD 11.1) (31%) in the IFN-alpha group (P=0.02). This improvement persisted after 12 months and was mainly related to an improvement of the sensory component (P=0.02) whereas the motor component was unchanged (P=0.39). Electrophysiological data did not show improvement of motor nerve conduction velocities whereas sensory nerve conduction velocities improved in the upper limbs. A decrease in the level of the monoclonal IgM was seen in two patients treated with IFN-alpha. At the end of the treatment, antibody activity to MAG was still detected in the serum of all patients.

CONCLUSION

IVIg, as used in this study, did not improve patients with polyneuropathy and monoclonal IgM. By contrast, although its mechanism of action remains to be fully elucidated, IFN-alpha was effective in eight out of 10 patients at six months.

A novel monoclonal antibody which reacts with a high molecular weight neuronal cytoplasmic protein and myelin basic protein (MBP) in a patient with macroglobulinemia

We report on the case of a 70-year-old man with primary macroglobulinemia who showed cranial polyneuropathy and extensive radiculoneuropathy. His serum contained an IgM lambda monoclonal antibody which reacted with both a high molecular weight protein in grey matter and purified myelin basic protein (MBP) on immunoblotting. In an immunohistochemical study, strong immunoreactivity was detected only in the cytoplasm of neurons and weak immunoreactivity was detected in myelin. These findings suggest that this antibody may be related to the pathogenesis of neuronal damage in patients with macroglobulinemia.

T-cell-mediated epineurial vasculitis and humoral-mediated microangiopathy in cryoglobulinemic neuropathy

We used immunohistochemistry to assess the role of humoral and cellular factors in endoneurial microangiopathy and epineurial vasculitis in 15 nerve biopsies of patients with axonal neuropathy and monoclonal or mixed cryoglobulinemia (CG). Deposition of immunoglobulins and cytolytic complement was detected in endoneurial capillaries of patients with mixed CG. Epineurial inflammatory infiltrates containing beta2-integrin-positive lymphocytes and monocytes surrounded arterioles expressing cell adhesion molecules, thus suggesting a cell-mediated pathogenesis of the epineurial vasculitis. On the other hand, the absence of immune complex deposition and polymorphonuclear elements suggests a minor role for the humoral mechanisms in the formation of the vasculitic lesions. This study indicates that both cell-mediated mechanisms and immune complexes/cryoglobulins are involved, although at different levels, in the pathogenesis of CG neuropathy.

A controlled study of intravenous immunoglobulin in demyelinating neuropathy with IgM gammopathy

Eleven patients with demyelinating polyneuropathy associated with monoclonal IgM antibodies were randomized to receive IVIg or placebo, monthly, for 3 months in a double-blind study. After a washout period, they crossed over to the alternate therapy. Response was gauged by evaluating muscle strength, sensation, and neuromuscular symptoms at baseline, after 3 months, and at treatment's end. After IVIg therapy, the strength improved in only 2 of 11 patients, by 28 and 38.5 points from baseline, and declined after placebo. In 1 other patient, the sensory score improved by 13 points. Antibody titers to MAG/SGPG or gangliosides did not appreciably change. We conclude that IVIg has only a modest benefit to not more than 18% of patients with IgM paraproteinemic demyelinating neuropathy.

Morphological changes at paranodes in IgM paraproteinaemic neuropathy

The paranode is one of a number of sites of a specific myelin sheath abnormality found in cases of IgM paraproteinaemic neuropathy. The gammopathy may be malignant or, more frequently, benign, and is often associated with a predominantly demyelinating neuropathy. The circulating paraprotein IgM antibody, usually with kappa light chains, was found in many cases to recognise an antigenic determinant in myelin, identified as myelin-associated glycoprotein (MAG). Other glycoconjugates expressed by Schwann cells may also be recognised by the antibody. MAG is localized to regions of the myelin sheath in which the membranes are uncompacted. The paranode is one such region, and there is evidence that IgM is deposited specifically on the membranes of the terminal loops of the myelin sheath in addition to other MAG-associated regions of the sheath. In many cases the presence of the paraprotein appears not to otherwise affect paranodal organization; in a few it is associated with changes to the termination of the loops on the axolemma and to the associated Schwann cell cytoplasm. These findings do not provide unambiguous evidence that binding of anti-MAG IgM antibodies at the paranode is a direct cause of demyelination. Whilst localization of the paraprotein closely matches that of MAG, proof is still lacking that the relevant antigen is MAG itself.

Osteosclerotic myeloma and 'POEMS' syndrome

Metabolic bone disease is a major cause of morbidity and mortality in patients suffering from multiple myeloma. This usually results from an imbalance between the osteoclast and osteoblast activity of bone resorption and formation due to the secretion of an osteoclast-activating factor by the myeloma cells. This generally takes the form of lytic lesions, hypercalcaemia and osteoporosis but, in a minority of patients, osteosclerosis is a striking feature. In a proportion of patients with gammopathy and the osteosclerotic form of the disease, there appears to be an association with other symptom complexes including Polyneuropathy, organomegaly, endocrine changes, and skin abnormalities. This article summarizes the clinical, radiological and laboratory features of this syndrome, which is known by the acronym 'POEMS'. It is important to recognize this condition, as it carries a better prognosis than the more common lytic form of the disease and because vincristine, and agents frequently used to treat this condition, may severely exacerbate the neuropathy and should be avoided. This syndrome is also important because it may give some insight into the pathophysiology of the plasma-cell dyscrasias.

Immune attack on the Schwann cell surface in acute inflammatory demyelinating polyneuropathy

The localization, mode of action, and roles of complement in the Guillain-Barre syndrome have been controversial. We used high-resolution immunocytochemistry to localize complement activation products in early stages of the acute inflammatory demyelinating polyneuropathy (AIDP) pattern of Guillain-Barre syndrome. Three AIDP subjects who were autopsied had had symptoms for 3 to 9 days at the time of death. Immunocytochemistry was performed on etched, epoxy resin-embedded sections, and the next thin section was compared by electron microscopy (thick/thin sections). Many fibers had a rim of the complement activation marker C3d and the terminal complement complex neoantigen C5b-9 along the outer surface of the Schwann cells. Ultrastructural analysis of these C3d-positive fibers showed mild vesicular changes of the outermost myelin lamellae. Vesicular degeneration was seen before the invasion of macrophages into the myelin, and was the predominant change in the subject with symptoms for 3 days. C3d staining was not found on myelin membranes. The results suggest that at least some forms of AIDP are complement mediated. We speculate that complement is activated by antibody bound to epitopes on the outer surface of the Schwann cell and that the resulting complement activation initiates the vesiculation of myelin.

Anti-MAG and anti-SGPG antibodies in neuropathy

We compared the binding of human antibodies from patients with neuropathy to the myelin-associated glycoprotein (MAG), to its cross-reactive glycolipid sulfoglucuronyl paragloboside (SGPG), and to sections of peripheral nerve. Titers were correlated with the clinical presentation and results of electrophysiological and pathological studies. Most patients had a predominantly sensory or sensorimotor demyelinating neuropathy and highly elevated antibodies to both MAG and SGPG, but 2 had highly elevated antibodies to MAG alone, and 1 to SGPG alone. Two patients had predominantly motor neuropathy and highly elevated antibodies to SGPG which reacted with MAG by Western blot but not by enzyme-linked immunosorbent assay. One patient had amyotrophic lateral sclerosis and antibodies to SGPG but not to MAG. These studies indicate that the neuropathic syndrome associated with anti-MAG or -SGPG antibodies are more heterogeneous than previously suspected, and that although most of the antibodies react with both MAG and SGPG, some may react with MAG or SGPG alone.

Sensitization of Lewis rats with sulfoglucuronosyl paragloboside: electrophysiological and immunological studies of an animal model of peripheral neuropathy

Antibodies against sulfoglucuronosyl glycosphingolipids (SGGLs) are known to be present in sera of patients with chronic polyneuropathy associated with IgM paraproteinemia. We recently studied rats sensitized with sulfoglucuronosyl paragloboside (SGPG), a major SGGL species, emulsified with keyhold limpet hemocyanin and Freund's adjuvant. The titer of the IgM class antibodies against SGPG increased up to 1:1,600, while that of the IgG class increased up to 1:800 2 weeks after sensitization. The antibodies showed a high degree of antigenic specificity; no cross-reactivity with other brain glycolipids could be detected. They, however, reacted with human myelin-associated glycoprotein (MAG) by Western blot analysis, but not with rat MAG. These animal models showed minor but clear clinical signs of neuropathy, consisting of mild tail muscle tone loss and walking disabilities. Electrophysiological examination of the sciatic nerves revealed nerve conduction abnormalities which consisted of conduction block and mild decrease in conduction velocity. Thus, our results support the concept that anti-SGPG antibodies may play an important pathogenetic role in this type of chronic neuropathy.

Neuropathies associated with monoclonal gammopathies

Approximately 10% of patients with idiopathic peripheral neuropathy have an associated serum monoclonal gammopathy or M-protein. This represents six times the incidence of M-proteins found in the general population. In 5% of idiopathic peripheral neuropathy patients the M-protein is associated with an identifiable plasma cell dyscrasia. Sclerotic myeloma is particularly important to recognize because treatment may result in amelioration of the neuropathy and remission of the tumor. Patients with primary systemic amyloidosis often have preferential small fiber involvement with a dissociated sensory loss and autonomic dysfunction. The nerve root infiltration of lymphoproliferative disorders may simulate a polyradiculoneuropathy. In cases without an identifiable cause for the M-protein, referred to as monoclonal gammopathy of undetermined significance (MGUS), the pathophysiologic basis for the neuropathy is poorly defined in most cases. A role for M-proteins with antibody activity to myelin-associated glycoprotein is provocative. This review summarizes current knowledge of this important group of disorders.

Systemic passive transfer studies using IgM monoclonal antibodies to sulfatide

We present a patient with benign IgM-gamma anti-Sulfatide (SUL) whose neuropathy was transferred in newborn rabbits. The patient's clinico-pathological picture of anti-SUL-associated demyelinating neuropathy is reported. The monoclonal IgM antibodies prepared by Tatum's method, that retained their biological activity, were passively transferred to newborn rabbits. The passive transfer produced demyelinating nerve lesions very similar to the donor antibody neuropathy. In experimental lesions we observed the human IgM anti-SUL antibodies binding to Schmidt-Lanterman incisures and nodes of Ranvier. We postulate that the myelin-specific and complement-dependent lesions observed in the peripheral nerve support the potential demyelinating role of anti-SUL antibodies. Moreover, the pattern of the antibody binding to the perineuronal sheath of satellite cells in dorsal root ganglia strengthen the hypothesis that anti-SUL antibodies may have a pathogenetic role in this sensorimotor syndrome.

Plasma exchange and chlorambucil in polyneuropathy associated with monoclonal IgM gammopathy. IgM-associated Polyneuropathy Study Group

The study compared chlorambucil alone with chlorambucil in combination with plasma exchange in patients with polyneuropathy associated with monoclonal IgM. Forty four patients were prospectively randomly assigned, in a comparative open trial, to receive either 0.1 mg/kg/day chlorambucil orally, for 12 months or chlorambucil associated with 15 courses of plasma exchange, during the first four months of treatment. They were evaluated by a neuropathy disability score and nerve conduction studies. No difference was found between the two treatment groups. The average neuropathy disability score improved by 2.1 points from baseline (21.0 to 18.9) in the chlorambucil group and by 1.8 points (20.4 to 18.6) in the chlorambucil + plasma exchange group (P = 0.70). The mean motor nerve conduction velocity decreased from 20.0 to 18.2 m/s in the chlorambucil group and increased from 20.5 to 22.5 m/s in the chlorambucil + plasma exchange group (P = 0.51). A slight improvement of the sensory component of the neuropathy disability score (from 10.5 to 8.3) was noted in both groups (P = 0.01). At the end of the study and according to self evaluation, 15 patients--eight from the chlorambucil group and seven from the chlorambucil + plasma exchange group--reported clinical improvement, whereas 15--eight from the chlorambucil group and seven from the chlorambucil + plasma exchange group--reported clinical worsening. Neuropathy remained stable in the others. Thus plasma exchange seemed to confer no additional benefit in the treatment of polyneuropathy associated with monoclonal IgM.

Avidity distribution of antibodies against peripheral nerve myelin in patients with polyneuropathy associated with IgM monoclonal gammopathy and in healthy controls

To elucidate the role and nature of antibodies against peripheral nerve myelin (PNM) we studied their avidity distribution. Twelve patients with demyelinating polyneuropathy associated with IgM monoclonal gammopathy were compared with 12 healthy blood donors previously found to have anti-PNM antibodies of IgM isotype. For comparison, the avidity distribution of IgM antibodies against the varicella zoster antigen in 10 patients with herpes zoster infection was also studied. Microtitre plates containing antibody bound to antigen were exposed to increasing concentrations of sodium thiocyanate (NaSCN) followed by an ELISA assay. NaSCN changes the ion strength and the pH, and thereby the critical conditions for antibody-antigen binding. Resistance to NaSCN was used as a measure of antibody avidity. Anti-PNM antibodies from patients with monoclonal gammopathy were of predominantly low avidity whereas antibodies from blood donors were of predominantly high avidity. Avidity index, representing the molar concentration of NaSCN required to reduce the initial absorbance values by 50%, was on average 11.7 times higher in blood donors (range 0.24-2.65, mean = 0.82) than in patients with monoclonal gammopathy (range 0.04-0.10, mean = 0.07) (p = 0.002). On the other hand, patients with monoclonal gammopathy had on average a 100-fold higher relative concentration of antibodies against PNM compared to blood donors (range 4.1-392.6 AU, mean 85.0 AU, and range 0.2-1.7 AU, mean 0.85 AU, respectively) (p = 0.002). Antibodies against the varicella zoster antigen from patients with herpes zoster showed a high avidity index (range 0.25-2.6, mean = 1.24). Using Western blot, several 14-30 kDa proteins in PNM were found to be the target antigen for IgM anti-PNM antibodies in both patients with monoclonal gammopathy and polyneuropathy, and in blood donors.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis and therapy of neuropathies associated with monoclonal gammopathies

Approximately 10% of patients with peripheral neuropathy of otherwise unknown etiology have an associated monoclonal gammopathy. Both the neuropathies and the monoclonal gammopathies in these patients are heterogeneous, but several distinct clinical syndromes that may respond to specific therapies can be recognized. It is important to recognize these syndromes because monoclonal gammopathies also occur in 1% of the normal adult population, and in some cases, monoclonal gammopathies are coincidental and unrelated to the neuropathy. In patients with IgM monoclonal gammopathies, IgM M proteins frequently have autoantibody activity and are implicated in the pathogenesis of the neuropathy. IgM M proteins that bind to myelin-associated glycoprotein (MAG) have been shown to cause demyelinating peripheral neuropathy; anti-GM1 antibody activity is associated with predominantly motor neuropathy, and anti-sulfatide or chondroitin sulfate antibodies are associated with sensory neuropathy. The IgM monoclonal gammopathies may be malignant or nonmalignant, and polyclonal antibodies with the same specificities are associated with similar clinical presentations in the absence of monoclonal gammopathy. IgG or IgA monoclonal gammopathies are associated with neuropathy in patients with osteosclerotic myeloma or the POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy myeloma, and skin changes). Amyloidosis or cryoglobulinemic neuropathies can occur with either IgM or IgG and IgA monoclonal gammopathies. Therapeutic intervention depends on the specific clinical syndrome but is generally directed at removing the autoantibodies, reducing the number of monoclonal B cells, and interfering with the effector mechanisms.

Frequency and clinical correlates of anti-neural IgM antibodies in neuropathy associated with IgM monoclonal gammopathy

We studied the frequency and clinical correlates of different IgM specificities in 75 patients with neuropathy associated with IgM monoclonal gammopathy. Patients were tested for IgM reactivity with the myelin-associated glycoprotein, P0, neurofilaments, and tubulin by immunoblot; with GM1, asialo-GM1, GM2, GD1a, GD1b, sulfatide, and chondroitin sulfate C by enzyme-linked immunosorbent assay; and with brain and nerve glycolipids by overlay high-performance thin-layer chromatography. Forty-two patients (56%) had high titers of IgM antibodies to MAG; 4 (5%), to sulfatide (1 also to myelin-associated glycoprotein); 4 (5%), to the 200-kd neurofilament (2 also to myelin-associated protein); and 1 each, to GD1b and chondroitin sulfate C. No reactivity was found in 26 patients (35%). More patients with anti-myelin-associated glycoprotein IgM (62%) than with unknown IgM reactivity (31%) had a predominantly sensory neuropathy (p < 0.025). Nerve conduction findings were consistent with a demyelinating neuropathy in 77% of patients reactive to myelin-associated glycoprotein and 24% with unknown reactivity (p < 0.0001) and the mean conduction velocity of peroneal nerve was lower in the former group (22.9 m/sec) than in the latter group (39.6 m/sec) (p < 0.000001). Patients with anti-sulfatide IgM had a sensorimotor neuropathy with morphological evidence of demyelination while anti-neurofilament IgM was not associated with homogeneous findings. Patients with anti-GD1b or anti-chondroitin sulfate C IgM had a predominantly motor impairment. The frequent occurrence of anti-neural IgM antibodies in neuropathy associated with IgM gammopathy, and their frequent, though not constant association with similar neuropathy features, support their possible pathogenetic role in the neuropathy.

Monoclonal IgM from patients with peripheral demyelinating neuropathies cross-react with bacterial polypeptides

Human monoclonal IgM associated with a demyelinating peripheral neuropathy often feature a distinct antibody activity directed against a glucuronyl sulphate epitope shared by myelin-associated glycoprotein (MAG), nerve glycolipids and low molecular weight peripheral nerve polypeptides. Earlier studies showed that these IgM use a diverse repertoire of VH and VL genes which exhibit somatic mutations, possibly indicative of an antigen-driven process. Here, we investigated whether such monoclonal IgM may react with environmental bacterial antigens. We found that six patients' sera and purified monoclonal IgM, as well as IgM from supernatants of three clonal anti-MAG-secreting cell lines reacted with unique 90-100 kD polypeptides from extracts of two out of 10 bacterial species. Purified MAG was able to inhibit this reactivity. These results indicate molecular mimicry as a possible mechanism of this immunomediated neuropathy and associated clonal lymphoid disease.

Widenings of the myelin lamellae in a typical Guillain-Barré syndrome

The so-called "widening of the myelin lamellae" are thought to be specific ultrastructural features of peripheral nerve myelin in patients with peripheral neuropathy associated with a monoclonal dysglobulinemia of IgM type and antiglycolipid activity. We report here a case of Guillain-Barré syndrome with no evidence of serum monoclonal dysglobulinemia, presenting the typical widenings of the myelin lamellae in small-diameter myelinated fibers from a sural nerve biopsy. In view of the positive reaction with anti-C3d complement on direct immunofluorescence, an immunological mechanism may be involved in the widenings of the myelin lamellae.

Plasma exchange and intravenous immunoglobulin treatment of neuromuscular disease

Removal of immunoglobulin by plasma exchange and administration of immunoglobulin by intravenous infusion each improve selected neuromuscular diseases. Both treatments are expensive and relatively brief in their duration of action, but they benefit both self-limited neuromuscular diseases such as the Guillain-Barré syndrome and acute exacerbations of more chronic neuromuscular diseases including myasthenia gravis and chronic inflammatory demyelinating polyneuropathy. It is likely that plasma exchange acts by removing pathogenic antibodies. The mechanism by which intravenous immunoglobulin acts is less clear. Possibilities include (1) antiidiotypic antibody effect, (2) complement absorption, (3) downregulation of immunoglobulin production, (4) receptor blockade, (5) virus neutralization, (6) enhancement of suppressor cells, and (7) inhibition of lymphocyte proliferation. Although plasma exchange and intravenous immunoglobulin have major side effects, severe reactions are uncommon with plasma exchange and rare with intravenous immunoglobulin. Because of their low incidence of life-threatening complications, both treatments have major appeal to clinicians. Because of their brief action and high cost as well as the uncertainty as to whether either or both should be employed, their role in the therapeutic armamentarium of the neurologist requires further study.

Polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy and skin changes (POEMS) syndrome

A patient with a three year history of POEMS syndrome-polyneuropathy, hepatosplenomegaly M-protein, skin changes, optic disc edema, peripheral oedema, pleuritis, lymphadenopathy, and osteosclerotic myeloma is described. The patient had a twenty year history of psoriasis and impotence was the first sign of the disease. The pathophysiology of this multisystem disorder is unknown, although the M-protein is essential. No improvement was found after radiation, chemotherapy and steroid treatment.

Schnitzler's syndrome associated with sensorimotor neuropathy

We describe a patient with chronic urticaria in association with monoclonal IgM gammopathy (Schnitzler's syndrome). Seven years after the onset of the cutaneous lesions sensorimotor neuropathy developed. Myelin-associated glycoprotein was detected in the patient's serum. High doses of corticosteroids improved the skin condition but failed to prevent the neuropathy. Six months of treatment with immunoglobulins was without benefit.

Peripheral neuropathy in IgM monoclonal gammopathy and Wäldenstrom's macroglobulinemia: a frequent complication in elderly males with low MAG-reactive serum monoclonal component

Peripheral neuropathy (PN) is a frequent complication during primary macroglobulinemia (PM), whose immunological genesis has been suggested by various authors. This study involved 65 PM patients (44 men and 21 women aged 35-78), diagnostically divided into MGUS (31 cases), and indolent (IWM, 24 cases) or symptomatic (WM, 10 cases) Waldenstrom macroglobulinemia groups. All patients underwent neurological examination, including electrodiagnostic evaluation and the determination of the serum titre of antimyelin-associated glycoprotein (MAG). An evaluation was made of the prevalence of PN and its correlation with a series of hematological variables. The prevalence of PN was 31.6%: of those with PN, 73.1% manifested both clinical and electrophysiological signs of PN, primarily of the demyelinating type. Significant correlations emerged between the presence of PN and sex (M vs. F P = 0.0001), advanced age (P = 0.049), low MC levels (P = 0.025), high anti-MAG titres (P = 0.001) and high Hb levels (P = 0.001). No significant correlation with the diagnostic definition of PM was found, although the majority of cases with (particularly demyelinating) PN were MGUS or IWM. At multivariate analysis, the presence of PN significantly correlated with sex (P = 0.0001), age (P = 0.019), and anti-MAG titre (P = 0.001). Ten of the 26 PN cases showed no MAG reactivity. Significant correlations between PN and low serum MC levels/high MAG reactivity support the hypothesis of the antibody-mediated origin of many PN, and that the presence of PN depends on the characteristics of the proliferating pathological B clone, rather than on the tumor burden of the form of macroglobulinemia. Clinically, our data reconfirm the frequency of PN during PM and indicate simple clinicohematological variables useful for identifying patients at high neuropathic risk.

Reactivity of a human monoclonal anti-GM1 and anti-GD1b IgM antibody with human neurons in cultures

A serum containing a monoclonal IgM lambda with anti-GM1 and anti-GD1b activity was obtained from a patient with upper motor neuron syndrome. By indirect immunocytochemical techniques with double staining, the patient's IgM strongly stained membranes of neurons in primary cultures of fetal central and peripheral nervous system. It was cytotoxic for neurons in two human neuroblastoma established cell lines in a complement-dependent chromium release assay. These results are in keeping with the hypothesis of a direct pathogenetic role of such monoclonal anti-GM1 and GD1b IgM antibodies.

Human peripheral nerve macrophages in normal and pathological conditions

We investigated, by immunocytochemistry and immune electron microscopy, the immunophenotype, morphology and functional properties of human peripheral nervous system (PNS) macrophages (M phi) under normal and pathological conditions. Endoneurial M phi disclosed an elongated, ramified morphology, with the main processes oriented along the major axis of nerve fibers; they shared several lineage-related and functional markers with monocyte/macrophages and central nervous system (CNS) microglia, including CD4, CR3, CR4 and FcRIII. In addition, basal expression of HLA-DR antigens was exclusively confined to M phi in normal PNS. In the course of unrelated pathological conditions, resident M phi underwent activation with transformation to hypertrophic cells or foamy phagocytes and up-regulation of the markers expressed in normal conditions; new expression of a macrophagic antigen was detected on activated M phi. In different neuropathies, HLA-DR expression was also detected on non-myelin forming Schwann cells with ultrastructural features indicative of denervation. The present results demonstrate that the human PNS is provided with an intrinsic population of immunocompetent and potentially phagocytic M phi, which represent the peripheral counterpart of CNS microglia.

Immunoelectron microscopic localization of monoclonal IgM antibodies in gammopathy associated with peripheral demyelinative neuropathy

A sural nerve biopsy from a patient with benign monoclonal IgM kappa gammopathy and sensory-motor demyelinative neuropathy, revealed marked loss of myelinated fibers and focal axonal degeneration as well as widespread demyelination and remyelination with onion-skin formation. Almost all myelinated fibers displayed characteristic widening of the myelin lamellae as well as excessive thickness and/or exuberant outfoldings of myelin, reminiscent of that seen in tomaculous neuropathy. Many endoneurial capillaries were lined by fenestrated endothelium, indicating breakdown of a normal blood-nerve barrier. The endoneurium contained large amounts of extracellular proteinaceous material. Immunofluorescence and immunoelectron microscopy performed on the nerve of the patient, demonstrated selective deposition of IgM kappa gammaglobulin, exclusively in the areas of splittings of the myelin lamellae. Schwann cells contained cytoplasmic myelin debris labelled with IgM kappa only. In the indirect immunofluorescence and immunoelectron microscopy, serum of the patient reacted with the whole thickness of compact peripheral myelin of a normal human nerve. There was no immunoreactivity with the central myelin, Schwannoma cells, glial cells, axons or neurons. Demonstration of the selective presence of monoclonal IgM in widened lamellae of myelinated fibers, as well as bound to the internalized myelin debris in Schwann cells and macrophages, indicates a pathogenetic role of monoclonal paraprotein in myelin injury. Demyelination is promoted by development of endothelial fenestrations in the endoneurial capillaries and breakdown of the blood-nerve barrier.