Rati Choksi

Treatment of IgM antibody associated polyneuropathies using rituximab

Objectives: Polyneuropathies with associated serum IgM antibodies are often difficult to treat. Rituximab is a monoclonal antibody directed against the B cell surface membrane marker CD20. Rituximab eliminates B cells from the circulation, and, over time, could reduce cells producing autoantibodies. This study tested the ability of rituximab to produce changes in serum antibody titres, and improvement in strength, in patients with neuromuscular disorders and IgM autoantibodies. Methods: Over a period of two years, the authors evaluated changes in strength, measured by quantitative dynamometry, and concentrations of several types of serum antibodies in patients with polyneuropathies and serum IgM autoantibodies. Twenty one patients treated with rituximab were compared with 13 untreated controls. Results: Treatment with rituximab was followed by improved strength (an increase of mean (SEM) 23% (2%)of normal levels of strength), a reduction in serum IgM autoantibodies (to 43% (4%) of initial values), and a reduction in total levels of IgM (to 55% (4%) of initial values). There was no change in levels of serum IgG antibodies. There were no major side effects, even though B cells were virtually eliminated from the circulation for periods up to two years. Conclusions: In patients with IgM autoantibody associated peripheral neuropathies, rituximab treatment is followed by reduced serum concentrations of IgM, but not IgG, antibodies, and by improvement in strength. Additional studies, with placebo controls and blinded outcome measures, are warranted to further test the efficacy of rituximab treatment of IgM associated polyneuropathies.

Multifocal motor neuropathy Serum IgM anti-GM1 ganglioside antibodies in most patients detected using covalent linkage of GM1 to ELISA plates

IgM anti-GM1 antibodies occur with increased frequency in the serum of patients with multifocal motor neuropathy (MMN). We tested the ability of serum IgM from patients with MMN to bind to GM1 ganglioside covalently bound to secondary amino groups on ELISA plates (Co-GM1). The Co-GM1 technique detected high titer (>1,800), selective, serum IgM binding to GM1 ganglioside in 85% of our MMN patients (23/27), a significantly greater frequency compared with figures of 37% and 52% found using our previous testing methods. Selective IgM anti-GM1 antibodies showed disease specificity. The only other patients with selective, high-titer IgM anti-GM1 antibodies had either chronic motor neuropathy without conduction block or acute immune neuropathy in China. No patient from the amyotrophic lateral sclerosis, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré, or systemic immune disorder control groups had selective IgM anti-GM1 antibodies at titers greater than 1,800 detected using Co-GM1 ganglioside as ELISA antigen. Titers of IgM anti-GM1 antibodies in MMN(averaging 31,000 ± 15,000) were more than fourfold higher with Co-GM1 than with previous anti-GM1 assay methods, using conventional ELISA plates with GM-1 antigen alone (7,200 ± 4,400) or in a lipid environment(3,600 ± 1,300). We conclude that using ELISA testing with Co-GM1 antigen, serum anti-GM1 autoantibodies are a useful marker for MMN, because they are present in 85% of MMN patients and, at titers greater than 1,800, have strong specificity for immune-mediated motor neuropathies.

Whole-body energy metabolism and skeletal muscle biochemical characteristics

A low metabolic rate for a given body size and a low fat versus carbohydrate oxidation ratio are known risk factors for body weight gain, but the underlying biological mechanisms are poorly understood. Twenty-four-hour energy expenditure (24EE), sleeping metabolic rate (SMR), 24-hour respiratory quotient (24RQ), and forearm oxygen uptake were compared with respect to the proportion of skeletal muscle fiber types and the enzyme activities of the vastus lateralis in 14 subjects (seven men and seven women aged 30 +/- 6 years [mean +/- SD], 79.1 +/- 17.3 kg, 22% +/- 7% body fat). The following enzymes were chosen to represent the major energy-generating pathways: lactate dehydrogenase (LDH) and phosphofructokinase (PFK) for glycolysis; citrate synthase (CS) and beta-hydroxyacl-coenzyme A dehydrogenase (beta-OAC) for oxidation; and creatine kinase (CK) and adenylokinase (AK) for high-energy phosphate metabolism. Forearm resting oxygen uptake adjusted for muscle size correlated positively with the proportion of fast-twitch muscle fibers (IIa: r = .55, P = .04; IIb: r = .51, P = .06) and inversely with the proportion of slow oxidative fibers (I: r = -.77, P = .001). 24EE and SMR adjusted for differences in fat-free mass, fat mass, sex, and age correlated with PFK activity (r = .56, P = .04 and r = .69, P = .007, respectively). 24RQ correlated negatively with beta-OAC activity (r = -.75, P = .002). Our findings suggest that differences in muscle biochemistry account for part of the interindividual variability in muscle oxygen uptake and whole-body energy metabolism, ie, metabolic rate and substrate oxidation.

Peripheral neuropathies in Waldenström’s macroglobulinaemia

Objective: We sought to determine the prevalence, clinical features, and laboratory characteristics of polyneuropathies in Waldenström’s macroglobulinaemia (WM), a malignant bone marrow disorder with lymphocytes that produce monoclonal IgM. Methods: We prospectively studied 119 patients with WM and 58 controls. Medical history was taken, and neurological examinations, electrodiagnostic tests, and serum studies were performed by different examiners who were blinded to results except the diagnosis of WM. Results: Polyneuropathy symptoms, including discomfort and sensory loss in the legs, occurred more frequently (p<0.001) in patients with WM (47%) than in controls (9%). Patients with WM had 35% lower quantitative vibration scores, and more frequent pin loss (3.4 times) and gait disorders (5.5 times) than controls (all p<0.001). Patients with IgM binding to sulphatide (5% of WM) had sensory axon loss; those with IgM binding to myelin associated glycoprotein (MAG) (4% of WM) had sensorimotor axon loss and demyelination. Patients with WM with IgM binding to sulphatide (p<0.005) or MAG (p<0.001) had more severe sensory axon loss than other patients with WM. Demyelination occurred in 4% of patients with WM with no IgM binding to MAG. Age related reductions in vibration sense and sural SNAP amplitudes were similar (∼30%) in WM and controls. Conclusions: Peripheral nerve symptoms and signs occur more frequently in patients with WM than controls, involve sensory modalities, and are often associated with gait disorders. IgM binding to MAG or sulphatide is associated with a further increase in the frequency and severity of peripheral nerve involvement. Age related changes, similar to those in controls, add to the degree of reduced nerve function in patients with WM.

Vascular pathology in dermatomyositis and anatomic relations to myopathology

The causes of perifascicular myofiber atrophy and capillary pathology in dermatomyositis are incompletely understood. We studied 11 dermatomyositis muscles by histochemistry, immunohistochemistry, and ultrastructure. We found that endomysial capillaries within regions of perifascicular atrophy are not entirely lost, but they have reduced size, endothelial loss, C5b9 complement deposits, and relatively preserved connective tissue molecules and pericytes. In all muscles, the perimysium varies regionally. Some areas contain intermediate‐sized vessels. Others are avascular. In dermatomyositis, vascular perimysium contains abnormal vessel fragments, perivascular inflammation, and increased PECAM‐1. Perifascicular myofiber atrophy and capillary pathology are concentrated near the avascular perimysium. We conclude that both perimysial intermediate‐sized vessels and endomysial capillaries within regions of perifascicular myofiber atrophy are abnormal in dermatomyositis. Capillary damage and myofiber atrophy are concentrated in regions distant from intermediate‐sized perimysial vessels. Chronic immune vascular damage and insufficiency in dermatomyositis may cause ischemia, myofiber atrophy, and capillary damage in “watershed” regions of muscle near the avascular perimysium. Muscle Nerve, 2010

Multifocal motor neuropathy: Serum IgM binding to a GM1 ganglioside‐containing lipid mixture but not to GMl alone

IgM anti-GM1 antibodies are associated with motor neuropathy syndromes, including multifocal motor neuropathy (MMN). We compared the ability of serum IgM from patients with multifocal motor neuropathy to bind to GM1 ganglioside alone and to GM1 as a component of a lipid mixture that also contained galactocerebroside and cholesterol (GGC). Our results showed that high-titer selective serum IgM binding to GGC has strong specificity for MMN. Further, over 40% more serums from patients with MMN have high-titer serum IgM binding to GGC than to GM1 alone. The specific composition and structure of the lipid mixture altered the ability of serum IgM to bind to GMl ganglioside. Substitutions of other lipids for galactocerebroside or cholesterol could completely inhibit the antibody binding. We conclude that serum IgM anti-GGC autoantibodies have specificity for MMN and their binding is strongly influenced by the lipid environment of GM1 ganglioside.

Myopathy with anti-HMGCR antibodies: Perimysium and myofiber pathology

Objective: To analyze clinical features and myopathology changes in muscle fibers, connective tissue, and vessels in 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody–associated myopathies. Methods: Retrospective review of records and myopathologic features of 49 consecutive patients with myopathies and serum HMGCR antibodies. Results: Clinical features included onset age from 12 to 83 years, female predominance (67%), proximal, symmetric weakness (84%), muscle discomfort (78%), dysphagia (35%), systemic features, including skin rash and interstitial lung disease (37%), statin use (38%), and a high serum creatine kinase (83%). Myopathology included muscle fiber necrosis or regeneration (66%), myonuclear pathology (43%), perimysial connective tissue damage (61%), and lymphocytic foci (27%). Conclusions: Patients with HMGCR antibody–associated myopathies present with weakness and muscle discomfort and often have damage to both perimysial connective tissue and muscle fibers, with necrosis and myonuclear pathology. Only a minority of patients with HMGCR antibody–associated myopathies have a history of statin exposure.

Motor neuropathies and serum IgM binding to NS6S heparin disaccharide or GM1 ganglioside

Background Serum IgM binding to GM1 ganglioside (GM1) is often associated with chronic acquired motor neuropathies. This study compared the frequency and clinical associations of serum IgM binding to a different antigen, a disulphated heparin disaccharide (NS6S), with results of IgM binding to GM1. Methods Serums and clinical features were retrospectively compared from 75 patients with motor neuropathies and 134 controls with amyotrophic lateral sclerosis (ALS), chronic immune demyelinating polyneuropathy (CIDP) and sensory neuropathies. Clinical correlations of positive IgM anti-GM1 testing found in 27 of 2113 unselected serums were also reviewed. Serum testing for IgM binding to NS6S and GM1 used covalent antigen linkage to ELISA plates. Results High titre IgM binding to NS6S and GM1 each occurred in 43%, and to one of the two in 64%, of motor neuropathy patients. Motor neuropathy syndromes were present in 25 of 27 patients with high titre serum IgM binding to GM1 in the unselected serums. IgM anti-GM1 or NS6S antibody related motor neuropathy syndromes usually have asymmetric, predominantly distal, upper extremity weakness. Conclusions IgM binding to NS6S disaccharide is associated with motor neuropathy syndromes and occurs with similar frequency to IgM binding to GM1. Testing for IgM binding to NS6S in addition to GM1 increases the frequency of finding IgM autoantibodies in motor neuropathies from 43% to 64%. High titres of serum IgM binding to GM1, tested with covalent ELISA methodology, have 93% specificity for motor neuropathy syndromes. High titres of serum IgM binding to NS6S have specificity for immune motor neuropathies compared with ALS and CIDP.

Severe sensory ataxia and demyelinating polyneuropathy with IgM anti‐GM2 and GalNAc‐GD1A antibodies

Several polyneuropathy syndromes have been described with polyclonal serum immunoglobulin G (IgG) or immunoglobulin M (IgM) binding to gangliosides GM2 and GalNAc‐GD1a that contain the terminal trisaccharide moiety GalNAc(β1‐4)Gal(α2‐3)NeuAc. We describe the clinical and electrodiagnostic features in two patients with serum IgM monoclonal anti‐GM2 and anti‐GalNAc‐GD1a antibodies. These patients had slowly progressive, panmodal sensory loss with severe sensory ataxia. Electrodiagnostic testing showed demyelinating features. Prominent improvement in gait ataxia occurred after treatment with human immune globulin but not after other immunomodulating therapies. Enzyme‐linked immunoabsorbent assay and thin‐layer chromatography demonstrate that the patients serum monoclonal IgM bound to gangliosides GM2 and GalNac‐GD1a but not to gangliosides without the GalNAc(β1‐4)Gal(α2‐3)NeuAc moiety. This neuropathy differs from previously reported neuropathy syndromes associated with polyclonal GM2 and GalNAc‐GD1a antibodies and from other chronic demyelinating polyneuropathies. We conclude that a distinct syndrome of chronic demyelinating neuropathy with sensory ataxia, unresponsive to corticosteroids, is associated with monoclonal IgM binding to gangliosides with a terminal GalNAc(β1‐4)Gal(α2‐3)NeuAc trisaccharide moiety. Diagnosis of this syndrome is important to direct appropriate treatment.

Congenital muscular dystrophy syndromes distinguished by alkaline and acid phosphatase, merosin, and dystrophin staining

Congenital muscular dystrophy syndromes are characterized by congenital weakness, contractures, and dystrophic features on muscle biopsy. However, these syndromes are often difficult to diagnose precisely because their clinical and pathologic characteristics are not specific and resemble changes in other myopathies. We examined muscle biopsies from 20 children with a congenital muscular dystrophy syndrome. Disease controls with dystrophies or other myopathies (n=19) and normal individuals (n=15) were studied for comparison. In each biopsy we determined (1) numbers of muscle fibers with alkaline phosphatase (AlkP) staining, (2) numbers of acid phosphatase-(AcP) positive cells, (3) dystrophin levels by immunocytochemistry, and (4) the distribution of merosin and laminin-A staining. A ratio of AcP:AlkP staining was calculated for each biopsy. In nine patients with congenital muscular dystrophy (younger than 4 years of age) with normal dystrophin, the AcP:AlkP ratio was low (0.09 +/- 0.03). In contrast, in Duchenne muscular dystrophy, the AcP:AlkP ratio was 15 times higher (1.6 +/- 0.04, p=0.001). The three children with congetial muscular dystrophy syndromes and reduced dystrophin and one child with facioscapulohumeral dystrophy had AcP:AlkP ratios in the range of Duchenne muscular dystrophy patients (2.4 +/- 1.4). Low Ac:AlkP ratios were related to relative absence of AcP-positive cells. Merosin staining was absent in 5 of the 17 congenital muscular dystrophy biopsies tested. None of the 5 children with merosin-negative but all 12 with merosin-positive stains walked (p=0.0002). We conclude that a pattern of few AcP-positive cells in the setting of numerous AlkP staining muscle fibers has specificity for congenital muscular dystrophy syndromes and provides histopathologic support for the diagnosis. Reduced merosin in muscle predicts more severe weakness and long-term disability.