Axonal attenuation and secondary segmental demyelination in myeloma neuropathies

Management of Adverse Events and Supportive Therapy in Relapsed/Refractory Multiple Myeloma

Simple Summary

Multiple myeloma (MM) patients with relapsing and/or refractory (RR) disease are exposed for a prolonged time to multiple drugs, which increase the risk of toxicity. In addition to tumor response, preserving the quality of life represents an important goal for this patient population. Therefore, supportive therapy plays a pivotal role in their treatment by limiting disease- and drug-related complications. The aim of this review is to outline current standards and future strategies to prevent and treat renal insufficiency, anemia, bone disease, and infection, including COVID-19, in RRMM patients. In addition, the incidence and treatment of side effects of novel anti-MM agents will be discussed.

Abstract

Relapsed/refractory (RR) multiple myeloma (MM) patients are a fragile population because of prolonged drug exposure and advanced age. Preserving a good quality of life is of high priority for these patients and the treatment of disease- and treatment-related complications plays a key role in their management. By preventing and limiting MM-induced complications, supportive care improves patients’ outcome. Erythropoietin-stimulating agents and bisphosphonates are well-established supportive strategies, yet novel agents are under investigation, such as anabolic bone agents and activin receptor-like kinase (ALK) inhibitors. The recent dramatic changes in the treatment landscape of MM pose an additional challenge for the routine care of RRMM patients. Multidrug combinations in first and later lines increase the risk for long-lasting toxicities, including adverse cardiovascular and neurological events. Moreover, recently approved first-in-class drugs have unique side-effect profiles, such as ocular toxicity of belantamab mafodotin or gastrointestinal toxicity of selinexor. This review discusses current standards in supportive treatment of RRMM patients, including recommendations in light of the recent SARS-CoV-19 pandemic, and critically looks at the incidence and management of side effects of standard as well as next generation anti-MM agents.

Paranodal dissection in chronic inflammatory demyelinating polyneuropathy with anti-neurofascin-155 and anti-contactin-1 antibodies

OBJECTIVE

To investigate the morphological features of chronic inflammatory demyelinating polyneuropathy (CIDP) with autoantibodies directed against paranodal junctional molecules, particularly focusing on the fine structures of the paranodes.

METHODS

We assessed sural nerve biopsy specimens obtained from 9 patients with CIDP with anti-neurofascin-155 antibodies and 1 patient with anti-contactin-1 antibodies. 13 patients with CIDP without these antibodies were also examined to compare pathological findings.

RESULTS

Characteristic light and electron microscopy findings in transverse sections from patients with anti-neurofascin-155 and anti-contactin-1 antibodies indicated a slight reduction in myelinated fibre density, with scattered myelin ovoids, and the absence of macrophage-mediated demyelination or onion bulbs. Teased-fibre preparations revealed that segmental demyelination tended to be found in patients with relatively higher frequencies of axonal degeneration and was tandemly found at consecutive nodes of Ranvier in a single fibre. Assessment of longitudinal sections by electron microscopy revealed that detachment of terminal myelin loops from the axolemma was frequently found at the paranode in patients with anti-neurofascin-155 and anti-contactin-1 antibody-positive CIDP compared with patients with antibody-negative CIDP. Patients with anti-neurofascin-155 antibodies showed a positive correlation between the frequencies of axo-glial detachment at the paranode and axonal degeneration, as assessed by teased-fibre preparations (p<0.05).

CONCLUSIONS

Paranodal dissection without classical macrophage-mediated demyelination is the characteristic feature of patients with CIDP with autoantibodies to paranodal axo-glial junctional molecules.

Diagnosis and management of neuropathies associated with plasma cell dyscrasias

Neuropathies associated with plasma cell dyscrasias are a major cause of morbidity for patients managed by medical oncologists. Because of similarities in clinical presentation and on nerve conduction studies, identifying the underlying disease leading to a paraproteinemic neuropathy can often be difficult. In addition, the degree of neurologic deficit does not strictly correlate with the extent of abnormalities on common clinical laboratory testing. Fortunately, with increasing understanding into the biologic mechanisms of underlying hematologic diseases, additional biomarkers have recently been developed, thus improving our diagnostic capacity. Neuropathies associated with plasma cells dyscrasias are seen with Monoclonal gammopathy of undetermined significance (MGUS) particularly IgM subtype, followed by IgG and IgA MGUS, multiple myeloma, Waldenström's macroglobulinemia, amyloid, Castleman's disease, and POEMS syndrome. The mechanisms of neuronal injury associated with plasma cell dyscrasia vary based on underlying diagnosis and include malignant infiltration, immune-mediated antibody deposition, or local compression of nerve roots. The polyneuropathies are frequently demyelinating, although axonal and mixed neuropathies can also be seen. As demonstrated by the cases included in this review, patients frequently present with symmetric sensory disturbance, followed by progressive motor weakness. Unfortunately, because of the complexity of diagnostic testing, patients are frequently examined late, often after receiving several ineffective therapies. The aim of this case-based review is to provide clinicians with insight on how to properly recognize these atypical neuropathies and send the appropriate diagnostic work, increasing the likelihood of accurately classify the patient's underlying hematologic disorder.

Uncompacted Myelin Lamellae and Nodal Ion Channel Disruption in POEMS Syndrome

To elucidate the significance of uncompacted myelin lamellae (UML) and ion channel disruption at the nodes of Ranvier in the polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes (POEMS) syndrome, we evaluated sural nerve biopsy specimens from 33 patients with POEMS syndrome and from 7 control patients. Uncompacted myelin lamellae distribution was assessed by electron microscopy and immunofluorescence microscopy. In the POEMS patient biopsies, UML were seen more frequently in small versus large myelinated fibers. Paranodes and Schmidt-Lanterman incisures, where normal physiologic UM is located, were frequently associated with UM. Widening of the nodes of Ranvier (i.e. segmental demyelination) was not associated with UML. There was axonal hollowing with neurofilament condensation at Schmidt-Lanterman incisures with abnormal UML, suggesting axonal damage at those sites in the POEMS patient biopsies. Myelin sheath irregularity was conspicuous in large myelinated fibers and was associated with abnormally widened bizarrely shaped Schmidt-Lanterman incisures. Indirect immunofluorescent studies revealed abnormalities of sodium (pan sodium) and potassium (KCNQ2) channels, even at nonwidened nodes of Ranvier. Thus, UML was not apparently associated with segmental demyelination but seemed to be associated with axonal damage. These observations suggest that nodal ion channel disruption may be associated with functional deficits in POEMS syndrome patient nerves.

Multifocal motor neuropathy

Multifocal motor neuropathy (MMN) was first described in 1988 as a purely motor neuropathy affecting multiple motor nerves. The diagnosis was based entirely on demonstrating electrophysiological evidence of a conduction block (CB) that selectively affected motor axons, with sparing of sensory axons even through the site of motor CB. Subsequently, a similar disorder was reported but with absence of demonstrable CB on routine nerve conduction studies and there is still some debate as to whether MMN without CB is related to MMN. MMN is thought to be an inflammatory neuropathy related to an immune attack on motor nerves. The conventional hypothesis is that the primary pathology is segmental demyelination, but recent research raises the possibility of a primary axonopathy. Anti-GM1 antibodies can be found in some patients but it is unclear whether these antibodies are pathogenic. Intravenous immunoglobulin is the mainstay of treatment but other immunosuppressive treatments can also be effective.

Paraproteinemic neuropathy

Paraproteinemia frequently is associated with peripheral neuropathy. The clinical manifestations can be protean owing to the potential for multiple organ involvement. A methodical diagnostic approach to patients who have a plasma cell dyscrasia and neuropathy is necessary to ensure the appropriate detection of more widespread systemic involvement.

Neurological aspects of multiple myeloma and related disorders

The spectrum of neurologic complications of multiple myeloma (MM) and related conditions is as diverse as the conditions themselves. Complications range from direct compression (radiculopathy, spinal cord compression, base-of-the-skull tumor) to the infiltrative (amyloid, peripheral neuropathies, and numb chin syndrome of myeloma), the metabolic (slowed mentation from hyperviscosity, hypercalcemia, or uremia), and to autoimmune or cytokine-mediated (peripheral neuropathy). The two most common presentations are the compressive radiculopathy one sees in multiple myeloma and the peripheral neuropathies associated with many of the other disorders. The authors will review the neurologic complications of MM, monoclonal gammopathy of undetermined significance (MGUS), Waldenström macroglobulinemia (WM), POEMS syndrome, amyloidosis, and cryoglobulinemia.

Le syndrome POEMS (ou syndrome de Crow-Fukase)

POEMS is an acronym for polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes. POEMS syndrome is also called Crow-Fukase syndrome, chiefly in Japan. The 5 above mentioned features are not always present at the first examination. The minimal criteria to establish the diagnosis are the presence of a demyelinating and axonal polyneuropathy associated with an IgA or IgG monoclonal gammopathy, the light chain being almost always lambda, and at least 2 of the 8 other features: sclerosing plasmocytoma, endocrinopathy, skin changes, organomegaly, Castleman's disease, anasarca, papillary edema or thrombocytosis. Among these features, only cutaneous glomeruloid angioma are specific. Ultrastructural identification of uncompacted myelin lamellae on the peripheral nerve biopsy is also a strong argument in favor of the diagnosis. An associated "osteosclerotic" bone lesion must be carefully searched, because its treatment may improve the other features of the syndrome, especially the neuropathy. Cytokines and the vascular growth endothelial factor might play a role in the pathogenesis of this rare multisystemic disorder.

Alcoholic neuropathy is clinicopathologically distinct from thiamine-deficiency neuropathy

Characteristics of alcoholic neuropathy have been obscured by difficulty in isolating them from features of thiamine-deficiency neuropathy. We assessed 64 patients with alcoholic neuropathy including subgroups without (ALN) and with (ALN-TD) coexisting thiamine deficiency. Thirty-two patients with nonalcoholic thiamine-deficiency neuropathy (TDN) also were investigated for comparison. In ALN, clinical symptoms were sensory-dominant and slowly progressive, predominantly impairing superficial sensation (especially nociception) with pain or painful burning sensation. In TDN, most cases manifested a motor-dominant and acutely progressive pattern, with impairment of both superficial and deep sensation. Small-fiber-predominant axonal loss in sural nerve specimens was characteristic of ALN, especially with a short history of neuropathy; long history was associated with regenerating small fibers. Large-fiber-predominant axonal loss predominated in TDN. Subperineurial edema was more prominent in TDN, whereas segmental de/remyelination resulting from widening of consecutive nodes of Ranvier was more frequent in ALN. Myelin irregularity was greater in ALN. ALN-TD showed a variable mixture of these features in ALN and TDN. We concluded that pure-form of alcoholic neuropathy (ALN) was distinct from pure-form of thiamine-deficiency neuropathy (TDN), supporting the view that alcoholic neuropathy can be caused by direct toxic effect of ethanol or its metabolites. However, features of alcoholic neuropathy is influenced by concomitant thiamine-deficiency state, having so far caused the obscure clinicopathological entity of alcoholic neuropathy.

Patterns of nerve conduction abnormalities in POEMS syndrome

Polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes (POEMS) syndrome is a rare cause of demyelinating and axonal neuropathy. POEMS syndrome and chronic inflammatory demyelinating polyneuropathy (CIDP) cause peripheral nerve demyelination, and the electrodiagnostic findings may therefore be similar, but the two disorders are distinct. To elucidate the electrodiagnostic features of POEMS syndrome, we reviewed nerve conduction studies of 8 patients, and compared their results with those in 42 patients with CIDP. The patients with POEMS syndrome showed (1) slowing of nerve conduction that was more predominant in the intermediate than distal nerve segments, (2) rare conduction block (6% of the tested nerves), and (3) more severe attenuation of compound muscle action potentials in the lower than upper limbs. Findings in the CIDP patients were characterized by multifocal conduction slowing that was occasionally dominant distally, frequent conduction block (44% of tested nerves), and less discrepancy between upper and lower limb nerves. The pattern of nerve conduction abnormalities differs between these disorders. Recognition of these typical patterns may be helpful for early diagnosis of POEMS syndrome.

Complications and supportive therapy of multiple myeloma

The clinical spectrum of MM is variable. Infiltration of bone and bone marrow by malignant plasma cells results in severe osteopenia, lytic lesions, pathological fractures and anaemia. Occasionally, significant numbers of plasma cells circulate in the bloodstream. Hypercalcaemia and Bence Jones proteinuria are the main reasons for renal impairment, but amyloidosis and monoclonal immunoglobulin deposition should also be considered. Neurological impairment is most often due to spinal cord pressure by an extradural plasma cell tumour. In some patients, symptoms and signs of peripheral neuropathy may be present. Amyloidosis complicates the course of a minority of patients with MM and further impairs the performance of affected patients. Circulating monoclonal protein may increase serum viscosity, impair the function of platelets and coagulation factors, and behave as a cryoglobulin. The levels of uninvolved immunoglobulins are usually decreased, rendering patients susceptible to various bacterial infections. One or more of these complications provides a clue for the diagnosis, forms the basis for defining prognosis and must be managed expeditiously and concurrently, with the institution of specific treatment for the myeloma.

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.

Smaller axon and unaltered numbers of microtubules per axon in relation to number of myelin lamellae of myelinated fibers in the mutant quail deficient in neurofilaments

To characterize the morphological features of the myelinated fibers in the mutant quails deficient in neurofilaments (NF), caused by a nonsense mutation in the NF-L gene, the morphological parameters of the axon and myelin sheath, and their relationships in the peroneal nerve were evaluated. In the mutant, the axonal area was smaller than in the control (P > 0.01), reflecting the lack of large diameter axons. There was no significant difference in the mean number of myelin lamellae and of their spacings between controls and mutants. Therefore, it was decided to analyze the alteration of axonal parameters in relation to the number of myelin lamellae. In the regression analysis, the number of microtubules (MT) per square micrometer of the axonal area was greater in the mutant than in the control (P < 0.05); however, the number of MT per axon was similar in controls and mutants with the same given number of myelin lamellae. The number of MT+NF per axon was smaller in the mutant than in the control only for myelinated fibers with more than 25 myelin lamellae (P > 0.05). These findings indicate that there was a less significant effect of NF deficiency on the smaller than on the larger myelinated fibers. There was no compensatory increase in the numbers of MT per axon of the myelinated fibers in the mutant as found previously in the unmyelinated fibers of the mutant.

POEMS syndrome: a study of 25 cases and a review of the literature. French Study Group on POEMS Syndrome

OBJECTIVE

To determine whether there are peculiarities of the POEMS syndrome (a multisystemic disorder associated with polyneuropathy, organomegaly, endocrinopathy of various forms, production of a monoclonal [M] component, and skin changes) in Caucasian patients, especially signs and symptoms absent in other series; and to attempt a reappraisal of the neuropathy and endocrinopathy to find a unifying mechanism.

DESIGN

A retrospective, cooperative study compared 25 cases, observed over a 15-year period, with two published series of patients, one of Japanese patients and one of American patients, and with a review of the literature on non-Asian cases. Details were obtained of patients' medical history, physical examination, immunochemical and hormonal testing, roentgenographic examination, computed tomography imaging, and electromyography.

RESULTS

The main features of the syndrome found in these patients were those first described in Japan: polyneuropathy, enlargement of the lymph nodes, liver, and spleen, endocrine disturbances, low concentration of the monoclonal component, hyperpigmentation, and hypertrichosis. Three other symptoms were found more frequently than previously reported: skin angiomas, scleroderma changes of the hands, and thrombocytosis. Electromyography and nerve biopsy showed a variety of abnormalities ranging from demyelination to axonal degeneration. Nerve deposits of immunoglobulin were absent. Organomegaly seemed to be heterogeneous. Pathologic findings in the enlarged lymph nodes and spleen were compatible with Castleman's disease. Liver biopsies were usually normal. The endocrine changes were surprisingly diverse, with some observations combining unrelated primary and secondary insufficiencies. No single hypothesis emerged regarding their mechanism. All M components had a lambda-light chain. An IgG M component was found more frequently in solitary lesions. An IgA M component was found more frequently in patients without bone lesions. Sedimentation rate was usually normal. Radiotherapy of solitary plasma-cytomas was followed by dramatic improvement of extramedullary signs and symptoms in all cases.

CONCLUSIONS

The symptoms, clinical course, and management of the patients reported here were similar to those observed in the literature. This study confirms the existence of a close link between symptoms and lambda-light-chain production. There are indications that a plasma cell growth factor that does not cross-react with interleukin-6 (IL-6) may be involved.

Imaging myelinated nerve fibres by confocal fluorescence microscopy: individual fibres in whole nerve trunks traced through multiple consecutive internodes

Current methods of morphological analysis do not permit detailed imaging of individual myelinated fibres over substantial lengths without disruption of neighbouring, potentially significant, cellular and extracellular relationships. We report a new method which overcomes this limitation by combining aldehyde-induced fluorescence with confocal microscopy. Myelin fluorescence was intense relative to that from other tissue components, enabling individual myelinated nerve fibres to be traced for distances of many millimeters in whole PNS nerve trunks. Image obtained with a Bio-Rad MRC-600 confocal laser scanning microscope clearly displayed features of PNS and CNS myelinated fibres including nodes of Ranvier; fibre diameter; sheath thickness and contour; branch points at nodes; as well as (in the PNS) Schmidt-Lanterman incisures and the position of Schwann cell nuclei. Direct comparisons using the same specimens (whole nerve trunks; also teased fibres) showed confocal imaging to be markedly superior to conventional fluorescence microscopy in terms of contrast, apparent resolution and resistance to photobleaching. Development of the fluorophore was examined systemically in sciatic nerves of young adult rats. In separate experiments, animals were perfused systemically using (1) 5% glutaraldehyde; (2) Karnovsky's solution; (3) 4% paraformaldehyde; buffered with either 0.1 M sodium phosphate or sodium cacodylate (pH 7.4). The concentration of glutaraldehyde in the fixative solution was the principal determinant of fluorescence intensity. Confocal imaging was achieved immediately following perfusion with 5% glutaraldehyde or Karnovsky's. Fluorescence intensity increased markedly during overnight storage in these fixatives and continued to increase during subsequent storage in buffer alone. The fluorophore was stable and resistant to fading during storage (15 months at least), enabling data collection over extended periods. To demonstrate application of the method in neuropathology, individual fibres in transected sciatic nerve trunks were traced through multiple successive internodes: Classical features of Wallerian degeneration (axonal swelling and debris; ovoid formation and incisure changes; variation among fibres in the extent of degeneration) were displayed. The method is compatible with subsequent ultrastructural examination and will complement existing methods of investigation of myelinated fibre anatomy and pathology, particularly where preservation of 3-dimensional relationships or elucidation of spatial gradients are required.

Uncompacted myelin lamellae in polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes syndrome. Ultrastructural study of peripheral nerve biopsy from 22 patients

Mechanisms of peripheral neuropathies in polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes (POEMS) syndrome are poorly understood. A peripheral nerve biopsy was performed in 22 patients. Of these 9 had histological features of Castleman's disease on lymph node biopsies, and 19 had a monoclonal lambda light chain in their serum. Certain nerve fragments were paraffin embedded, others were frozen and studied by direct immunofluorescence, and others were fixed for ultrastructural examination. Paraffin-embedded fragments did not show any amyloid deposits, and at direct immunofluorescence there was no immunoglobulin fixation. At ultrastructural examination, features of uncompacted myelin lamellae (UML) were present in 19 patients, and their frequency varied from 1% to 16% of myelinated fibres. Up to now UML have been reported only in 7 patients with POEMS syndrome in the literature. UML have also been noticed in a few cases of inflammatory demyelinating polyradiculoneuritis and inherited tendency to pressure palsy.

Peripheral neuropathies associated with monoclonal proteins

Peripheral neuropathies associated with monoclonal proteins have received considerable attention as a clinically important group of chronic late-onset neuropathies. When a monoclonal protein is found in patients with peripheral neuropathy of unknown cause, as occurs in 10% of such cases, usually no associated disease is discovered; hence MGUS. Less often, disorders such as multiple myeloma, AL amyloidosis, Waldenström's macroglobulinemia, osteosclerotic myeloma, and lymphoma are found. Demyelinating neuropathies associated with MGUS of all classes, but particularly IgM, Waldenström's macroglobulinemia, and osteosclerotic myeloma typically follow an indolently progressive course, and frequently respond to treatments aimed at interfering with putative underlying immune mechanisms. By contrast, axonal neuropathies associated with MGUS, multiple myeloma, and AL amyloidosis have generally shown no response to therapy. Recently, IgM monoclonal and polyclonal antibodies directed against human peripheral nerve antigens including MAG and various glycolipids such as GM1 ganglioside have been found in patients with specific neuropathy syndromes. Anti-MAG antibodies occur in predominantly sensory demyelinating neuropathies, whereas elevated titers of anti-GM1 ganglioside antibodies are associated with lower motor neuron syndromes with multifocal motor conduction block. Although the evidence for autoimmune mechanisms in some monoclonal protein-associated neuropathies is mounting, a causal connection between monoclonal proteins and these neurologic syndromes has yet to be established.

The association of potentially lethal neurologic syndromes with scleromyxedema (papular mucinosis)

Two patients with scleromyxedema who had progressive neurologic impairment are described. One patient died, and one required prolonged mechanical ventilation. A review of the literature has produced 24 other cases of scleromyxedema in which neurologic changes were prominent.

Extensive demyelinating changes in the peripheral nerves of Crow-Fukase syndrome: a pathological study of one autopsied case

Pathological changes of the peripheral nervous system in one autopsied case of Crow-Fukase syndrome (POEMS syndrome) was systemically examined. Distally accentuated myelinated axon loss was observed in the peripheral nerve trunks, ventral and dorsal spinal roots, but was not observed in the fasciculus gracilis. Segmental demyelination and remyelination associated with focal excessive myelin outfolds were the most characteristic features, the distribution of which was more prominent in the proximal nerve trunks and the spinal nerve roots. Endoneurial edema was present, and focal perivascular T lymphocyte accumulation was occasionally observed in the spinal nerve roots and proximal nerve trunks. Neurons in the sympathetic ganglia, dorsal root ganglia and ventral horns were well preserved.

Acute and remitting painful diabetic polyneuropathy: a comparison of peripheral nerve fibre pathology

The cause of the neuropathic pain that is experienced by some patients with diabetic neuropathy remains to be established. Early neuropathological reports, based on comparisons between diabetic patients and non-diabetic control subjects, emphasised associations between pathological changes in specific classes of peripheral nerve fibre and the presence of pain. By making comparisons with more appropriate control subjects, namely diabetic patients without neuropathic pain, more recent studies have found that there are few clear morphological correlates for this type of pain. To investigate this further, we have conducted a detailed morphometric study of sural nerve biopsies from six diabetic patients, four with active acute painful neuropathy and two with recent remission from the same condition. Normal values for the neuropathological parameters were obtained from six non-diabetic control subjects. Teased fibre analysis showed that similar axonal and Schwann cell abnormalities were present in both groups of diabetic patients. Electron microscopical studies revealed that evidence of both myelinated and unmyelinated fibre degeneration and regeneration was also present in the nerves of all diabetic patients, irrespective of whether they had pain. Within the constraints of interpreting results from small numbers of patients, our observations suggested that remission from pain might be associated with a less abnormal axon/Schwann cell calibre ratio, more successful myelinated fibre regeneration and less active unmyelinated fibre regeneration. However, the inescapable finding of this study was, in fact, the similarity in the nerve fibre pathology in diabetic patients with active and remitting painful neuropathy. We conclude that the occurrence of nerve fibre degeneration and regeneration is in itself unlikely to be sufficient to account fully for diabetic neuropathic pain. However, it is conceivable that events occurring during certain stages in the pathological cycle of degeneration and regeneration create the necessary circumstances which lead to pain.

Peripheral neuropathy in essential mixed cryoglobulinaemia

The prevalence of various forms of peripheral neuropathy has not been previously assessed in large series of patients with essential mixed cryoglobulinaemia (EMC). Clinical and electrophysiological signs of peripheral neuropathy were observed in 21 of 37 EMC patients, consisting of polyneuropathy in 19, mononeuropathy or multiple mononeuropathy in eight, and both in six. The various forms of peripheral neuropathy occurred differently in the subgroups of EMC. Isolated polyneuropathy was more common with type II (eight of 10) than type III EMC (two of eight). Multifocal neuropathy, in association with polyneuropathy, was the most common form in type III EMC (five of eight). Patients with peripheral neuropathy and type II EMC were significantly older than type II EMC patients without neuropathy, regarding present age and age of onset of EMC. Patients with peripheral neuropathy and type III EMC tended to have higher values of ESR and IgM than type III EMC patients without neuropathy. Electrophysiological findings and sural nerve biopsy specimens (nine cases) showed prominent axonal changes. Vascular changes included vasculitis and alterations of the endoneurial microvessels in type II and type III EMC. Our findings suggest that distinct pathogenic factors are implicated in the subgroups of cryoglobulinaemic neuropathy, possibly inducing different types of vascular changes underlying polyneuropathy or, respectively, mononeuropathy and multiple mononeuropathy.

Peripheral neuropathy and multiple myeloma in aging: a case report

A 67-year-old man affected by moderate weight loss, acral paresthesia and plantar burning sensation was admitted to our department. Electromyographic (EMG) and electroneurographic (ENG) studies confirmed a peripheral, asymmetrical, motor-sensorial polyneuropathy (PPN). Hematological data and bone marrow biopsy discovered a non-secerning multiple myeloma (MM). All other probable causes of peripheral neuropathy could be excluded, and the possible relationship between nerve damage and neoplasia was confirmed. Furthermore, all possibilities of association of MM with PPn, namely the osteosclerotic variant, the Crow-Fukase syndrome, and the amyloid one have been evaluated. The only finding of osteolytic bone areas by radiology, the absence of organomegaly, diabetes mellitus, skin alterations, and of amyloid deposition in muscles and nerves, exclude the possible connection of the case to any of the listed possibilities. On the other hand, some clinical aspects differ, in part, to others described in the literature. In conclusion, the association between PPN and MM as the result of multiform clinical variants could be considered.

P.O.E.M.S. syndrome with complete recovery after treatment of a solitary plasmocytoma

The P.O.E.M.S. syndrome is a rare clinical entity that has been described mainly in Japan. It is characterized by a progressive polyneuropathy with raised CSF protein content, organomegaly, endocrinopathy, skin changes and plasma cell dyscrasia. We report a new documented case associated with a solitary plasmocytoma of the 12th thoracic vertebra. Immunopathological and ultrastructural studies of the peripheral nerve did not disclose any immune-specific changes. Surgery and radiation therapy of the plasmocytoma allowed a complete recovery, with a 5-year follow-up. This case report illustrates the need for serial full skeletal survey, including scintigraphy, in middle-aged patients with progressive polyneuropathy of obscure origin.

Axonal atrophy in the painful peripheral neuropathy in AIDS

We compared the sural nerves from patients with AIDS; four with the painful peripheral neuropathy (PPN), three patients with non-painful distal symmetrical peripheral neuropathy (DSPN), one without clinical peripheral nerve involvement and two human immunodeficiency virus negative controls. Fibre diameter distributions showed a slight reduction in larger fibres in all patients with AIDS compared with controls. No significant difference was found in the relative frequency distribution of the lamellae counts between any of the groups. The relative frequency distribution of axonal area of myelinated fibres did not differ between controls, non-painful DSPN or the patient without peripheral nerve involvement; however, all patients with PPN showed marked reduction in the number of axons of myelinated fibres of larger area which was significant when compared to each patient from the other groups (P less than 0.0001). This indicates that the reduction in larger fibres in PPN is mostly due to axonal atrophy rather than selective fibre loss. Axonal atrophy is associated with painful peripheral neuropathy in AIDS but not with those without pain. The possible role of axonal atrophy as a pathological substrate for pain is discussed.

Morphological changes in IgM paraproteinaemic neuropathy

Sural nerve biopsies were examined from two patients with neuropathy associated with IgM kappa [anti-myelin-associated glycoprotein (MAG)] paraproteinaemia. Both nerves had a moderate loss of myelinated fibres. The pathology in one was of a chronic primary demyelinating type, in the other it was associated with axonal atrophy. Widened myelin (WM) was seen in both nerves affecting over 80% and 50% of myelinated fibres, respectively. The WM was associated with deposition of material which sometimes appeared granular but could also display a highly organised pattern, an appearance not previously described in these neuropathies. Granular material was also identified at the external surface of the Schwann cells of myelinated, but not of unmyelinated, fibres. WM was seen not only at the outer lamellae (a commonly observed site) but also at terminal myelin loops at the paranode, at Schmidt Lanterman incisures and at the inner and outer mesaxon. Material was also seen on the inner (adaxonal) Schwann cell surface. These are all sites associated with the presence of MAG. Other pathological features are described, including evidence of impairment of remyelination, abnormal Schwann cell/axon specialisations and the presence of tomaculous bodies. The implications of these findings are discussed.

Rapid quantitative immunohistochemical assessment of human peripheral neuropathies using a monoclonal antibody against nerve growth factor receptor

An analysis of nerve growth factor (NGF) receptor expression and density in human sural nerve biopsies was performed by immunocytochemistry with a murine monoclonal antibody against the human NGF receptor. Quantitative assessment of immunostaining density was made by histospectrophotometry on frozen sections. Although there was enhanced expression of NGF receptor within endoneurium in all patients with clinical neuropathies, expression was highest in nerves with axonal disease, consistent with the proposal that disruption of axon-Schwann cell interactions triggers the re-expression of the NGF receptor. These results with human nerves, together with previous studies with animal models, suggest that NGF and NGF receptor play important roles in the general response to neuronal injury.

Pathological findings in three non-Japanese patients with the POEMS syndrome

The pathological features of three European patients with plasma cell dyscrasia, osteosclerosis and a multisystem disorder, most frequent in Japan, that includes polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes (POEMS syndrome), are reported. The material was obtained from biopsies (peroneal nerve, lymph node) and general autopsy, including hypophysis, in one case. The most salient findings were: peripheral nerve lesions, including both segmental demyelination and axonal degeneration, with so-called uncompacted myelin lamellae (UML); angiofollicular lymph node hyperplasia (AFLNH); and non inflammatory vascular changes. Though not specific, it appears that UML and AFLNH may be contributive findings in atypical cases of POEMS syndrome (incomplete forms, lack of underlying malignant plasma cell dyscrasia or circulating monoclonal immunoglobulin). Among the various autopsy findings we emphasize the skin thickening which was secondary to a hyaline sclerosis of the papillary dermis, and the presence in adenohypophysis of numerous cells showing positive reactions with the anti-alpha MSH antibody. Though immunological, vascular and hormonal disturbances have been implicated at the origin of several manifestations of the disorder, the pathogenesis of the POEMS syndrome remains obscure.

Susceptibility to pressure neuropathy distal to a constricting ligature in the guinea-pig

Silk ligatures were tied round the sciatic nerve in guinea-pigs and left in place in order to produce persistent nerve constriction. Serial nerve conduction studies over the following 9 weeks showed a reduction in motor conduction velocity distal to the ligature. The presence of axonal atrophy in tibial nerve fibres in the leg was subsequently confirmed by histological studies. These changes were not seen in a second group of animals in which similar ligatures were tied but removed after 6 hours. When the ligatures were left in place, the animals developed local plantar nerve lesions in the sole of the foot on the affected side, which were thought to be due to pressure from the floor of the cage. Local pressure changes of varying severity were seen in the foot in all the constricted nerves, but were only occasionally found in control nerves from the opposite foot, or in nerves which had been constricted for a few hours by ligatures which were then removed. These results suggest that atrophic nerve fibres distal to a persistent constriction may be particularly sensitive to local pressure.

Adaptation of the myelin sheath during axonal atrophy

Distal axonal atrophy was produced by proximal constriction of the tibial nerve in the rabbit. Single fibres were teased from the distal tibial nerve, and a selected internode from each fibre was measured and then cut transversely for electron microscopy, so that axon area and perimeter, myelin lamellar number and periodicity, and myelin spiral length could be related to the length of the internode which had been sectioned. When sections from atrophic and control internodes of similar length were compared, there was no difference in the mean number of myelin lamellae or their periodicity in the two groups, in spite of a mean reduction in axon cross-sectional area of 60% in the atrophic group. Mean values for axon perimeter and myelin spiral length were reduced by 14%-15% in atrophic fibres, compared with controls. The reduction in mean myelin spiral length might seem to imply that myelin had been lost from the atrophic internodes. However, there was also an increase in the length of individual lamellae in the long axis of the internode, due to the irregular folding of the sheath, and it is uncertain whether any overall change in internodal myelin volume had occurred.

Relation between myelin sheath thickness, internode geometry, and sheath resistance

The thickness of the myelin sheath of nerve fibers was traditionally assessed solely as a function of axon caliber. Studies concerning the additional effect of variation in internode length are of relatively recent date. Carefully calibrated measurements of sheath thickness and internode geometry were used in this study to define an equation to predict the approximate number of lamellae from axon caliber and internode length, for normal and regenerated peripheral nerve fibers, and for fibers from hypomyelinated murine mutants. The definition of sheath thickness thus obtained was compared with different assumptions on the biophysical nature of myelin sheath resistance. The observed relations between sheath thickness and internode geometry were not compatible with an effective adjustment of sheath thickness to a radial flow of current across the sheath. Conversely, sheath thickness was found to vary in such a way that the resistance of the spiral path between the lamellae was matched precisely to axonal current density. The calculated resistance of the spiral leakage path, furthermore, was equal to measured sheath resistance. This new concept reconciles low sheath resistance with a high resistance of the myelin leaflet, yielding, at the same time, a fine tuning of sheath resistance to variations of internode geometry.