Peripheral nerve damage during multiple myeloma and Waldenstrom's macroglobulinemia: an ultrastructural and immunopathologic study

Amyloid-like IgM deposition neuropathy with multiple mononeuropathies and generalized neuropathy

Amyloid-like IgM deposition neuropathy is a distinct entity in the setting of IgM monoclonal gammopathy in which endoneurial perivascular entire IgM-particle accumulation leads to a painful sensory followed by motor peripheral neuropathy. We report a 77-year-old man presenting with progressive multiple mononeuropathies starting with painless right foot drop. Electrodiagnostic studies showed severe axonal sensory-motor neuropathy superimposed by multiple mononeuropathies. Laboratory investigations were remarkable for biclonal gammopathy of IgM kappa, IgA lambda and severe sudomotor and mild cardiovagal autonomic dysfunction. A right sural nerve biopsy showed multifocal axonal neuropathy, prominent microvasculitis, and prominent large endoneurial deposits of Congo-red negative amorphous material. Laser dissected mass spectrometry-based proteomics identified IgM kappa deposit without serum amyloid-P protein. This case has several distinctive features, including motor preceding sensory involvement, prominent IgM-kappa proteinaceous deposits replacing most of the endoneurium, a prominent inflammatory component, and improvement of motor strength after immunotherapy.

Paraproteinemia and neuropathy

Paraproteinemia is associated with different peripheral neuropathies. The major causes of neuropathy correlated with paraproteinemia are the deposition of immunoglobulin in the myelin, represented by anti-myelin-associated glycoprotein (MAG) neuropathy; deposition of immunoglobulin or its fragment in the interstitium, represented by immunoglobulin light chain amyloidosis (AL amyloidosis); and paraneoplastic mechanisms that cannot be solely attributed to the deposition of immunoglobulin or its fragment, represented by polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin change (POEMS) syndrome. Patients with anti-MAG neuropathy and POEMS syndrome present with slowing of nerve conduction parameters. This characteristic fulfills the electrodiagnostic criteria for chronic inflammatory demyelinating polyneuropathy (CIDP) defined by the European Academy of Neurology and Peripheral Nerve Society (EAN/PNS). Although direct damage caused by the deposition of amyloid can induce axonal damage in AL amyloidosis, some patients with this condition have features fulfilling the EAN/PNS electrodiagnostic criteria for CIDP. Conventional immunotherapies for CIDP, such as steroids, intravenous immunoglobulin, and plasma exchange, offer no or only minimal-to-modest benefit. Although rituximab can reduce the level of circulating autoantibodies, it may only be effective in some patients with anti-MAG neuropathy. Drugs including melphalan, thalidomide, lenalidomide, and bortezomib for POEMS syndrome and those including melphalan, thalidomide, lenalidomide, pomalidomide, bortezomib, ixazomib, and daratumumab for AL amyloidosis are considered. Since there will be more therapeutic options in the future, thereby enabling appropriate treatments for individual neuropathies, there is an increasing need for early diagnosis.

Significance of Oligomeric and Fibrillar Species in Amyloidosis: Insights into Pathophysiology and Treatment

Amyloidosis is a term referring to a group of various protein-misfolding diseases wherein normally soluble proteins form aggregates as insoluble amyloid fibrils. How, or whether, amyloid fibrils contribute to tissue damage in amyloidosis has been the topic of debate. In vitro studies have demonstrated the appearance of small globular oligomeric species during the incubation of amyloid beta peptide (Aβ). Nerve biopsy specimens from patients with systemic amyloidosis have suggested that globular structures similar to Aβ oligomers were generated from amorphous electron-dense materials and later developed into mature amyloid fibrils. Schwann cells adjacent to amyloid fibrils become atrophic and degenerative, suggesting that the direct tissue damage induced by amyloid fibrils plays an important role in systemic amyloidosis. In contrast, there is increasing evidence that oligomers, rather than amyloid fibrils, are responsible for cell death in neurodegenerative diseases, particularly Alzheimer’s disease. Disease-modifying therapies based on the pathophysiology of amyloidosis have now become available. Aducanumab, a human monoclonal antibody against the aggregated form of Aβ, was recently approved for Alzheimer’s disease, and other monoclonal antibodies, including gantenerumab, solanezumab, and lecanemab, could also be up for approval. As many other agents for amyloidosis will be developed in the future, studies to develop sensitive clinical scales for identifying improvement and markers that can act as surrogates for clinical scales should be conducted.

The Ultrastructure of Tissue Damage by Amyloid Fibrils

Amyloidosis is a group of diseases that includes Alzheimer’s disease, prion diseases, transthyretin (ATTR) amyloidosis, and immunoglobulin light chain (AL) amyloidosis. The mechanism of organ dysfunction resulting from amyloidosis has been a topic of debate. This review focuses on the ultrastructure of tissue damage resulting from amyloid deposition and therapeutic insights based on the pathophysiology of amyloidosis. Studies of nerve biopsy or cardiac autopsy specimens from patients with ATTR and AL amyloidoses show atrophy of cells near amyloid fibril aggregates. In addition to the stress or toxicity attributable to amyloid fibrils themselves, the toxicity of non-fibrillar states of amyloidogenic proteins, particularly oligomers, may also participate in the mechanisms of tissue damage. The obscuration of the basement and cytoplasmic membranes of cells near amyloid fibrils attributable to an affinity of components constituting these membranes to those of amyloid fibrils may also play an important role in tissue damage. Possible major therapeutic strategies based on pathophysiology of amyloidosis consist of the following: (1) reducing or preventing the production of causative proteins; (2) preventing the causative proteins from participating in the process of amyloid fibril formation; and/or (3) eliminating already-deposited amyloid fibrils. As the development of novel disease-modifying therapies such as short interfering RNA, antisense oligonucleotide, and monoclonal antibodies is remarkable, early diagnosis and appropriate selection of treatment is becoming more and more important for patients with amyloidosis.

Two distinct mechanisms of neuropathy in immunoglobulin light chain (AL) amyloidosis

INTRODUCTION

Although polyneuropathy in patients with immunoglobulin light chain (AL) amyloidosis has been considered to be attributable to axonal degeneration resulting from amyloid deposition, patients with nerve conduction parameters indicating demyelination that mimics chronic inflammatory demyelinating polyneuropathy (CIDP) have also been reported anecdotally.

METHODS

We evaluated the electrophysiological and pathological features of 8 consecutive patients with AL amyloidosis who were referred for sural nerve biopsy.

RESULTS

Although findings of axonal neuropathy predominantly in the lower limbs were the cardinal feature, all patients showed one or more abnormalities of nerve conduction velocities or distal motor latencies. In particular, 2 of these patients fulfilled the definite electrophysiological for CIDP defined by the European Federation of Neurological Societies/Peripheral Nerve Society (EFNS/PNS). On electron microscopic examination of sural nerve biopsy specimens, Schwann cells apposed to amyloid fibrils became atrophic in all patients, suggesting that amyloid deposits directly affect neighboring tissues. Additionally, detachment of the neurilemma from the outermost compacted myelin lamella was seen where amyloid fibrils were absent in 4 patients. Electrophysiological findings suggestive of demyelination were more conspicuous in these patients compared with the other patients. The detachment of the neurilemma from the outermost compacted myelin lamella was particularly conspicuous in patients who fulfilled the definite EFNS/PNS electrophysiological criteria for CIDP.

CONCLUSION

Abnormalities of myelinated fibers unrelated to amyloid deposition may frequently occur in AL amyloidosis. Disjunction between myelin and the neurilemma may induce nerve conduction abnormalities suggestive of demyelination.

Waldenström's Macroglobulinemia Associated With Generalized AA-Amyloidosis

The authors present a case of Waldenström's macroglobulinemia (WM) associated with generalized amyloidosis of amyloid-A type. A 77-year-old man with a 25-year history of degenerative joint disease and a 13-year history of WM died of multisystemic failure. At autopsy, generalized and severe amyloid deposits were detected. Special conventional stains and immunohistochemical examination revealed amyloid-A de posits, which are extinguishingly rare in WM. This is probably related to the disease being chronic, which results in excessive production of precursor protein. The detection of amyloid-A type fibrils was possible only through the application of the immunohis tochemical procedure. The authors emphasize using the immunohistochemical typing of amyloid deposits for the purpose of classification, therapy, and prognosis. Int J Surg Pathol 1 (2):123-128, 1993

Amyloid-like IgM deposition neuropathy: a distinct clinico-pathologic and proteomic profiled disorder

Some patients with immunoglobulin paraproteinemic neuropathy have intra-nerve deposits that morphologically mimick amyloid, but do no stain with Congo red. Patients with amyloid-like deposits were identified. The nerve amyloid-like aggregates were studied by laser microdissection and dual mass spectrometry. Three male patients, all with IgM gammopathy, and neuropathy were identified. Follow-up, disease duration was 5, 19, and 7 years, respectively. All had progressive asymmetric sensory-onset distal axonal polyneuropathy with late motor involvement. Autonomic symptoms occurred in only one after 13 years of symptoms. None had clinical cardio-renal involvement. One had skin papules with dermal amyloid-like deposits. Endoneurial amyloid-like deposits had granulo-fibrillar ultrastructure. Mass spectrometry of laser-dissected deposits identified IgM pentameric macroglobulin (heavy, light, and joining chains) without amyloid-associated proteins including absent apolipoprotein E and serum amyloid P-component. Amyloid-like neuropathy has distinct clinical, pathologic, and proteomic features which expand the spectrum of IgM neuropathies. Patients have favorable survival, relative absence of autonomic features, and distinct proteomic profiles of the infiltrative protein in nerve.

Heterogeneous spectrum of neuropathies in Waldenström's macroglobulinemia: a diagnostic strategy to optimize their management

Neuropathy in Waldenström's macroglobulinemia (WM) is very heterogeneous. We retrospectively studied 40 patients with WM and neuropathy to analyze the different presentations and mechanisms encountered and to propose a diagnostic strategy. Twenty-five patients (62.5%) had axonal neuropathy, related to the following mechanisms: amyloid neuropathy (n = 5), cryoglobulinemic neuropathy (n = 5), neuropathy associated with tumoral infiltration (n = 2), vasculitic neuropathy (n = 2), a clinical motor neuropathy possibly of dysimmune origin (n = 6), or an unclassified mechanism (n = 5). A demyelinating pattern was observed in 15 patients, 10 having anti-myelin-associated glycoprotein (anti-MAG) antibodies and 5 having neuropathy related to chronic inflammatory demyelinating polyradiculoneuropathy. On the basis of these results, we propose a diagnostic strategy combining: (1) an EMG to distinguish between a demyelinating and an axonal pattern; (2) measurement of anti-MAG and anti-ganglioside antibodies; (3) screening for "red flag" features to orientate further investigations. This strategy may help clinicians to identify the mechanism of neuropathy in order to adapt the therapeutic strategy.

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.

Peripheral nervous system involvement in patients with cancer

Involvement of the peripheral nervous system (PNS) is common in patients with cancer and any part, including motor neurons, sensory ganglia, nerve roots, plexuses, cranial and peripheral nerves, and neuromuscular junctions, can be affected. Different mechanisms can initiate damage associated with cancer-related PNS disorders. These include tumour infiltration, toxicity of treatments, metabolic and nutritional perturbations, cachexia, virus infections, and paraneoplastic neurological syndromes. The type of cancer, lymphoma, or solid tumour is a further determinant of a PNS disorder. In this Review we discuss the different causes and mechanisms of disorders of the PNS in patients with cancer and we will focus on their assessment and diagnosis.

Paraneoplastic neurologic syndromes

Cancer can affect the nervous system through many metastatic and nonmetastatic mechanisms, including side effects of cancer treatment, infections, coagulopathy, and metabolic or nutritional deficits. Paraneoplastic neurologic disorders (PND) are an extensive group of syndromes that cannot be explained by any of these complications and may affect any part of the nervous system. PND often develop before the presence of a cancer is known and their recognition may lead to the tumor diagnosis.

Paraneoplastic syndromes of the spinal cord, nerve, and muscle

Cancer can affect the peripheral nervous system by non-metastatic, sometimes immune-mediated mechanisms. Recognition of these paraneoplastic syndromes is important because it can lead to the detection of the tumor, and also helps to avoid unnecessary studies to determine the cause of the neurologic symptoms in patients with cancer. Many paraneoplastic syndromes of the peripheral nervous system are not associated with serum antibodies that serve as markers of paraneoplasia. For this group of disorders the diagnosis depends on the clinician's index of suspicion and conventional electrophysiologic and laboratory tests. Treatment of the tumor, immunotherapy, or both may improve some of these syndromes. This review focuses on paraneoplastic syndromes of the spinal cord, peripheral nerve, and muscle.

Cardiac paraprotein associated with Waldenstrom's macroglobulinemia: a case report

A case of myocardial paraprotein deposition in a patient with Waldenstrom's macroglobulinemia is presented. Routine light microscopy revealed diffuse widening of interstitial regions by pale eosinophilic material that had a grayish cast on trichrome stains and was Congo red negative. Immunofluorescence showed strong immunoglobulin M and kappa light chain staining around blood vessels but predominantly around myocytes. Ultrastructural examination revealed massive deposition of flocculent electron-dense material around myocytes and occasionally around blood vessels.

Mental nerve neuropathy: a symptom of Waldenström's macroglobulinemia

The uncontrolled production of immunoglobulins in Waldenström's macroglobulinemia, a neoplastic plasma cell disorder, results in hyperviscosity of blood and multisystem organ derangement. Previously reported orofacial manifestations have been limited to osteolytic lesions of the jaw, ulcerations of the mucosa and tongue, gingival bleeding, and enlargement of salivary and lacrimal glands. Mental nerve anesthesia resulting from IgM deposition on the myelin sheath is a previously unreported early warning sign of advancing disease. Its occurrence heralds the need for aggressive medical management.

Pathology of dysproteinemia: light chain amyloidosis, non-amyloid immunoglobulin deposition disease, cryoglobulinemia syndromes, and macroglobulinemia of Waldenström

This review has dealt with four syndromes associated with dysproteinemia, and has emphasized studies of the tissue deposits and forms of tissue injury which occur in such patients. However, similar tissue deposits and tissue damage occasionally occur in the absence of a serum or urine paraprotein, in which case other clinical data are necessary to suggest the need for examination of tissue for Ig heavy and light chain determinants in order to provide a correct diagnosis of dysproteinemia. In such cases, one may speculate that there is a low rate of paraprotein production and secretion, in addition to tissue tropism. Some paraproteins are antibodies, in which case they may circulate and/or deposit as immune complexes, or bind to tissue antigens with immune complex formation in situ. Some paraproteins are also cryoproteins, and clues to this property can also be found in the tissue, particularly at the ultrastructural level. Thus, a wide spectrum of clinical manifestations of a B cell proliferative disorder may be associated with any of a variety of circulating paraproteins and a variety of forms of tissue deposit and injury. Consequently, the best understanding of an individual patient requires correlation of the clinical features of the disorder, the immunochemical characterization of the circulating and excreted paraproteins, and an immunohistochemical analysis of the tissue deposits and associated morphologic abnormalities. This should be correlated with histologic and immunohistologic assessment of bone marrow, looking for overt B cell neoplasia, the more difficult to define "lymphoproliferative disorders," or alterations in kappa to lambda plasma cell ratios which may correlate with the deposited material. Studies of the Ig synthesized by cultured bone marrow plasma cells, and biochemical analyses of the deposited material, have demonstrated structural abnormalities of paraproteins which may be responsible for their tissue deposition.

Association of Guillain-Barré syndrome and Henoch-Schönlein purpura: is immunoglobulin a responsible for the neurologic syndrome?

Guillain-Barré syndrome and Henoch-Schönlein purpura (HSP) appeared simultaneously in a 35-year-old woman. During the course of the Guillain-Barré syndrome, the presence of IgA aggregates and a decrease in complement components were noted in the cerebrospinal fluid. These abnormalities disappeared when the neurologic syndrome remitted. This suggests the responsibility of IgA immune complexes, characteristic of HSP, in the occurrence of the associated Guillain-Barré syndrome.

Altered blood rheology in the pathogenesis of diabetic and other neuropathies

Although a substantial literature confirms the abnormal flow properties of diabetic blood, only in a few papers has the vasculitis of diabetic neuropathy been considered to have a hemorheological cause. It is proposed that the pathogenesis of nerve lesions involves an interaction between the specialized nerve vascular system and focal ischemic lesions resulting from rheologically induced stasis. The proposition is extended into other conditions with abnormal blood rheology such as hypothyroidism, uremia, dysglobulinemia, polyarteritis nodosa, and lepromatous leprosy. It is concluded that the treatment of such polyneuropathies should include an agent which would improve the flow properties of the blood.

Plasma cell dyscrasias: current status

This is a review of the current status of the monoclonal gammopathies (plasma cell dyscrasias). We begin with the recognition of a monoclonal protein in serum and urine. We briefly discuss the differential diagnosis of the monoclonal gammopathies. Clinical and laboratory findings as well as the management of multiple myeloma are addressed. Future approaches for the treatment of myeloma are provided. The variant forms of multiple myeloma, including smoldering myeloma, plasma cell leukemia, nonsecretory myeloma, IgD myeloma, osteosclerotic myeloma, solitary plasmacytoma of bone, and extramedullary plasmacytoma, are briefly reviewed. Diagnosis and treatment of Waldenström's macroglobulinemia are presented. The recognition and differential diagnosis of the heavy-chain diseases (gamma, alpha, and mu) are included. Monoclonal gammopathy of undetermined significance ("benign" monoclonal gammopathy) is presented in detail. Amyloidosis is not included in this review.

Mononeuritis multiplex in Waldenström's macroglobulinemia

We describe a patient with mononeuritis multiplex who had cranial nerve involvement in association with Waldenström's macroglobulinemia. Sural nerve biopsy showed abundant endoneurial granulofibrillary deposits related to microangiopathic changes. These changes were distributed in a multifocal pattern among the fascicles. Immunohistochemistry demonstrated the IgM nature of the deposit located in the endoneurial interstitium.

Successful treatment of peripheral neuropathy with chemotherapy in osteosclerotic myeloma

A patient with a severe polyneuropathy in association with osteosclerotic myeloma improved after melphalan and prednisone treatment. Aggressive treatment with chemotherapy is appropriate in this type of patient.

Immunofluorescence study of patients with neuropathy and IgM M proteins

Immunofluorescence histochemistry was used to study the pathogenesis of polyneuropathy in patients with an IgM M protein. Seventeen patients had an M protein that reacted with myelin-associated glycoprotein (MAG), and their serum immunostained myelin sheaths of normal peripheral nerve of humans and certain other species. The staining was specific for the M protein idiotype and was abolished by prior absorption of serum with MAG. The sural nerve biopsy specimens from these 17 patients had pathological features of primary demyelination and deposits of IgM on the myelin sheaths. Sural nerve specimens of 2 patients with an M protein reactive with chondroitin sulfate showed axonal degeneration and diffuse deposits of IgM in the endoneurium. Serum of one of these patients immunostained connective tissue; the staining was specific for the M protein idiotype and was blocked by absorption of the serum with chondroitin sulfate. The antigenic specificity of the IgM M protein in another 9 patients with neuropathy is not known; however, sural nerve specimens obtained from some of the patients showed axonal degeneration and endoneurial deposits of IgM, and the serum IgM immunostained axons in some instances. The findings suggest that IgM M proteins may cause the neuropathy and that more than one autoantigen is involved.

Polyneuropathy in paraproteinaemia

Paraproteinaemias are frequently associated with peripheral neuropathies. "Benign" paraproteinaemia, myeloma and Waldenströms macroglobulinaemia may present clinically as polyneuropathy. Therefore immunoelectrophoresis is strongly recommended in the routine diagnosis of polyneuropathies of unknown origin. Peripheral neuropathies associated with paraproteinaemia are clinically, electrophysiologically, pathologically and probably also pathogenetically heterogeneous. There are subgroups such as demyelinating neuropathy associated with IgM paraproteinaemia, which show quite distinctive features. This survey describes the different types of paraproteinaemia and their associated peripheral neuropathies. The incidence, pathogenesis and therapy of peripheral neuropathy associated with monoclonal gammopathies are discussed.

Axonal attenuation and secondary segmental demyelination in myeloma neuropathies

The sural nerves of 5 patients with osteosclerotic myeloma and polyneuropathy, of 3 patients with multiple myeloma and polyneuropathy, and of 6 healthy subjects were studied by neuropathological, morphometric, and teased-fiber approaches to assess cellular (Schwann cell or axon) vulnerability and to explore the mechanism of segmental demyelination. As compared with controls, the nerves of both types of myeloma neuropathy demonstrated a statistically significant and marked loss of myelinated fibers and increased frequencies of axonal degeneration among teased fibers at statistically significant levels. The peaks of diameter histograms of myelinated fibers of osteosclerotic myeloma/polyneuropathy nerves were displaced to smaller diameter categories, suggesting fiber atrophy. Segmental demyelination and remyelination was clustered, as found in secondary demyelination. Large- and intermediate-diameter myelinated fibers of osteosclerotic myeloma/polyneuropathy nerves had significantly smaller axon calibers relative to myelin spiral length seen in electron micrographs. The loss of myelinated fiber axons, the shift of the peaks of diameter histograms to smaller sizes, the lack of noticeable increased numbers of demyelinated axons, the clustered distribution of segmental demyelination, and the axonal attenuation suggest a special axonal or neuronal vulnerability and appear to provide an explanation for the observed segmental demyelination. Whether axonal attenuation has a perikaryeal or proximal axonal genesis now needs to be determined.

Peripheral neuropathies associated with monoclonal proteins: a clinical review

Over the last decade, the increasing use of serum and urine protein electrophoretic screening of patients with idiopathic peripheral neuropathy has led to greater recognition of peripheral neuropathy syndromes that are associated with monoclonal proteins and plasma cell dycrasias. After careful evaluation, most of these patients have benign monoclonal gammopathy, followed in frequency by primary systemic amyloidosis and osteosclerotic myeloma, with occasional cases associated with osteolytic multiple myeloma, Waldenstrom's macroglobulinemia, gamma heavy chain disease, and other rare disorders. Several of these syndromes have distinctive presentations and are recognizable clinically, whereas others (especially multiple myeloma neuropathy) are diverse clinically and are not clearly distinguishable from other chronic neuropathies. The discovery of IgM-kappa monoclonal proteins directed at myelin antigens in some patients with benign monoclonal gammopathy and the delineation of the syndrome of neuropathy and multiorgan involvement in osteosclerotic myeloma are important developments which may shed light on the mechanism of the remote effects of malignancies on the nervous system.

IgM demyelinative neuropathy with amyloidosis and biclonal gammopathy

A 59-year-old man developed a sensorimotor neuropathy of the upper and lower limbs, associated with a biclonal gammopathy, within the space of a few months. Each of two paraproteins was coupled with a distinct IgM kappa IgG lambda light chain. Examination of a nerve biopsy specimen by electron microscopy revealed a demyelinative process with a widening of the interlaminar space in the myelin sheath, as well as deposits of amyloid substance between nerve fibers. Direct immunofluorescence revealed the presence of IgM and of the kappa light chain in certain Schwann cells, while the lambda IgG was fixed to the amyloid deposits. Immunoperoxidase histochemistry showed a positive reaction in normal human nerve tissue to the immune serum IgM and kappa light chain. The findings suggest that the widening of the interlaminar space of the diseased myelin corresponds to an active fixation of immunoglobulin on the sheath of the Schwann cell. The presence of two light chains in this patient's gammopathy caused a dual pathology: the kappa chain, a demyelinative neuropathy, and the lambda chain, a primary amyloidosis, with deposits in the peripheral nerve and in the kidney.

Microangiopathy of vasa nervorum in dysglobulinemic neuropathy

Thickening of vessel walls resulting from endothelial proliferation was observed in the vasa nervorum of eleven patients with peripheral neuropathy associated with dysglobulinemia. Electron microscopy showed endothelial proliferation accompanied by abnormal accumulation of masses of intracytoplasmic filaments in each case. Of the eleven patients with dysglobulinemia, nine had monoclonal gammopathy and two were found to have polyclonal elevation of gamma globulin levels. Symptoms of neuropathy characteristically preceded detection of serum protein abnormalities by months to years. Nerve fiber lesions involved primarily the axon in four cases; segmental demyelination was the principal abnormality in the other seven. Both abnormalities were present to some degree in all eleven patients. Biphasic myelinopathy with uniform separation of myelin lamellae attributable to globulin deposition was observed in four cases. The microvascular changes included endothelial cytoplasmic enlargement, virtually obliterating the vessel lumen in many instances, with thickening of pericytes, in which intracytoplasmic filaments were prominent and pinocytotic vesicles numerous. No extracellular filaments were noted, and amyloid stains were negative. Possible effects of these microvascular changes include ischemia resulting from severe vascular luminal narrowing, and altered vascular permeability. Severe loss of axons in this group of neuropathies may be the result of ischemia, whereas altered vascular permeability may admit globulin into the endoneurium, where it may directly affect the myelin sheath and precipitate demyelination.

Uncompacted myelin lamellae in two cases of peripheral neuropathy

Peripheral nerve biopsies from two patients with chronic sensorimotor neuropathy were studied. The first case was a non-Hodgkin malignant lymphoma and did not show any dysglobulinemia. The second case had a benign monoclonal gammopathy IgG, Lambda type. Direct immunofluorescence showed no deposits in the first case and slight deposits of anti IgG sera on a few myelinated fibers in the second case. There were numerous fibers showing uncompacted myelin lamellae, 7% in the first case and 4% in the second case. Some of these fibers had axons containing more tubules than filaments. The very few cases reported on neuropathies showing that uncompacted myelin lamellae were frequently associated with dysglobulinemic neuropathy. However, this ultrastructural abnormality of the myelin sheath can be observed without any dysglobulinemia.