Value of short exercise and short exercise with cooling tests in diagnosis of recessive form of myotonia congenita (Becker disease) - are sex differences important?

INTRODUCTION: In myotonia congenita (MC), activation with exercise or cooling can induce transient changes in compound motor action potential (CMAP) parameters, thus providing a guide to genetic analysis. MATERIAL AND METHODS: We performed the short exercise test (SET) and the short exercise test with cooling (SETC) in 30 patients with genetically confirmed Becker disease (BMC) to estimate their utility in the diagnosis of BMC. RESULTS: Although we observed a significant decrease in CMAP amplitude immediately after maximal voluntary effort in both tests in the whole BMC group, in men this decline was significantly smaller than in women, especially in SET. Clinical implications/future directions: In men with a clinical suspicion of BMC, a small decrease in CMAP amplitude in SET together with a typical decline in SETC does not exclude the diagnosis of BMC. Our results show a sex-specific difference in chloride channel function in BMC, which needs further investigation.

The needle EMG findings in myotonia congenita.

INTRODUCTION: Myotonia congenita (MC) is caused by pathogenic variants in the CLCN1 gene coding the chloride channel protein. METHODS: To test the hypothesis that needle EMG could be helpful in distinguishing between the recessive and dominant MC, we performed EMG examination in 36 patients (23 men) aged 4-61 years with genetically proven MC: in 30 patients with autosomal recessive MC (Becker MC) and in 6 with autosomal dominant MC (Thomsen MC). RESULTS: Myotonic discharges were recorded in 95.8% of examined muscles. For the whole MC group we observed a significant positive correlation between parameters of motor unit activity potentials (MUAPs) in vastus lateralis and tibialis anterior muscles and the duration of the disease. Similar correlation for biceps brachii also was found in Becker MC subgroup only. DISCUSSION: EMG could still be helpful in diagnosis of MC and together with provocative tests might be useful in differentiation between recessive and autosomal MC.

Electromyographic findings in sporadic inclusion body myositis.

INTRODUCTION: Clinically oriented diagnostic criteria can be as specific for diagnosis of sporadic inclusion body myositis (sIBM) as pathological criteria, especially at the time of presentation. EMG may provide an convincing proof that a muscle biopsy should be performed. AIMS: To compare the EMG results in patients with sIBM divided into subgroups based on the newest ENMC criteria for sIBM and to obtain the utility of EMG in the diagnostic process at the time of presentation. METHODS: We retrospectively analysed 16 patients with sIBM for motor unit action potential (MUAP) morphology as well as occurrence and distribution of abnormal spontaneous activity (SA) in muscles. RESULTS: Abnormal SA was recorded in 62.5% of sIBM patients. We found statistically significant differences between subgroups in the incidence of polyphasic MUAPs and high amplitude outliers which were more commonly seen in the "clinico-pathologically defined sIBM". Duration of MUAP in the tibialis anterior was significantly shorter in "probable sIBM". DISCUSSION: "Pseudo-neurogenic" MUAPs, mainly in lower limb muscles, are more commonly seen in "clinico-pathologically defined sIBM" while myopathic MUAPs with prominent abnormal SA are recorded in patients diagnosed with "probable sIBM". Both EMG patterns may be suggestive of sIBM and be an indication for further diagnosis.

Abnormal spontaneous activity in primary myopathic disorders.

INTRODUCTION: Reproducible non-insertional spontaneous activity (SA), with the exception of endplate activity, is an unequivocal sign of abnormality and is one of the most useful findings obtained on electromyography. METHODS: In this retrospective study we analyzed occurrence and distribution of abnormal SA in 151 patients with genetically confirmed myopathies. RESULTS: Complex repetitive discharges (CRDs) occurred more frequently than fibrillation potentials (fibs) and positive sharp waves (PSWs) in centronuclear myopathy (CNM) and limb-girdle muscular dystrophy type 2A (LGMD-2A), whereas fibs/PSWs were observed more often in desminopathy and facioscapulohumeral dystrophy (FSHD). Abnormal SA was commonly found in CNM (66.7%) and desminopathy (61.5%), occasionally in Duchenne (DMD) and Becker muscular dystrophy (BMD) (45.2% and 27.6%, respectively), but rarely in FSHD (14.9%) and LGMD-2A (12.0%). CONCLUSIONS: Abnormal SA probably occurs more frequently in disorders associated with structural changes in muscle fibers. Screening for SA may be a valuable tool for diagnosis of non-myotonic myopathies. Muscle Nerve 56: 427-432, 2017.

Are electrophysiological criteria useful in distinguishing childhood demyelinating neuropathies?

Childhood chronic inflammatory demyelinating polyneuropathy (CIDP) needs to be differentiated from hereditary neuropathy. We aimed to validate existing CIDP nerve conduction study (NCS) criteria in a group of children with demyelinating neuropathies of chronic or subacute onset. Retrospective analysis of clinical and NCS results in 18 children with CIDP, 7 with hereditary neuropathy with pressure palsy (HNPP), and 24 with Charcot-Marie-Tooth 1a (CMT1a). AAN and EFNS electrodiagnostic CIDP criteria were fulfilled in 17 of 18 CIDP, 3 of 7 HNPP, and 23 of 24 CMT1a patients. A distal compound muscle action potential (dCMAP) of >9 ms was observed in 14 of 18 CIDP patients but not in any patients with HNPP. Abnormal median/normal sural SNAP (AMNS) and a 10 m/s difference between conduction velocities (CV) of two corresponding nerves were not observed in any CMT1a patients. NCS in CMT1a, HNPP, and CIDP reflect demyelination. dCMAP duration, sensory AMNS, and a 10 m/s CV difference parameter are most useful in the differential diagnosis of pediatric CIDP.

Peripheral nerve involvement in myotonic dystrophy type 2 - similar or different than in myotonic dystrophy type 1?

INTRODUCTION: Multisystem manifestations of myotonic dystrophies type 1 (DM1) and 2 (DM2) are well known. Peripheral nerve involvement has been reported in DM1 but not in genetically confirmed DM2. The aim of our study was to assess peripheral nerve involvement in DM2 using nerve conduction studies and to compare these results with findings in DM1. METHODS: We prospectively studied patients with genetically confirmed DM2 (n=30) and DM1 (n=32). All patients underwent detailed neurological examination and nerve conduction studies. RESULTS: Abnormalities in electrophysiological studies were found in 26.67% of patients with DM2 and in 28.13% of patients with DM1 but the criteria of polyneuropathy were fulfilled in only 13.33% of patients with DM2 and 12.5% of patients with DM1. The polyneuropathy was subclinical, and no correlation was found between its presence and patient age or disease duration. CONCLUSIONS: Peripheral nerves are quite frequently involved in DM2, but abnormalities meeting the criteria of polyneuropathy are rarely found. The incidence of peripheral nerve involvement is similar in both types of myotonic dystrophy.

Does quantitative EMG differ myotonic dystrophy type 2 and type 1?

Genetic testing is considered the only reliable diagnostic approach in myotonic dystrophy. However it has recently been reported that a considerable number of patients with genetically proven types of the disease have unusual phenotypic presentation. The aim of our study was to evaluate motor unit reorganization reflected by various electrophysiological abnormalities in myotonic dystrophies and to compare findings between type 1 (DM 1) and type 2 myotonic dystrophy (DM2). Quantitative electromyography (EMG) recordings in 63 patients (33 with DM1 and 30 with DM2) from the biceps brachii (BB), rectus femoris (RF), first dorsal interosseus (FDI), and tibialis anterior (TA) muscles were analyzed. Mean amplitude and size index (SI) of motor unit potentials recorded in TA and RF muscles, mean potential duration in TA, and mean SI and the number of outliers with amplitude above the normal range in BB were significantly increased in DM2 as compared to DM1. Myotonic discharges were recorded more frequently in DM1 than in DM2. EMG findings significantly differ between DM1 and DM2. The presence of high amplitude potentials in lower limb muscles in DM2 patients, atypical for myogenic muscle lesions, could be explained by muscle fiber hypertrophy observed in muscle biopsies.

Value of short exercise and short exercise with cooling tests in the diagnosis of myotonic dystrophies (DM1 and DM2).

INTRODUCTION: Standard electromyography (EMG) is useful in the diagnosis of myotonic dystrophy type 1 (DM1) and type 2 (DM2), but it does not differentiate between them. The aim of this study was to estimate the utility of the short exercise test (SET) and short exercise test with cooling (SETC) in differentiating between DM1 and DM2. METHODS: SET and SETC were performed in 32 patients with DM1 (mean age 35.8 ± 12.7 years) and 28 patients with DM2 (mean age 44.5 ± 12.5 years). RESULTS: We observed a significant decline in compound motor action potential (CMAP) amplitude in DM1 with both SET and SETC immediately after effort. In DM2, there was no marked change in CMAP amplitude with either SET or SETC. CONCLUSIONS: SET and SETC may serve as useful tools for clinical differentiation between DM1 and DM2, and they may be used as a guide for molecular testing.