Multiple sclerosis and non-dystrophic myotonias: do they share a common pathophysiology?

Some patients with multiple sclerosis (MS) complain of symptoms, such as myokymia, myotonia, spasms, and stiffness, which have been demonstrated to be due to a concurrent non-dystrophic myotonia, i.e. myotonia congenita or paramyotonia congenita. Beyond the known casual association between MS and non-dystrophic myotonia, a channelopathy representing a primary trait of MS rather than an epiphenomenon of demyelization (i.e., an acquired channelopathy) may exist. Indeed, the finding of MS patients with no genetic evidence of non-dystrophic myotonia but showing a clinical picture resembling this condition would support this hypothesis. Thirty patients with MS and no concurrent diagnosis of myotonia congenita or paramyotonia congenita were submitted to the Fournier protocol. Some of these MS patients presented abnormal muscle excitability with scarce myotonic discharges, but only a few of them had clinical features compatible with myotonia congenita or paramyotonia congenita syndromes. Even though the low number of recruited patients did not allow a robust statistical analysis, our data seemed to indicate the presence of an ion channel dysfunction that is independent of the acquired channelopathies and likely represents a common pathophysiological mechanism underlying a unique channelopathy simultaneously involving the peripheral and the central nervous system in individuals with MS. Confirming the presence of such a primary channelopathy in MS patients is of non-negligible importance, since dysfunction of ion channels may represent a suitable therapeutic target in MS.