Abstract
Neuromyotonia is a heterogeneous group of genetic and autoimmune channelopathies resulting in hyperexcitability of peripheral nerves. We report an unusual case of neuromyotonia, which to our knowledge has not been previously described. The patient developed intermittent attacks of severe painful muscle stiffness accompanied by sweating, myokymia and raised serum creatine kinase. Genetic analysis of KCNA1, KCNQ2 and SCN4A genes did not identify pathogenic mutation. Serum voltage-gated potassium channel antibody was also negative. He was successfully treated with acetazolamide and carbamazepine. This appears to be a new neuromuscular disease, “paroxysmal neuromyotonia”, the etiology of which is still unknown.
Highlights
Neuromyotonia is characterized by muscle stiffness and cramps, myokymia, and pseudomyotonia in association with continuous motor unit activity [1]
Recent study demonstrated that VGKC antibodies did not bind to Kv1 subunits but its major target was contactin-associated protein-2 (CASPR2) [3]
We report a unique patient with clinical and electrophysiological features of neuromyotonia including myokymia, muscle stiffness and continuous motor unit activity in association with autonomic dysfunction
Summary
Neuromyotonia is characterized by muscle stiffness and cramps, myokymia, and pseudomyotonia in association with continuous motor unit activity [1]. Most cases are considered to be autoimmune-mediated usually related to voltage-gated potassium channel (VGKC)-complex antibodies [2]. Recent study demonstrated that VGKC antibodies did not bind to Kv1 subunits but its major target was contactin-associated protein-2 (CASPR2) [3]. CASPR2 is co-localized with Kv1.1 and 1.2 at the juxtaparanodes in myelinated axons. It is possible that antibodies to CASPR2 cause down-regulation of CASPR2/Kv1.1/Kv1.2 complexes resulting in hyperexcitability of peripheral nerves [3]. Patients with a rare inherited form often develop myokymia as a part of. Address: Division of Neurology, Department of Medicine, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, 270 Rama 6 Road, Bangkok 10400, Thailand.
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