Immunofixation superior to plasma agarose electrophoresis in detecting small M-components in patients with polyneuropathy

Paraproteinemic Neuropathies

OBJECTIVE

Coexistence of polyneuropathy and gammopathy is a common but potentially challenging situation in clinical practice. This article reviews the clinical, electrophysiologic, and hematologic phenotypes of the paraproteinemic neuropathies and the diagnostic and treatment strategies for each.

LATEST DEVELOPMENTS

Advances in our understanding of the underlying pathophysiology of various paraproteinemic neuropathies and their corresponding phenotypes have identified potential new therapeutic targets. Therapeutic strategies to diminish anti-myelin-associated glycoprotein (MAG) IgM antibodies have shown partial and inconsistent efficacy; however, antigen-specific immune therapy is being investigated as a novel treatment to remove the presumably pathogenic anti-MAG antibody. Advances in genetic and cell signaling studies have resulted in the approval of Bruton tyrosine kinase inhibitors for Waldenström macroglobulinemia. Monoclonal antibodies are being investigated for the treatment of light chain amyloidosis.

ESSENTIAL POINTS

Early recognition and treatment of underlying plasma cell disorders improves clinical outcomes in patients with paraproteinemic neuropathy. Despite significant progress, our knowledge regarding underlying mechanisms for paraproteinemic neuropathy is still limited. Clinicians' awareness of clinical phenotypes, electrophysiologic hallmarks, and hematologic findings of the different paraproteinemic neuropathies is crucial to promptly identify and treat patients and to avert misdiagnosis. Multidisciplinary collaboration among specialists, including neurologists and hematologists, is paramount for the optimal treatment of these patients with overlapping conditions.

Antibody testing in neuropathy associated with anti-Myelin-Associated Glycoprotein antibodies: where we are after 40 years

PURPOSE OF REVIEW

The diagnosis of Myelin-Associated Glycoprotein (MAG) neuropathy is based on the presence of elevated titers of IgM anti-MAG antibodies, which are typically associated with IgM monoclonal gammopathy, and a slowly progressive, distal demyelinating phenotype. The condition, however, can be under or over diagnosed in patients with mildly elevated antibody titers, absent monoclonal gammopathy, or an atypical presentation. The purpose of this paper is to examine recent advances in our understanding of the currently available anti-MAG antibody assays, their reliability, and their use in deciding treatment or monitoring the response to therapy.

RECENT FINDINGS

Higher titers of anti-MAG antibodies are more likely to be associated with the typical MAG phenotype or response to therapy. Mildly elevated antibody levels can occur in patients with chronic inflammatory demyelinating polyneuropathy. Testing for cross-reactivity with HNK1 can add to the specificity of the antibody assays. Patients with MAG neuropathy can present with an atypical phenotype and in the absence of a detectable monoclonal gammopathy.

SUMMARY

Assays for anti-MAG antibodies by Enzyme-Linked Immunosorbent Assay can be improved by testing for antibody binding at multiple serum dilutions, the inclusion of antigen-negative microwells as internal controls for each sample, testing for cross-reactivity with HNK1, and formal validation. The diagnosis needs to be considered in patients with demyelinating neuropathy, even in the absence of a monoclonal gammopathy or typical phenotype. The change in antibody levels needs to be considered in evaluating the response to therapy with B-cell depleting agents.

Acute Autonomic Symptoms with Anti-myelin-associated Glycoprotein Neuropathy as a Presentation of Small B Cell Lymphoma: A Case Report and Literature Review

The association of symmetrical distal sensorimotor polyneuropathy with anti-myelin-associated glycoprotein antibodies (MAG) has been well established. Although autonomic symptoms are uncommon with anti-MAG antibody neuropathy (MAN). We are presenting an unusual case, who developed acute onset urinary retention, orthostatic hypotension, bradycardia and was found to have MAN. She was a 68-year-old lady, presented with progressive ascending numbness, weakness of her extremities and balance problems. On neurological examination, she had generalized muscle weakness, reduced perception to all modalities of sensation with marked impairment of vibration and position sense in the lower limbs. Reflexes were diminished throughout and Romberg sign was positive. Initial lab work including thyroid-stimulating hormone (TSH), vitamin B12, Hb1c, and routine lab reports was normal. The patient then developed acute urinary retention, severe orthostatic hypotension, and symptomatic bradycardia. Workup during this time revealed M spike on serum electrophoresis with IgM kappa on immunofixation. IgM titers were higher than normal. Initially, she was thought to have monoclonal gammopathy of undetermined significance (MGUS) related neuropathy but further workup showed very high levels of anti-MAG antibody titer. Further workup including a bone marrow biopsy revealed a small B cell lymphoma. Only a few cases have reported a small B cell lymphoma presenting with MAN-associated autonomic symptoms. She is currently being treated with rituximab with significant improvement in her neuropathic symptoms. Further case studies are needed to show whether autonomic symptoms are the feature of MAN or this atypical presentation is the paraneoplastic manifestation of the lymphoma.

Diagnosis and treatment of chronic acquired demyelinating polyneuropathies

Chronic neuropathies are operationally classified as primarily demyelinating or axonal, on the basis of electrodiagnostic or pathological criteria. Demyelinating neuropathies are further classified as hereditary or acquired-this distinction is important, because the acquired neuropathies are immune-mediated and, thus, amenable to treatment. The acquired chronic demyelinating neuropathies include chronic inflammatory demyelinating polyneuropathy (CIDP), neuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG; anti-MAG neuropathy), multifocal motor neuropathy (MMN), and POEMS syndrome. They have characteristic--though overlapping--clinical presentations, are mediated by distinct immune mechanisms, and respond to different therapies. CIDP is the default diagnosis if the neuropathy is demyelinating and no other cause is found. Anti-MAG neuropathy is diagnosed on the basis of the presence of anti-MAG antibodies, MMN is characterized by multifocal weakness and motor conduction blocks, and POEMS syndrome is associated with IgG or IgA λ-type monoclonal gammopathy and osteosclerotic myeloma. The correct diagnosis, however, can be difficult to make in patients with atypical or overlapping presentations, or nondefinitive laboratory studies. First-line treatments include intravenous immunoglobulin (IVIg), corticosteroids or plasmapheresis for CIDP; IVIg for MMN; rituximab for anti-MAG neuropathy; and irradiation or chemotherapy for POEMS syndrome. A correct diagnosis is required for choosing the appropriate treatment, with the aim of preventing progressive neuropathy.

Neuropathy and monoclonal gammopathy

The association of neuropathy with monoclonal gammopathy has been known for several years, even if the clinical and pathogenetic relevance of this association is not completely defined. This is not a marginal problem since monoclonal gammopathy is present in 1-3% of the population above 50 years in whom it is often asymptomatic, and in at least 8% of patients is associated with a symptomatic neuropathy, representing one of the leading causes of neuropathy in aged people. Monoclonal gammopathy may result from malignant lymphoproliferative diseases including multiple myeloma or solitary plasmocytoma, Waldenström's macroglobulinemia (WM), other IgM-secreting lymphoma or chronic lymphocytic leukemia, and primary systemic amyloidosis (AL). In most instances it is not associated with any of these disorders and is defined monoclonal gammopathy of undetermined significance (MGUS) for its possible, though infrequent, evolution into malignant forms. Several data support the pathogenetic role of the monoclonal gammopathy in the neuropathy particularly when of IgM isotype where IgM reactivity to several neural antigens has been reported. Increased levels of VEGF have been implicated in POEMS syndrome. However, there are as yet no defined therapies for these neuropathies, as their efficacy has not been confirmed in randomized trials.

European Federation of Neurological Societies/Peripheral Nerve Society guideline on management of paraproteinaemic demyelinating neuropathies: report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society*

BACKGROUND

Paraprotein-associated neuropathies have heterogeneous clinical, neurophysiological, neuropathological and haematological features. Objectives. To prepare evidence-based and consensus guidelines on the clinical management of patients with both a demyelinating neuropathy and a paraprotein (paraproteinaemic demyelinating neuropathy, PDN).

METHODS

Search of MEDLINE and the Cochrane library, review of evidence and consensus agreement of an expert panel.

RECOMMENDATIONS

In the absence of adequate data, evidence based recommendations were not possible but the panel agreed the following good practice points: (1) Patients with PDN should be investigated for a malignant plasma cell dyscrasia. (2) The paraprotein is more likely to be causing the neuropathy if the paraprotein is immunoglobulin (Ig)M, antibodies are present in serum or on biopsy, or the clinical phenotype is chronic distal sensory neuropathy. (3) Patients with IgM PDN usually have predominantly distal and sensory impairment, with prolonged distal motor latencies, and often anti-myelin associated glycoprotein antibodies. (4) IgM PDN sometimes responds to immune therapies. Their potential benefit should be balanced against their possible side-effects and the usually slow disease progression. (5) IgG and IgA PDN may be indistinguishable from chronic inflammatory demyelinating polyradiculoneuropathy, clinically, electrophysiologically, and in response to treatment. (6) For POEMS syndrome, local irradiation or resection of an isolated plasmacytoma, or melphalan with or without corticosteroids, should be considered, with haemato-oncology advice.

European Federation of Neurological Societies/Peripheral Nerve Society Guideline* on management of paraproteinemic demyelinating neuropathies. Report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society

BACKGROUND

Paraprotein-associated neuropathies have heterogeneous clinical, neurophysiological, neuropathological, and hematological features.

OBJECTIVES

The aim of this guideline was to prepare evidence-based and consensus guidelines on the clinical management of patients with both a demyelinating neuropathy and a paraprotein [paraproteinemic demyelinating neuropathy (PDN)].

METHODS

Disease experts and a representative of patients considered references retrieved from MEDLINE and the Cochrane Library and prepared statements that were agreed in an iterative fashion.

RECOMMENDATIONS

In the absence of adequate data, evidence-based recommendations were not possible, but the Task Force agreed on the following good practice points: (1) patients with PDN should be investigated for a malignant plasma cell dyscrasia; (2) the paraprotein is more likely to be causing the neuropathy if the paraprotein is immunoglobulin M (IgM), antibodies are present in serum or on biopsy, or the clinical phenotype is chronic distal sensory neuropathy; (3) patients with IgM PDN usually have predominantly distal and sensory impairment, with prolonged distal motor latencies, and often anti-myelin-associated glycoprotein antibodies; (4) IgM PDN sometimes responds to immunotherapies. Their potential benefit should be balanced against their possible side effects and the usually slow disease progression; (5) IgG and IgA PDN may be indistinguishable from chronic inflammatory demyelinating polyradiculoneuropathy clinically, electrophysiologically, and in response to treatment; and (6) for POEMS syndrome, local irradiation or resection of an isolated plasmacytoma, or melphalan with or without corticosteroids, should be considered, with hemato-oncology advice.

Anti-SGPG antibody in CIDP: nosological position of IgM anti-MAG/SGPG antibody-associated neuropathy

Polyneuropathy with monoclonal gammopathy usually is considered a nosological entity different from chronic inflammatory demyelinating polyneuropathy (CIDP). Criteria proposed by the American Academy of Neurology AIDS Task Force (1991), however, show monoclonal gammopathy to be a condition concurrent with CIDP. The purpose of this study was to clarify the nosological relationship between CIDP and IgM anti-myelin-associated glycoprotein (MAG)/sulfated glucuronyl paragloboside (SGPG)-associated polyneuropathy. We investigated IgM anti-MAG/SGPG antibody in 85 CIDP patients by various methods, then examined the relation of M-protein to the presence of IgM anti-MAG/SGPG antibody. In our large study, 17 (20%) of 85 CIDP patients had high IgM anti-SGPG antibody titers in the enzyme-linked immunosorbent assay. This was confirmed by thin-layer chromatography-immunostaining for IgM anti-SGPG antibody and immunoblotting for IgM anti-MAG antibody. Immunoelectrophoresis and immunofixation, respectively, detected IgM M-protein in 6 (35%) and 13 (76%) of the 17 CIDP patients. We conclude that some patients with IgM anti-MAG/SGPG antibody with or without monoclonal gammopathy may be diagnosed as having CIDP, when patients are diagnosed according to the current CIDP criteria.

Procedures for the evaluation of monoclonal immunoglobulins

A wide variety of techniques are available for the screening, characterization, and quantification of monoclonal proteins. These techniques vary in regard to the expense, skill and intensity of labor involved, and sensitivity for detection of low levels of monoclonal proteins or of those with unusual migration. Detection of monoclonal proteins requires the use of high-resolution electrophoresis (either gel-based or capillary) and immunofixation (or immunosubtraction). Immunoelectrophoresis is not recommended. Urine for detection of monoclonal free light chains should be from 24-hour samples, and the aliquot should be concentrated at least 100-fold prior to electrophoresis and immunofixation. Dipstick and sulfosalicylic acid techniques are not sensitive enough to detect small quantities of monoclonal free light chains and should not be used as screening tests for this purpose.