Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

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.

Type

Journal article

Journal

Brain

Publication Date

08/2002

Volume

125

Pages

1887 - 1895

Keywords

Age of Onset, Autoantibodies, Autoimmune Diseases, Axons, Creatine Kinase, Electromyography, Female, Genetic Variation, Humans, Lung Neoplasms, Male, Middle Aged, Motor Activity, Muscle, Skeletal, Peripheral Nervous System Diseases, Phenotype, Potassium Channels, Voltage-Gated, Retrospective Studies, Thymoma, Thymus Neoplasms