Titin antibodies in "seronegative" myasthenia gravis--A new role for an old antigen.

Myasthenia gravis (MG) is an autoimmune disease caused by antibodies targeting the neuromuscular junction of skeletal muscles. Triple-seronegative MG (tSN-MG, without detectable AChR, MuSK and LRP4 antibodies), which accounts for ~10% of MG patients, presents a serious gap in MG diagnosis and complicates differential diagnosis of similar disorders. Several AChR antibody positive patients (AChR-MG) also have antibodies against titin, usually detected by ELISA. We have developed a very sensitive radioimmunoprecipitation assay (RIPA) for titin antibodies, by which many previously negative samples were found positive, including several from tSN-MG patients. The validity of the RIPA results was confirmed by western blots. Using this RIPA we screened 667 MG sera from 13 countries; as expected, AChR-MG patients had the highest frequency of titin antibodies (40.9%), while MuSK-MG and LRP4-MG patients were positive in 14.6% and 16.4% respectively. Most importantly, 13.4% (50/372) of the tSN-MG patients were also titin antibody positive. None of the 121 healthy controls or the 90 myopathy patients, and only 3.6% (7/193) of other neurological disease patients were positive. We thus propose that the present titin antibody RIPA is a useful tool for serological MG diagnosis of tSN patients.

MuSK autoantibodies in myasthenia gravis detected by cell based assay--A multinational study.

Seronegative myasthenia gravis (MG) presents a serious gap in MG diagnosis and understanding. We applied a cell based assay (CBA) for the detection of muscle specific kinase (MuSK) antibodies undetectable by radioimmunoassay. We tested 633 triple-seronegative MG patients' sera from 13 countries, detecting 13% as positive. MuSK antibodies were found, at significantly lower frequencies, in 1.9% of healthy controls and 5.1% of other neuroimmune disease patients, including multiple sclerosis and neuromyelitis optica. The clinical data of the newly diagnosed MuSK-MG patients are presented. 27% of ocular seronegative patients were MuSK antibody positive. Moreover, 23% had thymic hyperplasia suggesting that thymic abnormalities are more common than believed.

Antititin antibody in early- and late-onset myasthenia gravis.

OBJECTIVES: Myasthenia gravis (MG) is an autoimmune disease caused by antibodies against neuromuscular junction proteins, 85% of patients have antibodies against acetylcholine receptor (AChR-MG). Antititin antibodies are present in a subset of patients with MG. We aimed to determine the value of antititin antibodies as severity markers and thymoma predictors in early- and late-onset MG. MATERIALS & METHODS: Two-hundred and ninety-five consecutive MG patients (188 F and 107 M) aged 12-89 years (mean 50y) were included. 164 patients had early-onset (EOMG, ≤50 years of age), 131 had late-onset MG (LOMG). Twenty-six patients had thymoma. symptoms, severity graded with MGFA scale, thymus histology, medications, and treatment results were analyzed. RESULTS: Antititin antibodies were present in 81 (27%) of all patients: 54% of thymoma MG, 0.6% of non-thymomatous EOMG, and 55% of LOMG, with proportion of titin-positive patients increasing linearly from 40% in the 6th to 88% in the 9th decade of life. Titin-positive patients had more bulbar symptoms (P = 0.003). Severity of MG, need for immunosuppression, myasthenic crisis risk or treatment results were not related to its presence. Antititin antibodies had 56% sensitivity, 99% specificity, 90% positive predictive value (PPV), and 95% negative predictive value (NPV) for thymoma diagnosis in EOMG, and 50% sensitivity, 75% specificity, 71% PPV and 55% NPV in LOMG. CONCLUSIONS: Antititin antibodies have high PPV and NPV for thymoma in EOMG. In MG without thymoma, antititin antibodies can be considered as markers of LOMG, but not of a severe course in our MG cohort.

A comprehensive analysis of the epidemiology and clinical characteristics of anti-LRP4 in myasthenia gravis.

Double-seronegative myasthenia gravis (dSN-MG, without detectable AChR and MuSK antibodies) presents a serious gap in MG diagnosis and understanding. Recently, autoantibodies against the low-density lipoprotein receptor-related protein 4 (LRP4) have been identified in several dSN-MG sera, but with dramatic frequency variation (∼2-50%). We have developed a cell based assay (CBA) based on human LRP4 expressing HEK293 cells, for the reliable and efficient detection of LRP4 antibodies. We have screened about 800 MG patient sera from 10 countries for LRP4 antibodies. The overall frequency of LRP4-MG in the dSN-MG group (635 patients) was 18.7% but with variations among different populations (range 7-32.7%). Interestingly, we also identified double positive sera: 8/107 anti-AChR positive and 10/67 anti-MuSK positive sera also had detectable LRP4 antibodies, predominantly originating from only two of the participating groups. No LRP4 antibodies were identified in sera from 56 healthy controls tested, while 4/110 from patients with other neuroimmune diseases were positive. The clinical data, when available, for the LRP4-MG patients were then studied. At disease onset symptoms were mild (81% had MGFA grade I or II), with some identified thymic changes (32% hyperplasia, none with thymoma). On the other hand, double positive patients (AChR/LRP4-MG and MuSK/LRP4-MG) had more severe symptoms at onset compared with any single positive MG subgroup. Contrary to MuSK-MG, 27% of ocular dSN-MG patients were LRP4 antibody positive. Similarly, contrary to MuSK antibodies, which are predominantly of the IgG4 subtype, LRP4 antibodies were predominantly of the IgG1 and IgG2 subtypes. The prevalence was higher in women than in men (female/male ratio 2.5/1), with an average disease onset at ages 33.4 for females and 41.9 for males. Overall, the response of LRP4-MG patients to treatment was similar to published responses of AChR-MG rather than to MuSK-MG patients.

Lambert-Eaton myasthenic syndrome in childhood.

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction. LEMS can be associated with a variety of neoplasms. Patients present with proximal muscle weakness and fatigability, often combined with areflexia. Only 5% of reported cases are children. We report a case of 11-year old boy with non-neoplastic Lambert-Eaton myasthenic syndrome. Repetitive nerve stimulation test showed 83% increment after maximal voluntary contraction, presence of antibodies against voltage-gated calcium channels confirmed the diagnosis. The boy responded well to immunosuppressive treatment with prednisone and azathioprine and remains cancer-free for 4 years.

MuSK-positive myasthenia gravis is rare in the Polish population.

BACKGROUND AND PURPOSE: MuSK-positive myasthenia gravis (MG) is diagnosed in 0-48% of cases with generalized seronegative MG in different populations. The presence of anti-MuSK antibodies generally relates to a severe course and lack of response to thymectomy. We analyzed for the first time the serology and clinical characteristics of MuSK-positive MG in the Polish population. METHODS: One hundred and fifty-one patients were tested for the presence of anti-AChR and anti-MuSK antibodies: 62 with seronegative MG, including 14 with ocular seronegative MG, 48 age-matched patients with seropositive MG and 41 controls. RESULTS: All patients with seropositive MG and the disease controls were MuSK-negative. Anti-MuSK antibodies were detected only in four patients with seronegative MG (8.7% of generalized seronegative cases): three women and one man. All four had predominantly bulbar involvement, and underwent thymectomy, with no apparent benefit. All of them improved clinically after immunosuppressive treatment with remissions lasting up to 7 years. CONCLUSION: MuSK-positive MG is rare in Polish population accounting for only 8.7% of seronegative cases with generalized MG. This is consistent with emerging evidence for lower MuSK antibodies at more northerly latitudes.

How accurate is spirometry at predicting restrictive pulmonary impairment in children with myasthenia gravis.

Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction. Clinical symptoms are caused by weakness and increased fatigability of various muscle groups. Myasthenia may lead to significant respiratory dysfunction. The aim of our study was to estimate lung function in children with MG. We tested 23 non-smoking patients (18 girls and 5 boys) aged 7-18 years. Whole-body plethysmography and spirometry were performed in all patients. In 33% of the patients a decrease in VC <80% of predicted value was observed (VC = 89 +/-19%), but the analysis of TLC revealed restrictive pattern only in one patient (TLC = 102 +/-17%). In more than 75% of the children the value of RV above 120% of predicted value was found (RV = 146 +/-54%). Spirometric obstructive pattern measured by FEV1%VC <70% was not observed, although in 56% of the patients airway resistance was increased (Raw = 132 +/-44%). In 45% of the patients a decrease of PEF (76 +/-14%) was observed. In MG children true restrictive pulmonary impairment is rarely observed and a decrease in VC in these patents seems to result mainly from functional restriction provoked by an increase in RV. Spirometry is not an optimum method to assess functional changes in MG patients. The assessment of additional measures such as TLC, RV, and Raw is desirable.

Charcot-Marie-Tooth type 4F disease caused by S399fsx410 mutation in the PRX gene.

Charcot-Marie-Tooth type 4F disease (CMT4F) is an autosomal recessive neuropathy caused by mutations in the PRX gene. To date, only seven mutations have been identified in the PRX gene. In this study, the authors report a novel S399fsX410 mutation in the PRX gene and its effects at the protein level, which was identified in an 8-year-old patient with early-onset CMT disease.

A single-fibre EMG study of neuromuscular transmission in migraine patients.

It is known that mutations of CACNA1A, which encodes a neuronal P/Q Ca(2+) channel, are present in patients with familial hemiplegic migraine, and possibly in other types of migraine as well. This calcium channel is also involved in neuromuscular transmission. To assess if the single-fibre EMG (SFEMG) method can demonstrate a neuromuscular transmission deficit in migraine, a group of 26 patients with different types of migraine and 20 healthy control subjects were studied. The migraine patients were divided into three groups: 8 patients with migraine without aura (MoA), 12 with migraine with aura excluding visual aura (MA) and 6 with visual aura (VA). A SFEMG of the voluntarily activated extensor digitorum communis muscle was performed. The SFEMG results were normal in the healthy controls and the MoA group (migraine without aura). Slight neuromuscular transmission disturbances were present in 6/12 (50%) of patients with MA and in 1/6 (17%) of patients with VA. We suggest that abnormal neuromuscular transmission detectable by SFEMG may reflect a genetically determined dysfunction of the P/Q Ca(2+) channels in a subgroup of migraineurs with aura.

Motor unit hyperexcitability in amyotrophic lateral sclerosis vs amino acids acting as neurotransmitters.

OBJECTIVES: Electrophysiological studies of amyotrophic lateral sclerosis (ALS) patients reveal not only lower motor neuron involvement, but also widespread signs of its hyperexcitability. They might be the consequence of changes in the level of amino acids acting as neurotransmitters. MATERIAL AND METHODS: Electrophysiological examination of 31 patients with sporadic ALS was performed. A hyperexcitability index (HI) was created to describe the amount of double discharges, fasciculation potentials or 'giant' F-waves. Glutamate, aspartate, glycine and GABA concentration in serum and cerebrospinal fluid (CSF) were estimated, using the high performance liquid chromatography technique. RESULTS: The electrophysiological studies revealed marked variability in HI in the patients group. HI did not correlate with duration of the disease and the degree of disability expressed with Norris score, as well as with the level of excitatory or inhibitory amino acids in the body fluids. CONCLUSION: Hyperexcitability of the motor unit observed in ALS is not directly related to changes in serum and CSF level of amino acids acting as neurotransmitters.

Clinical, electrophysiological and immunological remissions after thymectomy in myasthenia gravis.

OBJECTIVES: Approximately 50% of patients treated with thymectomy have a chance for symptom-free life. However, immunological and neurophysiological abnormalities may be detected in patients with clinical remission. Although improvement usually parallels decrease in acetylcholine receptor antibody (AChRAb) levels and jitter values, there is a question what factors influence immunological and electrophysiological remission in a population of myasthenia gravis (MG) patients. METHODS: We analyzed retrospectively clinical data of 32 MG patients operated for generalized MG, followed-up at our department for 17.2 (4-31) years. They were in clinical remission for 12.8 (2-25) years. All of them had single fiber electromyograhy (SFEMG) of extensor digitorum communis muscle (EDC) muscle and estimation of AChRAb level at the end of follow-up. Their age at onset of MG was 17 years (6-48) and at thymectomy 19 (6.4-58) years. Tensilon test was positive in 30, repetitive nerve stimulation in 29 cases. RESULTS: Clinical remission was reached on average 4.2 years after thymectomy. SFEMG jitter value normalized in 60% of cases. AChRAb were negative only in 34% of patients. Jitter values correlated with AChRAb levels (P=0.006, r=0.5) but were not related to clinical factors. Only time to thymectomy correlated with time from thymectomy to clinical remission (P=0.001, r=0.5). CONCLUSIONS: Clinical remission is not always accompanied by normalization of SFEMG and AChRAb. Although normalization of neuromuscular transmission in patients with remission of MG is individual, short duration of MG before thymectomy increases the chance of early remission.

Reconsiderations about the abnormalities of somatosensory evoked potentials in motor neuron disease.

The frequency of involvement of sensory pathways in motor neuron disease (MND) remains the matter of controversy. For this reason the purpose of the present work was to test how often sensory system involvement might be detected by somatosensory evoked potentials (SEP) studies and then to verify the presence of alteration of the sensory conduction and to detect the frequency of abnormalities of somatosensory peripheral, spinal, subcortical and cortical potentials in MND. SEP were tested after median nerve stimulation at the wrist, recorded from Erb's point, Ce2, Ce7 and scalp. Pearson's correlation coefficients test and Wilcoxon rank-sum test were used for statistical analysis. 74 patients (22 women and 52 men) were examined. Mean age of patients was 54.07 +/- 11.24 years; mean duration of the disease -19.25 +/- 15.87 months. SEP were abnormal in 39 of 74 patients (about 53%) whereas the sensory NCV in median nerve was abnormal in 14 of 74 patients (19%). The most frequent pattern of abnormalities consisted of the absence or delay of cortical responses. The mean values of SEP latencies (N9, N11, N13, N20 and P25) were significantly increased in MND patients (p < 0.05) as compared with controls. The N9 and N11 latencies correlated with the duration of the disease. The results of our study (concerning a large group of MND patients) suggest that the involvement of sensory pathways is not rare in MND.

[Hereditary sensorimotor neuropathy in electrophysiological studies]. / Dziedziczna czuciowo-ruchowa neuropatia w obrazie elektrofizjologicznym.

We performed clinical and electrophysiological studies in 42 children with hereditary motor and sensory neuropathy type I and II (HMSN I and II) and in 103 members of their families. In 24 families with HMSN I the conduction velocity and latency were markedly changed in the nerves innervating the distal muscles (median, peroneal nerves) as well as proximal muscles (facial, axillary and musculocutaneous nerves). The changes were uniform in all motor and sensory nerves studied in a particular patient. The intensity of changes was similar in members of their families even when the clinical abnormalities were minimal, thus the degree of conduction velocity slowing was uniform within families. In adults with HMSN I (group A i B) we found less marked slowing of nerve conduction as compared to children (group P), the difference being significant (p < 0.001). It may suggest a slow process of peripheral nerves maturation despite the existing morbid condition. In patients of 18 families with HMSN II slight changes in conduction velocity were found only in nerves innervating the distal muscles, more evident in legs (peroneal and sural nerves). Conduction time of facial, axillary and musculo-cutaneous nerves was normal. The values of nerve conduction were not changing with patients' age. We recommend examining conduction time in facial, axillary or musculocutaneous nerve as a useful procedure for differentiation between HMSN I and II, especially in families with borderline conduction values in the nerves innervating distal muscles.

[Median nerve electrophysiological assessment in amyotrophic lateral sclerosis]. / Ocena elektrofizjologiczna nerwu obwodowego w stwardnieniu zanikowym bocznym.

Our material comparises 105 patients (62 men and 43 women) aged 26-73 years with amyotrophic lateral sclerosis (ALS). EMG examination confirmed the diagnosis of multilevel lesion of spinal motor neurons. Clinically, 94 of them had classical ALS, 3 had primary bulbar palsy (PBP), 6 had primary motor spinal atrophy (PSMA), and 2 had primary lateral sclerosis (PLS). Disease duration was 18.1 month, on the average, ranging from 2-60 months. In all patients motor and sensory nerve conduction was studied in median, peroneal and sural nerves. Conduction velocity, distal latency, F-wave latency of motor nerves, amplitude of M response and of sensory potentials were evaluated. Abnormalities were found most often in the motor fibres of median nerve: lowering of the M response amplitude in 44% of nerves studied, slowing of conduction velocity and elongation of distal latency in ca. 30%, elongation of F-wave latency in 27%. In the peroneal nerve the changes were less frequent: 38%, 21%, and 3%, respectively. They were also less marked. In the sensory fibres of median nerve slowing of conduction velocity was found in 25% of nerves, in sural nerve in 11%. Some slight decrease of amplitude of sensory potentials was seen in those nerves. The results obtained indicate a possibility of peripheral nerve lesion in the course of ALS which must be remembered in clinical diagnosing.

Electrophysiological findings in hereditary motor and sensory neuropathy type I and II--a conduction velocity study.

We performed clinical and electrophysiological studies in 42 children with hereditary motor and sensory neuropathy type I and II (HMSN I and HMSN II) and in 103 members of their families. In 24 families with HMSN I the conduction velocity and the latency were markedly changed in the nerves innervating the distal muscles (median, peroneal nerves), as well as proximal muscles (facial, axillary, and musculocutaneous nerves). The changes were uniform in all motor and sensory nerves studied in the particular patient. No nerve conduction worsening with age has been found in cross-sectional analysis. In patients with HMSN I the conduction velocity was impaired even when the clinical abnormalities were minimal. The degree of the conduction velocity slowing was uniform within majority of the families. Homogeneity of conduction velocity slowing in individuals with HMSN I regardless of clinical expression suggests a primary myelin defect as an underlying cause. In patients from 18 families with HMSN II slight changes in conduction velocity were found only in the nerves innervating the distal muscles, the latency of axillary and facial nerves was within normal range. We recommend examining conduction time in facial and axillary nerves as a useful procedure for differentiation between HMSN I and II, especially in families with borderline conduction values in the long nerves.

Sympathetic skin response (SSR) in multiple sclerosis.

The function of the autonomic system in multiple sclerosis (MS) is often afflicted. In order to reveal the presence of autonomic disturbances examination of sympathetic skin response (SSR), as a simple non-invasive method of the evaluation of conduction in autonomic nervous system, was performed in 25 patients with clinically defined MS. The diagnosis was confirmed by MRI and evoked potentials studies. Bimodal type of stimulation was used: the median nerve was stimulated, then the auditory stimulus (burst) was presented to the patient. Responses were recorded simultaneously from the palms and soles. SSR was abnormal in 19 patients (76%). Absence of the response from lower limbs and normal response from upper limbs were found in 6 patients (24%), increase in latency and decrease in amplitude from upper and lower limbs were found in 8 patients (32%) and increase in latency, decrease in amplitude of the response from upper limbs with absence of the response from lower limbs were found in 5 patients (20%). SSR appears to be a simple and effective method of assessing sympathetic disturbances in multiple sclerosis.