Severe cranial nerve involvement in a patient with monoclonal anti-MAG/SGPG IgM antibody and localized hard palate amyloidosis

Anti-MAG neuropathy: historical aspects, clinical-pathological correlations, and considerations for future therapeutical trials

BACKGROUND

 Patients with anti-MAG neuropathy present with distal demyelinating polyneuropathy, IgM monoclonal gammopathy, and elevated titers of anti-MAG antibodies.

OBJECTIVE

 This paper reviews what is known about the clinical presentation, course, pathophysiology, and treatment of anti-MAG neuropathy, with considerations for the design of therapeutic trials.

METHODS

 A literature review of the medical and scientific literature related to anti-MAG neuropathy, and the design of therapeutic clinical trials in peripheral neuropathy.

RESULTS

 Anti-MAG neuropathy can remain indolent for many years but then enter a progressive phase. Highly elevated antibody titers are diagnostic, but intermediate titers can also occur in chronic inflammatory demyelinating polyneuropathy (CIDP). The peripheral nerves can become inexcitable, thereby masking the demyelinating abnormalities. There is good evidence that the anti-MAG antibodies cause neuropathy. Reduction of the autoantibody concentration by agents that target B-cells was reported to result in clinical improvement in case series and uncontrolled trials, but not in controlled clinical trials, probably due to inadequate trial design.

CONCLUSION

 We propose that therapeutic trials for anti-MAG neuropathy include patients with the typical presentation, some degree of weakness, highly elevated anti-MAG antibody titers, and at least one nerve exhibiting demyelinating range abnormalities. Treatment with one or a combination of anti-B-cell agents would aim at reducing the autoantibody concentration by at least 60%. A trial duration of 2 years may be required to show efficacy. The neuropathy impairment score of the lower extremities (NIS-LL) plus the Lower Limb Function (LLF) score would be a suitable primary outcome measure.

Uncommon Presentation of IgM Monoclonal Gammopathy of Undetermined Significance (MGUS) and Anti-Myelin-Associated Glycoprotein (MAG)-Associated Demyelinating Peripheral Neuropathy as Respiratory Failure: A Case Report

Monoclonal gammopathy of undetermined significance (MGUS) is a premalignant clonal plasma cell disorder characterized by monoclonal immunoglobulins and/or an abnormal free immunoglobulin light chain ratio. MGUS can be associated with immune-mediated neuropathies, including chronic inflammatory demyelinating neuropathy and its variants. Here, we report the case of a 76-year-old male who presented with progressive weakness, initially in the lower extremities and later including the upper extremities. Serum protein electrophoresis and immunofixation identified an IgM kappa monoclonal protein and further testing confirmed high titers of anti-myelin-associated glycoprotein (MAG) antibodies, leading to a diagnosis of anti-MAG-associated demyelinating peripheral neuropathy. The coexistence of MGUS and anti-MAG antibodies requires meticulous diagnosis and management, especially in patients who present with atypical symptoms of the disease.

Paraneoplastic Neuropathies: What's New Since the 2004 Recommended Diagnostic Criteria

The diagnostic criteria published by the PNS (Paraneoplastic Neurological Syndromes) Euronetwork in 2004 provided a useful classification of PNS, including paraneoplastic neuropathies. Subacute sensory neuronopathy (SSN) was the most frequently observed peripheral PNS, whereas other forms of neuropathy, as sensory polyneuropathy, sensorimotor polyneuropathy, demyelinating neuropathies, autonomic neuropathies, and focal nerve or plexus lesions, were less frequent. At the time of publication, the main focus was on onconeural antibodies, but knowledge regarding the mechanisms has since expanded. The antibodies associated with PNS are commonly classified as onconeural (intracellular) and neuronal surface antibodies (NSAbs). Since 2004, the number of antibodies and the associated tumors has increased. Knowledge has grown on the mechanisms underlying the neuropathies observed in lymphoma, paraproteinemia, and multiple myeloma. Moreover, other unrevealed mechanisms underpin sensorimotor neuropathies and late-stage neuropathies, where patients in advanced stages of cancer—often associated with weight loss—experience some mild sensorimotor neuropathy, without concomitant use of neurotoxic drugs. The spectrum of paraneoplastic neuropathies has increased to encompass motor neuropathies, small fiber neuropathies, and autonomic and nerve hyperexcitability syndromes. In addition, also focal neuropathies, as cranial nerves, plexopathies, and mononeuropathies, are considered in some cases to be of paraneoplastic origin. A key differential diagnosis for paraneoplastic neuropathy, during the course of cancer disease (the rare occurrence of a PNS), is chemotherapy-induced peripheral neuropathy (CIPN). Today, novel complications that also involve the peripheral nervous system are emerging from novel anti-cancer therapies, as targeted and immune checkpoint inhibitor (ICH) treatment. Therapeutic options are categorized into causal and symptomatic. Causal treatments anecdotally mention tumor removal. Immunomodulation is sometimes performed for immune-mediated conditions but is still far from constituting evidence. Symptomatic treatment must always be considered, consisting of both drug therapy (e.g., pain) and attempts to treat disability and neuropathic pain.

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.

Asymmetrical and Isolated Hypoglossal Nerve Palsy Accompanied by a New Subset of Anti-ganglioside Antibodies in a Patient with Diffuse Large B Cell Lymphoma

Malignant lymphoma sometimes involves peripheral nerves due to paraneoplastic syndrome associated with anti-ganglioside antibodies. We report a very rare case of malignant lymphoma accompanied by an asymmetrical and isolated hypoglossal nerve palsy associated with a new subset of anti-ganglioside antibodies. Magnetic resonance imaging and ¹⁸F-2-deoxy-2-fluoro-D-glucose position emission tomography showed no abnormalities of the hypoglossal nerve nucleus; however, the patient' s serum was positive for anti-sulfated glucuronyl paragloboside IgM antibodies as well as anti-GM1 IgM and anti-GQ1b IgM antibodies. The present case might suggest a paraneoplastic asymmetrical and isolated hypoglossal nerve palsy associated with a new subset of anti-ganglioside antibodies.

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

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

The clinical spectrum of IgM-related amyloidosis: a French nationwide retrospective study of 72 patients

Immunoglobulin M (IgM)-related amyloidosis remains a rare and little-known complication of monoclonal IgM-associated disorders. We sought to determine the clinical and laboratory presentation, response to treatment, and outcome of patients with IgM-related amyloidosis in the era of new therapeutic approaches. We conducted a retrospective study in 29 French centers to identify patients with monoclonal IgM and biopsy-proven amyloidosis; we reviewed patients' records and collected relevant clinical and laboratory data. We identified 72 patients with IgM-related amyloidosis. Systemic primary amyloidosis (AL) was present in 64, peritumoral AL in 5, and systemic secondary amyloidosis (AA) in 3 patients. A peculiar pattern of relatively frequent lymph node (31%) and lung (17%) involvement was noted in patients with systemic AL amyloidosis. Response to alkylating agents was poor, with a hematologic response in 37%, a complete remission in 0%, and an organ response in 21%. Response to hematopoietic stem cell transplantation showed a hematologic response in 100% with complete remission in 75% and an organ response in 75%. Purine analogs and rituximab induced a hematologic response in 73% and 60%, respectively, with complete remission in 9% and 0% and an organ response in 55% and 0%, respectively. In multivariate analysis, prognostic factors for survival were serum albumin level < or =3.5 g/dL (p = 0.018) and heart involvement (p = 0.0034). Further prospective studies are needed in patients with IgM-related amyloidosis, with special emphasis on treatment options: hematopoietic stem cell transplantation and purine analogs could represent the most effective therapies. The identification of adverse prognostic factors of survival could be useful for those managing and making treatment decisions for these patients.