The frequency of neuromyotonia in 37 patients previous diagnosed as benign cramp-fasciculation syndrome

Introduction: Neuromyotonia (NM), Isaacs-Zschoke-Mertens syndrome or continuous muscle fiber activity (CMFA), is a rare condition associated to complexes VGKC-antibodies. Clinically, fasciculations, myokymias, muscle stiffness and a myotonic appearance of movements after contraction are typical findings. Rarely, bulbar muscles can be involved, mainly seen as twitching of the tongue, swallowing or speaking problems. Major differential diagnosis is the benign cramp-fasciculation syndrome (BFS), which can also be seen either in healthy people or as motorneuron pre-syndrome. In electromyography, spontaneous irregular discharges can be found frequently with typical di-, tri- or multiplet single motor unit discharges. In up to 80%, antibodies against VGKC-complexes can be detected. For symptomatic treatment, anticonvulsants like carbamazepine or pregabaline are recommended. Immunoglobulins and plasmapheresis are reported as successful treatments, sometimes immunosuppressive therapy is needed.

Methods: We reviewed all patients over the past five years (2008 – 2013) of our outpatient-clinic with cramps and fasciculations. Patients with evidence for neuropathy, myopathy or motoneuron disease, even afterwards, were excluded. Nerve conduction studies and electromyography including videorecording were performed in all patients. Furthermore, immunology -esp. VGKC-antibody-complex with differentiation to CASPR2 and IGL1, cerebral fluid examinations and screening for neoplasias were done, respectively.

Results: Neuromyotonia still remains a rare disease. In our data-analysis, 37 patients fulfilled the diagnosis “benign cramp-fasciculation syndrome” (BFS) without signs of neuropathy, myopathy or motorneuron disease. In three patients, typical electromyographic changes for Neuromyotonia were found, showing spontaneous, continuous and irregular doublet, triplet or multiplet single motor unit discharges with a high intraburst frequency. Two of them had seropositive antibodies against VGKC-complex (one high and one low-titer VGKC-complex-antibodies) with very different clinical presentation. Anticonvulsants like carbamazepine (CBZ) for symptomatic treatment were moderately effective in three patients, and treatment with immunoglobulins in two patients was successful in both. Interestingly, the patient with a high titer of VGKC-complex-antibodies showed a better response to immunoglobulins than the patient with low titer-VGKC-antibody-complex. In both, VGKC-Antibody-titers did not change significantly within and after treatment with immunoglobulins.