Impaired neuromuscular transmission and response to acetylcholinesterase inhibitors in centronuclear myopathies.

Many clinical features of autosomal centronuclear myopathies (CNM) and X-linked myotubular myopathy (XLMTM) are common to congenital myasthenic syndromes (CMS). We describe three children whose clinical and electrophysiological findings originally suggested CMS, in whom CNM was diagnosed pathologically, though not yet genetically characterised. A fourth case, with XLMTM, also showed electrophysiological features of a neuromuscular transmission defect. Three (including the XLMTM case) showed improved strength with acetylcholinesterase inhibitor treatment. We also studied neuromuscular junction structure and function in the MTM1 knockdown zebrafish model of XLMTM, demonstrating abnormal neuromuscular junction organization; anticholinesterase therapy resulted in marked clinical response. These observations suggest that a neuromuscular transmission defect may accompany CNM and contribute to muscle weakness. Muscle biopsy should be considered in infants suspected to have CMS, especially if treatment response is incomplete, or no CMS gene mutation is identified. Treatment with acetylcholinesterase inhibitors may benefit some CNM patients. This warrants further confirmation.

Characteristics of fasciculations in amyotrophic lateral sclerosis and the benign fasciculation syndrome.

The aim of this study was to determine first, if benign fasciculations and those in amyotrophic lateral sclerosis can de distinguished on the basis of their waveforms or firing characteristics, and second to determine how fasciculation parameters evolved with progression of amyotrophic lateral sclerosis. Fasciculation potentials recorded from 63 muscles of 28 patients with definite amyotrophic lateral sclerosis were compared with those from 21 muscles of 11 patients with the benign fasciculation syndrome. In each muscle, at a single site, up to 15 identifiable fasciculation potentials could be recognized. Thus the characteristics of 430 fasciculations from patients with amyotrophic lateral sclerosis and 191 benign fasciculations were analysed. Fasciculation potential amplitude, area, turns, duration, firing interval, indices of waveform variability, evidence of axonal conduction block, evidence of axonal conduction variability and propensity to produce double fasciculations were measured. The waveforms of fasciculations in amyotrophic lateral sclerosis were on average of shorter duration and had a greater number of turns than benign fasciculations, but, although irregular in both conditions, the firing rate in amyotrophic lateral sclerosis was significantly higher. In both conditions, there was evidence of multifocal distal generation of fasciculations, axonal conduction block in the motor unit arborization and of variable axonal conduction. When severe weakness and marked chronic neurogenic change were present on electromyography, the firing rate of fasciculations in amyotrophic lateral sclerosis was higher but fasciculation potential amplitude, area and indices of waveform variability were little changed. Double fasciculations in which the waveforms of the two potentials were the same occurred in both conditions. The intervals were in two bands: an early band with 4-10 ms intervals showed identical waveforms of the two potentials, indicating the region of generation was the same. A second band of double fasciculation occurred in the tibialis anterior at an interval of 30-50 ms. Here, the first fasciculation waveform was variable in shape but the second fasciculation was the same on each occasion, suggesting reactivation of the fasciculation via the F-wave route. Double fasciculations in which the second discharge was different from the first had flat time-interval histograms, indicating no interaction between different fasciculations. In conclusion, benign and malignant fasciculations are not distinguishable on the basis of waveform; highly complex fasciculation potentials can be seen in both conditions. Fasciculation firing rate and the frequency of double fasciculations increases in amyotrophic lateral sclerosis when there is a marked lower motor neuron abnormality.

Amyotrophic lateral sclerosis with sensory neuropathy: part of a multisystem disorder?

Sensory involvement is thought not to be a feature of amyotrophic lateral sclerosis (ALS). However, in the setting of a specialist motor neuron disease clinic, we have identified five patients with sporadic ALS and a sensory neuropathy for which an alternative cause could not be identified. In three individuals, sensory nerve biopsy was performed, demonstrating axonal loss without features of an alternative aetiology. These findings support the hypothesis that ALS is a multisystem neurodegenerative disorder that may occasionally include sensory neuropathy among its non-motor features.

Multifocal acquired demyelinating sensory and motor neuropathy presenting as a peripheral nerve tumor.

A man with multifocal acquired demyelinating sensory and motor neuropathy (MADSAM), or Lewis-Sumner syndrome, presented with a progressive left lumbosacral plexus lesion resembling a neurofibroma. After 7 years he developed a left ulnar nerve lesion with conduction block in its upper segment. Treatment with intravenous immunoglobulin improved the symptoms and signs of both lesions. We conclude that inflammatory neuropathy must be considered in the differential diagnosis of peripheral nerve tumors, and that unifocal lesions may precede multifocal involvement in MADSAM by several years. In addition, we discuss the clinical features in 9 patients attending a specialist peripheral nerve clinic and review the literature.

Phenotypic variants of autoimmune peripheral nerve hyperexcitability.

Clinicians use many terms including undulating myokymia, neuromyotonia, Isaacs' syndrome and Cramp-Fasciculation Syndrome to describe the motor manifestations of generalized peripheral nerve hyperexcitability (PNH). Our previous findings in a selected group of patients with undulating myokymia or neuromyotonia, and EMG doublet or multiplet ('myokymic') motor unit discharges, indicated that an autoantibody-mediated potassium channelopathy was likely to be the cause of their disorder. This prompted us to search for a common pathogenesis in a wider spectrum of PNH syndromes. We studied the clinical, autoimmune and electrophysiological features of 60 patients presenting with acquired PNH. Patients were grouped according to an EMG criterion: the presence (group A, n = 42) or absence (group B, n = 18) of doublet or multiplet myokymic motor unit discharges. The average ages of onset in the two groups were 45 and 48 years respectively. The relative frequency and topography of the clinical features were similar in both groups. Serum voltage-gated potassium channel (VGKC) antibodies were detected using a (125)I-alpha-dendrotoxin immunoprecipitation assay in 38% of group A and in 28% of group B. Autoimmune disease and other autoantibodies were present in both groups more frequently than would be expected by chance (59 and 28%, respectively)-particularly myasthenia gravis and acetylcholine receptor (AChR) antibodies. The neurological disorder in both groups could occur as a paraneoplastic condition. Thymoma was detected in 19 and 11%, respectively, and lung cancer in 10 and 6%, respectively. An axonal neuropathy was present in six (14%) of group A and in one (6%) of group B patients. Thus, despite the discrete EMG distinction, both groups share clinical features often associated with autoimmune-related diseases, which can occur as paraneoplastic disorders and, importantly, have an increased frequency of VGKC antibodies. We conclude that autoimmunity, and specifically VGKC antibodies in many cases, are strongly implicated in the pathogenesis of both groups, and that the EMG features reflect quantitative rather than qualitative differences between the diverse clinical syndromes. These findings also have relevance for disease management. A classification is proposed that distinguishes immune-mediated PNH (irrespective of whether VGKC antibodies are detectable by standard assays) from non-immune forms of PNH that include toxins, anterior horn cell degeneration in motor neurone disease and genetic disorders.